-@c Copyright (C) 1988,1989,1992,1993,1994,1996,1998,1999,2000,2001,2002,2003,2004
-@c Free Software Foundation, Inc.
+@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1996, 1998, 1999, 2000,
+@c 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
+
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.
* Conditionals:: Omitting the middle operand of a @samp{?:} expression.
* Long Long:: Double-word integers---@code{long long int}.
* Complex:: Data types for complex numbers.
+* Decimal Float:: Decimal Floating Point.
* Hex Floats:: Hexadecimal floating-point constants.
* Zero Length:: Zero-length arrays.
* Variable Length:: Arrays whose length is computed at run time.
* Return Address:: Getting the return or frame address of a function.
* Vector Extensions:: Using vector instructions through built-in functions.
* Offsetof:: Special syntax for implementing @code{offsetof}.
+* Atomic Builtins:: Built-in functions for atomic memory access.
+* Object Size Checking:: Built-in functions for limited buffer overflow
+ checking.
* Other Builtins:: Other built-in functions.
* Target Builtins:: Built-in functions specific to particular targets.
* Target Format Checks:: Format checks specific to particular targets.
In G++, the result value of a statement expression undergoes array and
function pointer decay, and is returned by value to the enclosing
-expression. For instance, if @code{A} is a class, then
+expression. For instance, if @code{A} is a class, then
@smallexample
A a;
header files using statement-expression that lead to precisely this
bug.)
+Jumping into a statement expression with @code{goto} or using a
+@code{switch} statement outside the statement expression with a
+@code{case} or @code{default} label inside the statement expression is
+not permitted. Jumping into a statement expression with a computed
+@code{goto} (@pxref{Labels as Values}) yields undefined behavior.
+Jumping out of a statement expression is permitted, but if the
+statement expression is part of a larger expression then it is
+unspecified which other subexpressions of that expression have been
+evaluated except where the language definition requires certain
+subexpressions to be evaluated before or after the statement
+expression. In any case, as with a function call the evaluation of a
+statement expression is not interleaved with the evaluation of other
+parts of the containing expression. For example,
+
+@smallexample
+ foo (), ((@{ bar1 (); goto a; 0; @}) + bar2 ()), baz();
+@end smallexample
+
+@noindent
+will call @code{foo} and @code{bar1} and will not call @code{baz} but
+may or may not call @code{bar2}. If @code{bar2} is called, it will be
+called after @code{foo} and before @code{bar1}
+
@node Local Labels
@section Locally Declared Labels
@cindex local labels
@cindex macros, local labels
GCC allows you to declare @dfn{local labels} in any nested block
-scope. A local label is just like an ordinary label, but you can
+scope. A local label is just like an ordinary label, but you can
only reference it (with a @code{goto} statement, or by taking its
address) within the block in which it was declared.
@end smallexample
Nested function definitions are permitted within functions in the places
-where variable definitions are allowed; that is, in any block, before
-the first statement in the block.
+where variable definitions are allowed; that is, in any block, mixed
+with the other declarations and statements in the block.
It is possible to call the nested function from outside the scope of its
name by storing its address or passing the address to another function:
@end group
@end smallexample
-A nested function always has internal linkage. Declaring one with
-@code{extern} is erroneous. If you need to declare the nested function
+A nested function always has no linkage. Declaring one with
+@code{extern} or @code{static} is erroneous. If you need to declare the nested function
before its definition, use @code{auto} (which is otherwise meaningless
for function declarations).
variables are named @code{foo$real} and @code{foo$imag}. You can
examine and set these two fictitious variables with your debugger.
+@node Decimal Float
+@section Decimal Floating Point
+@cindex decimal floating point
+@cindex @code{_Decimal32} data type
+@cindex @code{_Decimal64} data type
+@cindex @code{_Decimal128} data type
+@cindex @code{df} integer suffix
+@cindex @code{dd} integer suffix
+@cindex @code{dl} integer suffix
+@cindex @code{DF} integer suffix
+@cindex @code{DD} integer suffix
+@cindex @code{DL} integer suffix
+
+GNU C supports decimal floating point types in addition to the
+standard floating-point types. This extension supports decimal
+floating-point arithmetic as defined in IEEE-754R, the proposed
+revision of IEEE-754. The C language extension is defined in ISO/IEC
+DTR 24732, Draft 5. Support for this functionality will change when
+it is accepted into the C standard and might change for new drafts
+of the proposal. Calling conventions for any target might also change.
+Not all targets support decimal floating point.
+
+Support for decimal floating point includes the arithmetic operators
+add, subtract, multiply, divide; unary arithmetic operators;
+relational operators; equality operators; and conversions to and from
+integer and other floating-point types. Use a suffix @samp{df} or
+@samp{DF} in a literal constant of type @code{_Decimal32}, @samp{dd}
+or @samp{DD} for @code{_Decimal64}, and @samp{dl} or @samp{DL} for
+@code{_Decimal128}.
+
+Passing a decimal floating-point value as an argument to a function
+without a prototype is undefined.
+
+Types @code{_Decimal32}, @code{_Decimal64}, and @code{_Decimal128}
+are supported by the DWARF2 debug information format.
+
@node Hex Floats
@section Hex Floats
@cindex hex floats
@cindex function attributes
@cindex declaring attributes of functions
@cindex functions that never return
+@cindex functions that return more than once
@cindex functions that have no side effects
@cindex functions in arbitrary sections
@cindex functions that behave like malloc
attributes when making a declaration. This keyword is followed by an
attribute specification inside double parentheses. The following
attributes are currently defined for functions on all targets:
-@code{noreturn}, @code{noinline}, @code{always_inline},
-@code{pure}, @code{const}, @code{nothrow}, @code{sentinel},
+@code{noreturn}, @code{returns_twice}, @code{noinline}, @code{always_inline},
+@code{flatten}, @code{pure}, @code{const}, @code{nothrow}, @code{sentinel},
@code{format}, @code{format_arg}, @code{no_instrument_function},
@code{section}, @code{constructor}, @code{destructor}, @code{used},
@code{unused}, @code{deprecated}, @code{weak}, @code{malloc},
-@code{alias}, @code{warn_unused_result} and @code{nonnull}. Several other
+@code{alias}, @code{warn_unused_result}, @code{nonnull}
+and @code{externally_visible}. Several other
attributes are defined for functions on particular target systems. Other
attributes, including @code{section} are supported for variables declarations
(@pxref{Variable Attributes}) and for types (@pxref{Type Attributes}).
attributes.
@table @code
-@c Keep this table alphabetized by attribute name. Treat _ as space.
+@c Keep this table alphabetized by attribute name. Treat _ as space.
@item alias ("@var{target}")
@cindex @code{alias} attribute
void f () __attribute__ ((weak, alias ("__f")));
@end smallexample
-declares @samp{f} to be a weak alias for @samp{__f}. In C++, the
-mangled name for the target must be used.
+defines @samp{f} to be a weak alias for @samp{__f}. In C++, the
+mangled name for the target must be used. It is an error if @samp{__f}
+is not defined in the same translation unit.
Not all target machines support this attribute.
For functions declared inline, this attribute inlines the function even
if no optimization level was specified.
+@cindex @code{flatten} function attribute
+@item flatten
+Generally, inlining into a function is limited. For a function marked with
+this attribute, every call inside this function will be inlined, if possible.
+Whether the function itself is considered for inlining depends on its size and
+the current inlining parameters. The @code{flatten} attribute only works
+reliably in unit-at-a-time mode.
+
@item cdecl
@cindex functions that do pop the argument stack on the 386
@opindex mrtd
@cindex @code{const} function attribute
Many functions do not examine any values except their arguments, and
have no effects except the return value. Basically this is just slightly
-more strict class than the @code{pure} attribute above, since function is not
+more strict class than the @code{pure} attribute below, since function is not
allowed to read global memory.
@cindex pointer arguments
functions, unless the @option{-fkeep-inline-functions} flag has been
used. The attribute is also ignored for undefined symbols.
-When applied to C++ classes. the attribute marks defined non-inlined
-member functions and static data members as exports. Static consts
+When applied to C++ classes, the attribute marks defined non-inlined
+member functions and static data members as exports. Static consts
initialized in-class are not marked unless they are also defined
out-of-class.
On Microsoft Windows and Symbian OS targets, the @code{dllimport}
attribute causes the compiler to reference a function or variable via
a global pointer to a pointer that is set up by the DLL exporting the
-symbol. The attribute implies @code{extern} storage. On Microsoft
+symbol. The attribute implies @code{extern} storage. On Microsoft
Windows targets, the pointer name is formed by combining @code{_imp__}
and the function or variable name.
@code{__attribute__ ((dllimport))} for compatibility with other
compilers.
-Currently, the attribute is ignored for inlined functions. If the
+Currently, the attribute is ignored for inlined functions. If the
attribute is applied to a symbol @emph{definition}, an error is reported.
If a symbol previously declared @code{dllimport} is later defined, the
attribute is ignored in subsequent references, and a warning is emitted.
using thunks.
On the SH Symbian OS target the @code{dllimport} attribute also has
-another affect - it can cause the vtable and run-time type information
+another affect---it can cause the vtable and run-time type information
for a class to be exported. This happens when the class has a
dllimport'ed constructor or a non-inline, non-pure virtual function
and, for either of those two conditions, the class also has a inline
For Microsoft Windows based targets the use of the @code{dllimport}
attribute on functions is not necessary, but provides a small
-performance benefit by eliminating a thunk in the DLL. The use of the
+performance benefit by eliminating a thunk in the DLL@. The use of the
@code{dllimport} attribute on imported variables was required on older
versions of the GNU linker, but can now be avoided by passing the
-@option{--enable-auto-import} switch to the GNU linker. As with
+@option{--enable-auto-import} switch to the GNU linker. As with
functions, using the attribute for a variable eliminates a thunk in
-the DLL.
+the DLL@.
One drawback to using this attribute is that a pointer to a function
or variable marked as @code{dllimport} cannot be used as a constant
You must use GAS and GLD from GNU binutils version 2.7 or later for
this attribute to work correctly.
+@item exception_handler
+@cindex exception handler functions on the Blackfin processor
+Use this attribute on the Blackfin to indicate that the specified function
+is an exception handler. The compiler will generate function entry and
+exit sequences suitable for use in an exception handler when this
+attribute is present.
+
@item far
@cindex functions which handle memory bank switching
On 68HC11 and 68HC12 the @code{far} attribute causes the compiler to
On 68HC11 the compiler will generate a sequence of instructions
to invoke a board-specific routine to switch the memory bank and call the
-real function. The board-specific routine simulates a @code{call}.
+real function. The board-specific routine simulates a @code{call}.
At the end of a function, it will jump to a board-specific routine
-instead of using @code{rts}. The board-specific return routine simulates
+instead of using @code{rts}. The board-specific return routine simulates
the @code{rtc}.
@item fastcall
@cindex functions that pop the argument stack on the 386
On the Intel 386, the @code{fastcall} attribute causes the compiler to
-pass the first two arguments in the registers ECX and EDX. Subsequent
-arguments are passed on the stack. The called function will pop the
-arguments off the stack. If the number of arguments is variable all
+pass the first argument (if of integral type) in the register ECX and
+the second argument (if of integral type) in the register EDX@. Subsequent
+and other typed arguments are passed on the stack. The called function will
+pop the arguments off the stack. If the number of arguments is variable all
arguments are pushed on the stack.
@item format (@var{archetype}, @var{string-index}, @var{first-to-check})
@item interrupt
@cindex interrupt handler functions
-Use this attribute on the ARM, AVR, C4x, M32R/D and Xstormy16 ports to indicate
-that the specified function is an interrupt handler. The compiler will
-generate function entry and exit sequences suitable for use in an
-interrupt handler when this attribute is present.
+Use this attribute on the ARM, AVR, C4x, CRX, M32C, M32R/D, MS1, and Xstormy16
+ports to indicate that the specified function is an interrupt handler.
+The compiler will generate function entry and exit sequences suitable
+for use in an interrupt handler when this attribute is present.
-Note, interrupt handlers for the m68k, H8/300, H8/300H, H8S, and SH processors
-can be specified via the @code{interrupt_handler} attribute.
+Note, interrupt handlers for the Blackfin, m68k, H8/300, H8/300H, H8S, and
+SH processors can be specified via the @code{interrupt_handler} attribute.
Note, on the AVR, interrupts will be enabled inside the function.
Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT and UNDEF@.
@item interrupt_handler
-@cindex interrupt handler functions on the m68k, H8/300 and SH processors
-Use this attribute on the m68k, H8/300, H8/300H, H8S, and SH to indicate that
-the specified function is an interrupt handler. The compiler will generate
-function entry and exit sequences suitable for use in an interrupt
-handler when this attribute is present.
+@cindex interrupt handler functions on the Blackfin, m68k, H8/300 and SH processors
+Use this attribute on the Blackfin, m68k, H8/300, H8/300H, H8S, and SH to
+indicate that the specified function is an interrupt handler. The compiler
+will generate function entry and exit sequences suitable for use in an
+interrupt handler when this attribute is present.
+
+@item kspisusp
+@cindex User stack pointer in interrupts on the Blackfin
+When used together with @code{interrupt_handler}, @code{exception_handler}
+or @code{nmi_handler}, code will be generated to load the stack pointer
+from the USP register in the function prologue.
@item long_call/short_call
@cindex indirect calls on ARM
This attribute specifies how a particular function is called on
ARM@. Both attributes override the @option{-mlong-calls} (@pxref{ARM Options})
command line switch and @code{#pragma long_calls} settings. The
-@code{long_call} attribute causes the compiler to always call the
-function by first loading its address into a register and then using the
-contents of that register. The @code{short_call} attribute always places
+@code{long_call} attribute indicates that the function might be far
+away from the call site and require a different (more expensive)
+calling sequence. The @code{short_call} attribute always places
the offset to the function from the call site into the @samp{BL}
instruction directly.
@item longcall/shortcall
@cindex functions called via pointer on the RS/6000 and PowerPC
-On the RS/6000 and PowerPC, the @code{longcall} attribute causes the
-compiler to always call this function via a pointer, just as it would if
-the @option{-mlongcall} option had been specified. The @code{shortcall}
-attribute causes the compiler not to do this. These attributes override
-both the @option{-mlongcall} switch and the @code{#pragma longcall}
-setting.
+On the Blackfin, RS/6000 and PowerPC, the @code{longcall} attribute
+indicates that the function might be far away from the call site and
+require a different (more expensive) calling sequence. The
+@code{shortcall} attribute indicates that the function is always close
+enough for the shorter calling sequence to be used. These attributes
+override both the @option{-mlongcall} switch and, on the RS/6000 and
+PowerPC, the @code{#pragma longcall} setting.
@xref{RS/6000 and PowerPC Options}, for more information on whether long
calls are necessary.
+@item long_call
+@cindex indirect calls on MIPS
+This attribute specifies how a particular function is called on MIPS@.
+The attribute overrides the @option{-mlong-calls} (@pxref{MIPS Options})
+command line switch. This attribute causes the compiler to always call
+the function by first loading its address into a register, and then using
+the contents of that register.
+
@item malloc
@cindex @code{malloc} attribute
The @code{malloc} attribute is used to tell the compiler that a function
This attribute can be used to cancel the effect of the @option{-mlong-calls}
option.
+@item nesting
+@cindex Allow nesting in an interrupt handler on the Blackfin processor.
+Use this attribute together with @code{interrupt_handler},
+@code{exception_handler} or @code{nmi_handler} to indicate that the function
+entry code should enable nested interrupts or exceptions.
+
+@item nmi_handler
+@cindex NMI handler functions on the Blackfin processor
+Use this attribute on the Blackfin to indicate that the specified function
+is an NMI handler. The compiler will generate function entry and
+exit sequences suitable for use in an NMI handler when this
+attribute is present.
+
@item no_instrument_function
@cindex @code{no_instrument_function} function attribute
@opindex finstrument-functions
volatile voidfn fatal;
@end smallexample
+This approach does not work in GNU C++.
+
@item nothrow
@cindex @code{nothrow} function attribute
The @code{nothrow} attribute is used to inform the compiler that a
@cindex @code{regparm} attribute
@cindex functions that are passed arguments in registers on the 386
On the Intel 386, the @code{regparm} attribute causes the compiler to
-pass up to @var{number} integer arguments in registers EAX,
-EDX, and ECX instead of on the stack. Functions that take a
-variable number of arguments will continue to be passed all of their
+pass arguments number one to @var{number} if they are of integral type
+in registers EAX, EDX, and ECX instead of on the stack. Functions that
+take a variable number of arguments will continue to be passed all of their
arguments on the stack.
Beware that on some ELF systems this attribute is unsuitable for
disabled with the linker or the loader if desired, to avoid the
problem.)
+@item sseregparm
+@cindex @code{sseregparm} attribute
+On the Intel 386 with SSE support, the @code{sseregparm} attribute
+causes the compiler to pass up to 8 floating point arguments in
+SSE registers instead of on the stack. Functions that take a
+variable number of arguments will continue to pass all of their
+floating point arguments on the stack.
+
+@item force_align_arg_pointer
+@cindex @code{force_align_arg_pointer} attribute
+On the Intel x86, the @code{force_align_arg_pointer} attribute may be
+applied to individual function definitions, generating an alternate
+prologue and epilogue that realigns the runtime stack. This supports
+mixing legacy codes that run with a 4-byte aligned stack with modern
+codes that keep a 16-byte stack for SSE compatibility. The alternate
+prologue and epilogue are slower and bigger than the regular ones, and
+the alternate prologue requires a scratch register; this lowers the
+number of registers available if used in conjunction with the
+@code{regparm} attribute. The @code{force_align_arg_pointer}
+attribute is incompatible with nested functions; this is considered a
+hard error.
+
+@item returns_twice
+@cindex @code{returns_twice} attribute
+The @code{returns_twice} attribute tells the compiler that a function may
+return more than one time. The compiler will ensure that all registers
+are dead before calling such a function and will emit a warning about
+the variables that may be clobbered after the second return from the
+function. Examples of such functions are @code{setjmp} and @code{vfork}.
+The @code{longjmp}-like counterpart of such function, if any, might need
+to be marked with the @code{noreturn} attribute.
+
@item saveall
-@cindex save all registers on the H8/300, H8/300H, and H8S
-Use this attribute on the H8/300, H8/300H, and H8S to indicate that
+@cindex save all registers on the Blackfin, H8/300, H8/300H, and H8S
+Use this attribute on the Blackfin, H8/300, H8/300H, and H8S to indicate that
all registers except the stack pointer should be saved in the prologue
regardless of whether they are used or not.
@item visibility ("@var{visibility_type}")
@cindex @code{visibility} attribute
-The @code{visibility} attribute on ELF targets causes the declaration
-to be emitted with default, hidden, protected or internal visibility.
+This attribute affects the linkage of the declaration to which it is attached.
+There are four supported @var{visibility_type} values: default,
+hidden, protected or internal visibility.
@smallexample
void __attribute__ ((visibility ("protected")))
int i __attribute__ ((visibility ("hidden")));
@end smallexample
-See the ELF gABI for complete details, but the short story is:
+The possible values of @var{visibility_type} correspond to the
+visibility settings in the ELF gABI.
@table @dfn
@c keep this list of visibilities in alphabetical order.
@item default
-Default visibility is the normal case for ELF. This value is
-available for the visibility attribute to override other options
-that may change the assumed visibility of symbols.
+Default visibility is the normal case for the object file format.
+This value is available for the visibility attribute to override other
+options that may change the assumed visibility of entities.
+
+On ELF, default visibility means that the declaration is visible to other
+modules and, in shared libraries, means that the declared entity may be
+overridden.
+
+On Darwin, default visibility means that the declaration is visible to
+other modules.
+
+Default visibility corresponds to ``external linkage'' in the language.
@item hidden
-Hidden visibility indicates that the symbol will not be placed into
-the dynamic symbol table, so no other @dfn{module} (executable or
-shared library) can reference it directly.
+Hidden visibility indicates that the entity declared will have a new
+form of linkage, which we'll call ``hidden linkage''. Two
+declarations of an object with hidden linkage refer to the same object
+if they are in the same shared object.
@item internal
Internal visibility is like hidden visibility, but with additional
-processor specific semantics. Unless otherwise specified by the psABI,
-GCC defines internal visibility to mean that the function is @emph{never}
-called from another module. Note that hidden symbols, while they cannot
-be referenced directly by other modules, can be referenced indirectly via
-function pointers. By indicating that a symbol cannot be called from
-outside the module, GCC may for instance omit the load of a PIC register
-since it is known that the calling function loaded the correct value.
+processor specific semantics. Unless otherwise specified by the
+psABI, GCC defines internal visibility to mean that a function is
+@emph{never} called from another module. Compare this with hidden
+functions which, while they cannot be referenced directly by other
+modules, can be referenced indirectly via function pointers. By
+indicating that a function cannot be called from outside the module,
+GCC may for instance omit the load of a PIC register since it is known
+that the calling function loaded the correct value.
@item protected
-Protected visibility indicates that the symbol will be placed in the
-dynamic symbol table, but that references within the defining module
-will bind to the local symbol. That is, the symbol cannot be overridden
-by another module.
+Protected visibility is like default visibility except that it
+indicates that references within the defining module will bind to the
+definition in that module. That is, the declared entity cannot be
+overridden by another module.
@end table
-Not all ELF targets support this attribute.
+All visibilities are supported on many, but not all, ELF targets
+(supported when the assembler supports the @samp{.visibility}
+pseudo-op). Default visibility is supported everywhere. Hidden
+visibility is supported on Darwin targets.
+
+The visibility attribute should be applied only to declarations which
+would otherwise have external linkage. The attribute should be applied
+consistently, so that the same entity should not be declared with
+different settings of the attribute.
+
+In C++, the visibility attribute applies to types as well as functions
+and objects, because in C++ types have linkage. A class must not have
+greater visibility than its non-static data member types and bases,
+and class members default to the visibility of their class. Also, a
+declaration without explicit visibility is limited to the visibility
+of its type.
+
+In C++, you can mark member functions and static member variables of a
+class with the visibility attribute. This is useful if if you know a
+particular method or static member variable should only be used from
+one shared object; then you can mark it hidden while the rest of the
+class has default visibility. Care must be taken to avoid breaking
+the One Definition Rule; for example, it is usually not useful to mark
+an inline method as hidden without marking the whole class as hidden.
+
+A C++ namespace declaration can also have the visibility attribute.
+This attribute applies only to the particular namespace body, not to
+other definitions of the same namespace; it is equivalent to using
+@samp{#pragma GCC visibility} before and after the namespace
+definition (@pxref{Visibility Pragmas}).
+
+In C++, if a template argument has limited visibility, this
+restriction is implicitly propagated to the template instantiation.
+Otherwise, template instantiations and specializations default to the
+visibility of their template.
+
+If both the template and enclosing class have explicit visibility, the
+visibility from the template is used.
@item warn_unused_result
@cindex @code{warn_unused_result} attribute
for ELF targets, and also for a.out targets when using the GNU assembler
and linker.
+@item weakref
+@itemx weakref ("@var{target}")
+@cindex @code{weakref} attribute
+The @code{weakref} attribute marks a declaration as a weak reference.
+Without arguments, it should be accompanied by an @code{alias} attribute
+naming the target symbol. Optionally, the @var{target} may be given as
+an argument to @code{weakref} itself. In either case, @code{weakref}
+implicitly marks the declaration as @code{weak}. Without a
+@var{target}, given as an argument to @code{weakref} or to @code{alias},
+@code{weakref} is equivalent to @code{weak}.
+
+@smallexample
+static int x() __attribute__ ((weakref ("y")));
+/* is equivalent to... */
+static int x() __attribute__ ((weak, weakref, alias ("y")));
+/* and to... */
+static int x() __attribute__ ((weakref));
+static int x() __attribute__ ((alias ("y")));
+@end smallexample
+
+A weak reference is an alias that does not by itself require a
+definition to be given for the target symbol. If the target symbol is
+only referenced through weak references, then the becomes a @code{weak}
+undefined symbol. If it is directly referenced, however, then such
+strong references prevail, and a definition will be required for the
+symbol, not necessarily in the same translation unit.
+
+The effect is equivalent to moving all references to the alias to a
+separate translation unit, renaming the alias to the aliased symbol,
+declaring it as weak, compiling the two separate translation units and
+performing a reloadable link on them.
+
+At present, a declaration to which @code{weakref} is attached can
+only be @code{static}.
+
+@item externally_visible
+@cindex @code{externally_visible} attribute.
+This attribute, attached to a global variable or function nullify
+effect of @option{-fwhole-program} command line option, so the object
+remain visible outside the current compilation unit
+
@end table
You can specify multiple attributes in a declaration by separating them
that may be unused but which is compiled with @option{-Wall}. It would
not normally be appropriate to use in it human-written code, though it
could be useful in cases where the code that jumps to the label is
-contained within an @code{#ifdef} conditional. GNU C++ does not permit
+contained within an @code{#ifdef} conditional. GNU C++ does not permit
such placement of attribute lists, as it is permissible for a
declaration, which could begin with an attribute list, to be labelled in
-C++. Declarations cannot be labelled in C90 or C99, so the ambiguity
+C++. Declarations cannot be labelled in C90 or C99, so the ambiguity
does not arise there.
An attribute specifier list may appear as part of a @code{struct},
@code{union} or @code{enum} specifier. It may go either immediately
after the @code{struct}, @code{union} or @code{enum} keyword, or after
-the closing brace. It is ignored if the content of the structure, union
-or enumerated type is not defined in the specifier in which the
-attribute specifier list is used---that is, in usages such as
-@code{struct __attribute__((foo)) bar} with no following opening brace.
+the closing brace. The former syntax is preferred.
Where attribute specifiers follow the closing brace, they are considered
to relate to the structure, union or enumerated type defined, not to any
enclosing declaration the type specifier appears in, and the type
/* @r{Old-style function definition.} */
int
-isroot (x) /* ??? lossage here ??? */
+isroot (x) /* @r{??? lossage here ???} */
uid_t x;
@{
return x == 0;
@opindex fno-common
The @code{common} attribute requests GCC to place a variable in
``common'' storage. The @code{nocommon} attribute requests the
-opposite -- to allocate space for it directly.
+opposite---to allocate space for it directly.
These attributes override the default chosen by the
@option{-fno-common} and @option{-fcommon} flags respectively.
main()
@{
- /* Initialize stack pointer */
+ /* @r{Initialize stack pointer} */
init_sp (stack + sizeof (stack));
- /* Initialize initialized data */
+ /* @r{Initialize initialized data} */
memcpy (&init_data, &data, &edata - &data);
- /* Turn on the serial ports */
+ /* @r{Turn on the serial ports} */
init_duart (&a);
init_duart (&b);
@}
int
main()
@{
- /* Read and write foo. All running
- copies see the same value. */
+ /* @r{Read and write foo. All running
+ copies see the same value.} */
return 0;
@}
@end smallexample
Not all targets support this attribute.
-@item transparent_union
-This attribute, attached to a function parameter which is a union, means
-that the corresponding argument may have the type of any union member,
-but the argument is passed as if its type were that of the first union
-member. For more details see @xref{Type Attributes}. You can also use
-this attribute on a @code{typedef} for a union data type; then it
-applies to all function parameters with that type.
-
@item unused
This attribute, attached to a variable, means that the variable is meant
to be possibly unused. GCC will not produce a warning for this
is invalid even if the size of the structure is the same as the size of
the @code{int}.
+@item selectany
+The @code{selectany} attribute causes an initialized global variable to
+have link-once semantics. When multiple definitions of the variable are
+encountered by the linker, the first is selected and the remainder are
+discarded. Following usage by the Microsoft compiler, the linker is told
+@emph{not} to warn about size or content differences of the multiple
+definitions.
+
+Although the primary usage of this attribute is for POD types, the
+attribute can also be applied to global C++ objects that are initialized
+by a constructor. In this case, the static initialization and destruction
+code for the object is emitted in each translation defining the object,
+but the calls to the constructor and destructor are protected by a
+link-once guard variable.
+
+The @code{selectany} attribute is only available on Microsoft Windows
+targets. You can use @code{__declspec (selectany)} as a synonym for
+@code{__attribute__ ((selectany))} for compatibility with other
+compilers.
+
@item weak
The @code{weak} attribute is described in @xref{Function Attributes}.
@subsection M32R/D Variable Attributes
-One attribute is currently defined for the M32R/D.
+One attribute is currently defined for the M32R/D@.
@table @code
@item model (@var{model-name})
addresses).
@end table
+@anchor{i386 Variable Attributes}
@subsection i386 Variable Attributes
Two attributes are currently defined for i386 configurations:
Currently @option{-m[no-]ms-bitfields} is provided for the Microsoft Windows X86
compilers to match the native Microsoft compiler.
+
+The Microsoft structure layout algorithm is fairly simple with the exception
+of the bitfield packing:
+
+The padding and alignment of members of structures and whether a bit field
+can straddle a storage-unit boundary
+
+@enumerate
+@item Structure members are stored sequentially in the order in which they are
+declared: the first member has the lowest memory address and the last member
+the highest.
+
+@item Every data object has an alignment-requirement. The alignment-requirement
+for all data except structures, unions, and arrays is either the size of the
+object or the current packing size (specified with either the aligned attribute
+or the pack pragma), whichever is less. For structures, unions, and arrays,
+the alignment-requirement is the largest alignment-requirement of its members.
+Every object is allocated an offset so that:
+
+offset % alignment-requirement == 0
+
+@item Adjacent bit fields are packed into the same 1-, 2-, or 4-byte allocation
+unit if the integral types are the same size and if the next bit field fits
+into the current allocation unit without crossing the boundary imposed by the
+common alignment requirements of the bit fields.
+@end enumerate
+
+Handling of zero-length bitfields:
+
+MSVC interprets zero-length bitfields in the following ways:
+
+@enumerate
+@item If a zero-length bitfield is inserted between two bitfields that would
+normally be coalesced, the bitfields will not be coalesced.
+
+For example:
+
+@smallexample
+struct
+ @{
+ unsigned long bf_1 : 12;
+ unsigned long : 0;
+ unsigned long bf_2 : 12;
+ @} t1;
+@end smallexample
+
+The size of @code{t1} would be 8 bytes with the zero-length bitfield. If the
+zero-length bitfield were removed, @code{t1}'s size would be 4 bytes.
+
+@item If a zero-length bitfield is inserted after a bitfield, @code{foo}, and the
+alignment of the zero-length bitfield is greater than the member that follows it,
+@code{bar}, @code{bar} will be aligned as the type of the zero-length bitfield.
+
+For example:
+
+@smallexample
+struct
+ @{
+ char foo : 4;
+ short : 0;
+ char bar;
+ @} t2;
+
+struct
+ @{
+ char foo : 4;
+ short : 0;
+ double bar;
+ @} t3;
+@end smallexample
+
+For @code{t2}, @code{bar} will be placed at offset 2, rather than offset 1.
+Accordingly, the size of @code{t2} will be 4. For @code{t3}, the zero-length
+bitfield will not affect the alignment of @code{bar} or, as a result, the size
+of the structure.
+
+Taking this into account, it is important to note the following:
+
+@enumerate
+@item If a zero-length bitfield follows a normal bitfield, the type of the
+zero-length bitfield may affect the alignment of the structure as whole. For
+example, @code{t2} has a size of 4 bytes, since the zero-length bitfield follows a
+normal bitfield, and is of type short.
+
+@item Even if a zero-length bitfield is not followed by a normal bitfield, it may
+still affect the alignment of the structure:
+
+@smallexample
+struct
+ @{
+ char foo : 6;
+ long : 0;
+ @} t4;
+@end smallexample
+
+Here, @code{t4} will take up 4 bytes.
+@end enumerate
+
+@item Zero-length bitfields following non-bitfield members are ignored:
+
+@smallexample
+struct
+ @{
+ char foo;
+ long : 0;
+ char bar;
+ @} t5;
+@end smallexample
+
+Here, @code{t5} will take up 2 bytes.
+@end enumerate
@end table
+@subsection PowerPC Variable Attributes
+
+Three attributes currently are defined for PowerPC configurations:
+@code{altivec}, @code{ms_struct} and @code{gcc_struct}.
+
+For full documentation of the struct attributes please see the
+documentation in the @xref{i386 Variable Attributes}, section.
+
+For documentation of @code{altivec} attribute please see the
+documentation in the @xref{PowerPC Type Attributes}, section.
+
@subsection Xstormy16 Variable Attributes
One attribute is currently defined for xstormy16 configurations:
@cindex type attributes
The keyword @code{__attribute__} allows you to specify special
-attributes of @code{struct} and @code{union} types when you define such
-types. This keyword is followed by an attribute specification inside
-double parentheses. Six attributes are currently defined for types:
-@code{aligned}, @code{packed}, @code{transparent_union}, @code{unused},
-@code{deprecated} and @code{may_alias}. Other attributes are defined for
-functions (@pxref{Function Attributes}) and for variables
-(@pxref{Variable Attributes}).
+attributes of @code{struct} and @code{union} types when you define
+such types. This keyword is followed by an attribute specification
+inside double parentheses. Seven attributes are currently defined for
+types: @code{aligned}, @code{packed}, @code{transparent_union},
+@code{unused}, @code{deprecated}, @code{visibility}, and
+@code{may_alias}. Other attributes are defined for functions
+(@pxref{Function Attributes}) and for variables (@pxref{Variable
+Attributes}).
You may also specify any one of these attributes with @samp{__}
preceding and following its keyword. This allows you to use these
macro of the same name. For example, you may use @code{__aligned__}
instead of @code{aligned}.
-You may specify the @code{aligned} and @code{transparent_union}
-attributes either in a @code{typedef} declaration or just past the
-closing curly brace of a complete enum, struct or union type
-@emph{definition} and the @code{packed} attribute only past the closing
-brace of a definition.
+You may specify type attributes either in a @code{typedef} declaration
+or in an enum, struct or union type declaration or definition.
-You may also specify attributes between the enum, struct or union
-tag and the name of the type rather than after the closing brace.
+For an enum, struct or union type, you may specify attributes either
+between the enum, struct or union tag and the name of the type, or
+just past the closing curly brace of the @emph{definition}. The
+former syntax is preferred.
@xref{Attribute Syntax}, for details of the exact syntax for using
attributes.
@item packed
This attribute, attached to @code{struct} or @code{union} type
-definition, specifies that each member of the structure or union is
-placed to minimize the memory required. When attached to an @code{enum}
-definition, it indicates that the smallest integral type should be used.
+definition, specifies that each member (other than zero-width bitfields)
+of the structure or union is placed to minimize the memory required. When
+attached to an @code{enum} definition, it indicates that the smallest
+integral type should be used.
@opindex fshort-enums
Specifying this attribute for @code{struct} and @code{union} types is
In the following example @code{struct my_packed_struct}'s members are
packed closely together, but the internal layout of its @code{s} member
-is not packed -- to do that, @code{struct my_unpacked_struct} would need to
+is not packed---to do that, @code{struct my_unpacked_struct} would need to
be packed too.
@smallexample
int i;
@};
-struct my_packed_struct __attribute__ ((__packed__))
+struct __attribute__ ((__packed__)) my_packed_struct
@{
char c;
int i;
@option{-fstrict-aliasing}, which is on by default at @option{-O2} or
above in recent GCC versions.
+@item visibility
+In C++, attribute visibility (@pxref{Function Attributes}) can also be
+applied to class, struct, union and enum types. Unlike other type
+attributes, the attribute must appear between the initial keyword and
+the name of the type; it cannot appear after the body of the type.
+
+Note that the type visibility is applied to vague linkage entities
+associated with the class (vtable, typeinfo node, etc.). In
+particular, if a class is thrown as an exception in one shared object
+and caught in another, the class must have default visibility.
+Otherwise the two shared objects will be unable to use the same
+typeinfo node and exception handling will break.
+
+@subsection ARM Type Attributes
+
+On those ARM targets that support @code{dllimport} (such as Symbian
+OS), you can use the @code{notshared} attribute to indicate that the
+virtual table and other similar data for a class should not be
+exported from a DLL@. For example:
+
+@smallexample
+class __declspec(notshared) C @{
+public:
+ __declspec(dllimport) C();
+ virtual void f();
+@}
+
+__declspec(dllexport)
+C::C() @{@}
+@end smallexample
+
+In this code, @code{C::C} is exported from the current DLL, but the
+virtual table for @code{C} is not exported. (You can use
+@code{__attribute__} instead of @code{__declspec} if you prefer, but
+most Symbian OS code uses @code{__declspec}.)
+
+@anchor{i386 Type Attributes}
@subsection i386 Type Attributes
Two attributes are currently defined for i386 configurations:
double parentheses: for example, @samp{__attribute__ ((aligned (16),
packed))}.
+@anchor{PowerPC Type Attributes}
+@subsection PowerPC Type Attributes
+
+Three attributes currently are defined for PowerPC configurations:
+@code{altivec}, @code{ms_struct} and @code{gcc_struct}.
+
+For full documentation of the struct attributes please see the
+documentation in the @xref{i386 Type Attributes}, section.
+
+The @code{altivec} attribute allows one to declare AltiVec vector data
+types supported by the AltiVec Programming Interface Manual. The
+attribute requires an argument to specify one of three vector types:
+@code{vector__}, @code{pixel__} (always followed by unsigned short),
+and @code{bool__} (always followed by unsigned).
+
+@smallexample
+__attribute__((altivec(vector__)))
+__attribute__((altivec(pixel__))) unsigned short
+__attribute__((altivec(bool__))) unsigned
+@end smallexample
+
+These attributes mainly are intended to support the @code{__vector},
+@code{__pixel}, and @code{__bool} AltiVec keywords.
+
@node Inline
@section An Inline Function is As Fast As a Macro
@cindex inline functions
the @samp{always_inline} attribute for the function, like this:
@smallexample
-/* Prototype. */
+/* @r{Prototype.} */
inline void foo (const char) __attribute__((always_inline));
@end smallexample
output operand from the first input, if any. Commas separate the
operands within each group. The total number of operands is currently
limited to 30; this limitation may be lifted in some future version of
-GCC.
+GCC@.
If there are no output operands but there are input operands, you must
place two consecutive colons surrounding the place where the output
@smallexample
asm volatile ("movc3 %0,%1,%2"
- : /* no outputs */
+ : /* @r{no outputs} */
: "g" (from), "g" (to), "g" (count)
: "r0", "r1", "r2", "r3", "r4", "r5");
@end smallexample
int result;
asm ("magic stuff accessing an 'int' pointed to by '%1'"
"=&d" (r) : "a" (y), "m" (*y));
- return result;
+ return result;
@}
@end smallexample
important side-effects. GCC will not delete a volatile @code{asm} if
it is reachable. (The instruction can still be deleted if GCC can
prove that control-flow will never reach the location of the
-instruction.) Note that even a volatile @code{asm} instruction
+instruction.) Note that even a volatile @code{asm} instruction
can be moved relative to other code, including across jump
-instructions. For example, on many targets there is a system
-register which can be set to control the rounding mode of
+instructions. For example, on many targets there is a system
+register which can be set to control the rounding mode of
floating point operations. You might try
setting it with a volatile @code{asm}, like this PowerPC example:
one of its callers. The @var{level} argument is number of frames to
scan up the call stack. A value of @code{0} yields the return address
of the current function, a value of @code{1} yields the return address
-of the caller of the current function, and so forth. When inlining
+of the caller of the current function, and so forth. When inlining
the expected behavior is that the function will return the address of
the function that will be returned to. To work around this behavior use
the @code{noinline} function attribute.
On some machines it may be impossible to determine the return address of
any function other than the current one; in such cases, or when the top
of the stack has been reached, this function will return @code{0} or a
-random value. In addition, @code{__builtin_frame_address} may be used
+random value. In addition, @code{__builtin_frame_address} may be used
to determine if the top of the stack has been reached.
This function should only be used with a nonzero argument for debugging
may be dependent. In either case, @var{member} may consist of a single
identifier, or a sequence of member accesses and array references.
+@node Atomic Builtins
+@section Built-in functions for atomic memory access
+
+The following builtins are intended to be compatible with those described
+in the @cite{Intel Itanium Processor-specific Application Binary Interface},
+section 7.4. As such, they depart from the normal GCC practice of using
+the ``__builtin_'' prefix, and further that they are overloaded such that
+they work on multiple types.
+
+The definition given in the Intel documentation allows only for the use of
+the types @code{int}, @code{long}, @code{long long} as well as their unsigned
+counterparts. GCC will allow any integral scalar or pointer type that is
+1, 2, 4 or 8 bytes in length.
+
+Not all operations are supported by all target processors. If a particular
+operation cannot be implemented on the target processor, a warning will be
+generated and a call an external function will be generated. The external
+function will carry the same name as the builtin, with an additional suffix
+@samp{_@var{n}} where @var{n} is the size of the data type.
+
+@c ??? Should we have a mechanism to suppress this warning? This is almost
+@c useful for implementing the operation under the control of an external
+@c mutex.
+
+In most cases, these builtins are considered a @dfn{full barrier}. That is,
+no memory operand will be moved across the operation, either forward or
+backward. Further, instructions will be issued as necessary to prevent the
+processor from speculating loads across the operation and from queuing stores
+after the operation.
+
+All of the routines are are described in the Intel documentation to take
+``an optional list of variables protected by the memory barrier''. It's
+not clear what is meant by that; it could mean that @emph{only} the
+following variables are protected, or it could mean that these variables
+should in addition be protected. At present GCC ignores this list and
+protects all variables which are globally accessible. If in the future
+we make some use of this list, an empty list will continue to mean all
+globally accessible variables.
+
+@table @code
+@item @var{type} __sync_fetch_and_add (@var{type} *ptr, @var{type} value, ...)
+@itemx @var{type} __sync_fetch_and_sub (@var{type} *ptr, @var{type} value, ...)
+@itemx @var{type} __sync_fetch_and_or (@var{type} *ptr, @var{type} value, ...)
+@itemx @var{type} __sync_fetch_and_and (@var{type} *ptr, @var{type} value, ...)
+@itemx @var{type} __sync_fetch_and_xor (@var{type} *ptr, @var{type} value, ...)
+@itemx @var{type} __sync_fetch_and_nand (@var{type} *ptr, @var{type} value, ...)
+@findex __sync_fetch_and_add
+@findex __sync_fetch_and_sub
+@findex __sync_fetch_and_or
+@findex __sync_fetch_and_and
+@findex __sync_fetch_and_xor
+@findex __sync_fetch_and_nand
+These builtins perform the operation suggested by the name, and
+returns the value that had previously been in memory. That is,
+
+@smallexample
+@{ tmp = *ptr; *ptr @var{op}= value; return tmp; @}
+@{ tmp = *ptr; *ptr = ~tmp & value; return tmp; @} // nand
+@end smallexample
+
+@item @var{type} __sync_add_and_fetch (@var{type} *ptr, @var{type} value, ...)
+@itemx @var{type} __sync_sub_and_fetch (@var{type} *ptr, @var{type} value, ...)
+@itemx @var{type} __sync_or_and_fetch (@var{type} *ptr, @var{type} value, ...)
+@itemx @var{type} __sync_and_and_fetch (@var{type} *ptr, @var{type} value, ...)
+@itemx @var{type} __sync_xor_and_fetch (@var{type} *ptr, @var{type} value, ...)
+@itemx @var{type} __sync_nand_and_fetch (@var{type} *ptr, @var{type} value, ...)
+@findex __sync_add_and_fetch
+@findex __sync_sub_and_fetch
+@findex __sync_or_and_fetch
+@findex __sync_and_and_fetch
+@findex __sync_xor_and_fetch
+@findex __sync_nand_and_fetch
+These builtins perform the operation suggested by the name, and
+return the new value. That is,
+
+@smallexample
+@{ *ptr @var{op}= value; return *ptr; @}
+@{ *ptr = ~*ptr & value; return *ptr; @} // nand
+@end smallexample
+
+@item bool __sync_bool_compare_and_swap (@var{type} *ptr, @var{type} oldval @var{type} newval, ...)
+@itemx @var{type} __sync_val_compare_and_swap (@var{type} *ptr, @var{type} oldval @var{type} newval, ...)
+@findex __sync_bool_compare_and_swap
+@findex __sync_val_compare_and_swap
+These builtins perform an atomic compare and swap. That is, if the current
+value of @code{*@var{ptr}} is @var{oldval}, then write @var{newval} into
+@code{*@var{ptr}}.
+
+The ``bool'' version returns true if the comparison is successful and
+@var{newval} was written. The ``val'' version returns the contents
+of @code{*@var{ptr}} before the operation.
+
+@item __sync_synchronize (...)
+@findex __sync_synchronize
+This builtin issues a full memory barrier.
+
+@item @var{type} __sync_lock_test_and_set (@var{type} *ptr, @var{type} value, ...)
+@findex __sync_lock_test_and_set
+This builtin, as described by Intel, is not a traditional test-and-set
+operation, but rather an atomic exchange operation. It writes @var{value}
+into @code{*@var{ptr}}, and returns the previous contents of
+@code{*@var{ptr}}.
+
+Many targets have only minimal support for such locks, and do not support
+a full exchange operation. In this case, a target may support reduced
+functionality here by which the @emph{only} valid value to store is the
+immediate constant 1. The exact value actually stored in @code{*@var{ptr}}
+is implementation defined.
+
+This builtin is not a full barrier, but rather an @dfn{acquire barrier}.
+This means that references after the builtin cannot move to (or be
+speculated to) before the builtin, but previous memory stores may not
+be globally visible yet, and previous memory loads may not yet be
+satisfied.
+
+@item void __sync_lock_release (@var{type} *ptr, ...)
+@findex __sync_lock_release
+This builtin releases the lock acquired by @code{__sync_lock_test_and_set}.
+Normally this means writing the constant 0 to @code{*@var{ptr}}.
+
+This builtin is not a full barrier, but rather a @dfn{release barrier}.
+This means that all previous memory stores are globally visible, and all
+previous memory loads have been satisfied, but following memory reads
+are not prevented from being speculated to before the barrier.
+@end table
+
+@node Object Size Checking
+@section Object Size Checking Builtins
+@findex __builtin_object_size
+@findex __builtin___memcpy_chk
+@findex __builtin___mempcpy_chk
+@findex __builtin___memmove_chk
+@findex __builtin___memset_chk
+@findex __builtin___strcpy_chk
+@findex __builtin___stpcpy_chk
+@findex __builtin___strncpy_chk
+@findex __builtin___strcat_chk
+@findex __builtin___strncat_chk
+@findex __builtin___sprintf_chk
+@findex __builtin___snprintf_chk
+@findex __builtin___vsprintf_chk
+@findex __builtin___vsnprintf_chk
+@findex __builtin___printf_chk
+@findex __builtin___vprintf_chk
+@findex __builtin___fprintf_chk
+@findex __builtin___vfprintf_chk
+
+GCC implements a limited buffer overflow protection mechanism
+that can prevent some buffer overflow attacks.
+
+@deftypefn {Built-in Function} {size_t} __builtin_object_size (void * @var{ptr}, int @var{type})
+is a built-in construct that returns a constant number of bytes from
+@var{ptr} to the end of the object @var{ptr} pointer points to
+(if known at compile time). @code{__builtin_object_size} never evaluates
+its arguments for side-effects. If there are any side-effects in them, it
+returns @code{(size_t) -1} for @var{type} 0 or 1 and @code{(size_t) 0}
+for @var{type} 2 or 3. If there are multiple objects @var{ptr} can
+point to and all of them are known at compile time, the returned number
+is the maximum of remaining byte counts in those objects if @var{type} & 2 is
+0 and minimum if nonzero. If it is not possible to determine which objects
+@var{ptr} points to at compile time, @code{__builtin_object_size} should
+return @code{(size_t) -1} for @var{type} 0 or 1 and @code{(size_t) 0}
+for @var{type} 2 or 3.
+
+@var{type} is an integer constant from 0 to 3. If the least significant
+bit is clear, objects are whole variables, if it is set, a closest
+surrounding subobject is considered the object a pointer points to.
+The second bit determines if maximum or minimum of remaining bytes
+is computed.
+
+@smallexample
+struct V @{ char buf1[10]; int b; char buf2[10]; @} var;
+char *p = &var.buf1[1], *q = &var.b;
+
+/* Here the object p points to is var. */
+assert (__builtin_object_size (p, 0) == sizeof (var) - 1);
+/* The subobject p points to is var.buf1. */
+assert (__builtin_object_size (p, 1) == sizeof (var.buf1) - 1);
+/* The object q points to is var. */
+assert (__builtin_object_size (q, 0)
+ == (char *) (&var + 1) - (char *) &var.b);
+/* The subobject q points to is var.b. */
+assert (__builtin_object_size (q, 1) == sizeof (var.b));
+@end smallexample
+@end deftypefn
+
+There are built-in functions added for many common string operation
+functions, e.g. for @code{memcpy} @code{__builtin___memcpy_chk}
+built-in is provided. This built-in has an additional last argument,
+which is the number of bytes remaining in object the @var{dest}
+argument points to or @code{(size_t) -1} if the size is not known.
+
+The built-in functions are optimized into the normal string functions
+like @code{memcpy} if the last argument is @code{(size_t) -1} or if
+it is known at compile time that the destination object will not
+be overflown. If the compiler can determine at compile time the
+object will be always overflown, it issues a warning.
+
+The intended use can be e.g.
+
+@smallexample
+#undef memcpy
+#define bos0(dest) __builtin_object_size (dest, 0)
+#define memcpy(dest, src, n) \
+ __builtin___memcpy_chk (dest, src, n, bos0 (dest))
+
+char *volatile p;
+char buf[10];
+/* It is unknown what object p points to, so this is optimized
+ into plain memcpy - no checking is possible. */
+memcpy (p, "abcde", n);
+/* Destination is known and length too. It is known at compile
+ time there will be no overflow. */
+memcpy (&buf[5], "abcde", 5);
+/* Destination is known, but the length is not known at compile time.
+ This will result in __memcpy_chk call that can check for overflow
+ at runtime. */
+memcpy (&buf[5], "abcde", n);
+/* Destination is known and it is known at compile time there will
+ be overflow. There will be a warning and __memcpy_chk call that
+ will abort the program at runtime. */
+memcpy (&buf[6], "abcde", 5);
+@end smallexample
+
+Such built-in functions are provided for @code{memcpy}, @code{mempcpy},
+@code{memmove}, @code{memset}, @code{strcpy}, @code{stpcpy}, @code{strncpy},
+@code{strcat} and @code{strncat}.
+
+There are also checking built-in functions for formatted output functions.
+@smallexample
+int __builtin___sprintf_chk (char *s, int flag, size_t os, const char *fmt, ...);
+int __builtin___snprintf_chk (char *s, size_t maxlen, int flag, size_t os,
+ const char *fmt, ...);
+int __builtin___vsprintf_chk (char *s, int flag, size_t os, const char *fmt,
+ va_list ap);
+int __builtin___vsnprintf_chk (char *s, size_t maxlen, int flag, size_t os,
+ const char *fmt, va_list ap);
+@end smallexample
+
+The added @var{flag} argument is passed unchanged to @code{__sprintf_chk}
+etc. functions and can contain implementation specific flags on what
+additional security measures the checking function might take, such as
+handling @code{%n} differently.
+
+The @var{os} argument is the object size @var{s} points to, like in the
+other built-in functions. There is a small difference in the behavior
+though, if @var{os} is @code{(size_t) -1}, the built-in functions are
+optimized into the non-checking functions only if @var{flag} is 0, otherwise
+the checking function is called with @var{os} argument set to
+@code{(size_t) -1}.
+
+In addition to this, there are checking built-in functions
+@code{__builtin___printf_chk}, @code{__builtin___vprintf_chk},
+@code{__builtin___fprintf_chk} and @code{__builtin___vfprintf_chk}.
+These have just one additional argument, @var{flag}, right before
+format string @var{fmt}. If the compiler is able to optimize them to
+@code{fputc} etc. functions, it will, otherwise the checking function
+should be called and the @var{flag} argument passed to it.
+
@node Other Builtins
@section Other built-in functions provided by GCC
@cindex built-in functions
@findex __builtin_islessequal
@findex __builtin_islessgreater
@findex __builtin_isunordered
+@findex __builtin_powi
+@findex __builtin_powif
+@findex __builtin_powil
@findex _Exit
@findex _exit
@findex abort
@findex cimag
@findex cimagf
@findex cimagl
+@findex clog
+@findex clogf
+@findex clogl
@findex conj
@findex conjf
@findex conjl
@findex sqrtl
@findex sscanf
@findex stpcpy
+@findex stpncpy
+@findex strcasecmp
@findex strcat
@findex strchr
@findex strcmp
@findex strfmon
@findex strftime
@findex strlen
+@findex strncasecmp
@findex strncat
@findex strncmp
@findex strncpy
+@findex strndup
@findex strpbrk
@findex strrchr
@findex strspn
GCC includes built-in versions of many of the functions in the standard
C library. The versions prefixed with @code{__builtin_} will always be
treated as having the same meaning as the C library function even if you
-specify the @option{-fno-builtin} option. (@pxref{C Dialect Options})
+specify the @option{-fno-builtin} option. (@pxref{C Dialect Options})
Many of these functions are only optimized in certain cases; if they are
not optimized in a particular case, a call to the library function will
be emitted.
@code{scalb}, @code{signbit}, @code{signbitf}, @code{signbitl},
@code{significandf}, @code{significandl}, @code{significand},
@code{sincosf}, @code{sincosl}, @code{sincos}, @code{stpcpy},
-@code{strdup}, @code{strfmon}, @code{toascii}, @code{y0f}, @code{y0l},
-@code{y0}, @code{y1f}, @code{y1l}, @code{y1}, @code{ynf}, @code{ynl} and
-@code{yn}
+@code{stpncpy}, @code{strcasecmp}, @code{strdup}, @code{strfmon},
+@code{strncasecmp}, @code{strndup}, @code{toascii}, @code{y0f},
+@code{y0l}, @code{y0}, @code{y1f}, @code{y1l}, @code{y1}, @code{ynf},
+@code{ynl} and @code{yn}
may be handled as built-in functions.
All these functions have corresponding versions
prefixed with @code{__builtin_}, which may be used even in strict C89
@code{catanl}, @code{catan}, @code{cbrtf}, @code{cbrtl}, @code{cbrt},
@code{ccosf}, @code{ccoshf}, @code{ccoshl}, @code{ccosh}, @code{ccosl},
@code{ccos}, @code{cexpf}, @code{cexpl}, @code{cexp}, @code{cimagf},
-@code{cimagl}, @code{cimag}, @code{conjf}, @code{conjl}, @code{conj},
-@code{copysignf}, @code{copysignl}, @code{copysign}, @code{cpowf},
-@code{cpowl}, @code{cpow}, @code{cprojf}, @code{cprojl}, @code{cproj},
-@code{crealf}, @code{creall}, @code{creal}, @code{csinf}, @code{csinhf},
-@code{csinhl}, @code{csinh}, @code{csinl}, @code{csin}, @code{csqrtf},
-@code{csqrtl}, @code{csqrt}, @code{ctanf}, @code{ctanhf}, @code{ctanhl},
-@code{ctanh}, @code{ctanl}, @code{ctan}, @code{erfcf}, @code{erfcl},
-@code{erfc}, @code{erff}, @code{erfl}, @code{erf}, @code{exp2f},
-@code{exp2l}, @code{exp2}, @code{expm1f}, @code{expm1l}, @code{expm1},
-@code{fdimf}, @code{fdiml}, @code{fdim}, @code{fmaf}, @code{fmal},
-@code{fmaxf}, @code{fmaxl}, @code{fmax}, @code{fma}, @code{fminf},
-@code{fminl}, @code{fmin}, @code{hypotf}, @code{hypotl}, @code{hypot},
-@code{ilogbf}, @code{ilogbl}, @code{ilogb}, @code{imaxabs},
-@code{isblank}, @code{iswblank}, @code{lgammaf}, @code{lgammal},
-@code{lgamma}, @code{llabs}, @code{llrintf}, @code{llrintl},
+@code{cimagl}, @code{cimag}, @code{clogf}, @code{clogl}, @code{clog},
+@code{conjf}, @code{conjl}, @code{conj}, @code{copysignf}, @code{copysignl},
+@code{copysign}, @code{cpowf}, @code{cpowl}, @code{cpow}, @code{cprojf},
+@code{cprojl}, @code{cproj}, @code{crealf}, @code{creall}, @code{creal},
+@code{csinf}, @code{csinhf}, @code{csinhl}, @code{csinh}, @code{csinl},
+@code{csin}, @code{csqrtf}, @code{csqrtl}, @code{csqrt}, @code{ctanf},
+@code{ctanhf}, @code{ctanhl}, @code{ctanh}, @code{ctanl}, @code{ctan},
+@code{erfcf}, @code{erfcl}, @code{erfc}, @code{erff}, @code{erfl},
+@code{erf}, @code{exp2f}, @code{exp2l}, @code{exp2}, @code{expm1f},
+@code{expm1l}, @code{expm1}, @code{fdimf}, @code{fdiml}, @code{fdim},
+@code{fmaf}, @code{fmal}, @code{fmaxf}, @code{fmaxl}, @code{fmax},
+@code{fma}, @code{fminf}, @code{fminl}, @code{fmin}, @code{hypotf},
+@code{hypotl}, @code{hypot}, @code{ilogbf}, @code{ilogbl}, @code{ilogb},
+@code{imaxabs}, @code{isblank}, @code{iswblank}, @code{lgammaf},
+@code{lgammal}, @code{lgamma}, @code{llabs}, @code{llrintf}, @code{llrintl},
@code{llrint}, @code{llroundf}, @code{llroundl}, @code{llround},
@code{log1pf}, @code{log1pl}, @code{log1p}, @code{log2f}, @code{log2l},
@code{log2}, @code{logbf}, @code{logbl}, @code{logb}, @code{lrintf},
@})
@end smallexample
-@emph{Note:} This construct is only available for C.
+@emph{Note:} This construct is only available for C@.
@end deftypefn
(void)0))
@end smallexample
-@emph{Note:} This construct is only available for C. Furthermore, the
+@emph{Note:} This construct is only available for C@. Furthermore, the
unused expression (@var{exp1} or @var{exp2} depending on the value of
@var{const_exp}) may still generate syntax errors. This may change in
future revisions.
@deftypefn {Built-in Function} double __builtin_inf (void)
Similar to @code{__builtin_huge_val}, except a warning is generated
if the target floating-point format does not support infinities.
-This function is suitable for implementing the ISO C99 macro @code{INFINITY}.
+@end deftypefn
+
+@deftypefn {Built-in Function} _Decimal32 __builtin_infd32 (void)
+Similar to @code{__builtin_inf}, except the return type is @code{_Decimal32}.
+@end deftypefn
+
+@deftypefn {Built-in Function} _Decimal64 __builtin_infd64 (void)
+Similar to @code{__builtin_inf}, except the return type is @code{_Decimal64}.
+@end deftypefn
+
+@deftypefn {Built-in Function} _Decimal128 __builtin_infd128 (void)
+Similar to @code{__builtin_inf}, except the return type is @code{_Decimal128}.
@end deftypefn
@deftypefn {Built-in Function} float __builtin_inff (void)
Similar to @code{__builtin_inf}, except the return type is @code{float}.
+This function is suitable for implementing the ISO C99 macro @code{INFINITY}.
@end deftypefn
@deftypefn {Built-in Function} {long double} __builtin_infl (void)
in the significand such that the least significant bit of the number
is at the least significant bit of the significand. The number is
truncated to fit the significand field provided. The significand is
-forced to be a quiet NaN.
+forced to be a quiet NaN@.
+
+This function, if given a string literal all of which would have been
+consumed by strtol, is evaluated early enough that it is considered a
+compile-time constant.
+@end deftypefn
+
+@deftypefn {Built-in Function} _Decimal32 __builtin_nand32 (const char *str)
+Similar to @code{__builtin_nan}, except the return type is @code{_Decimal32}.
+@end deftypefn
+
+@deftypefn {Built-in Function} _Decimal64 __builtin_nand64 (const char *str)
+Similar to @code{__builtin_nan}, except the return type is @code{_Decimal64}.
+@end deftypefn
-This function, if given a string literal, is evaluated early enough
-that it is considered a compile-time constant.
+@deftypefn {Built-in Function} _Decimal128 __builtin_nand128 (const char *str)
+Similar to @code{__builtin_nan}, except the return type is @code{_Decimal128}.
@end deftypefn
@deftypefn {Built-in Function} float __builtin_nanf (const char *str)
@deftypefn {Built-in Function} double __builtin_nans (const char *str)
Similar to @code{__builtin_nan}, except the significand is forced
-to be a signaling NaN. The @code{nans} function is proposed by
+to be a signaling NaN@. The @code{nans} function is proposed by
@uref{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n965.htm,,WG14 N965}.
@end deftypefn
@end deftypefn
@deftypefn {Built-in Function} int __builtin_parity (unsigned int x)
-Returns the parity of @var{x}, i.@:e. the number of 1-bits in @var{x}
+Returns the parity of @var{x}, i.e.@: the number of 1-bits in @var{x}
modulo 2.
@end deftypefn
@code{unsigned long long}.
@end deftypefn
+@deftypefn {Built-in Function} double __builtin_powi (double, int)
+Returns the first argument raised to the power of the second. Unlike the
+@code{pow} function no guarantees about precision and rounding are made.
+@end deftypefn
+
+@deftypefn {Built-in Function} float __builtin_powif (float, int)
+Similar to @code{__builtin_powi}, except the argument and return types
+are @code{float}.
+@end deftypefn
+
+@deftypefn {Built-in Function} {long double} __builtin_powil (long double, int)
+Similar to @code{__builtin_powi}, except the argument and return types
+are @code{long double}.
+@end deftypefn
+
@node Target Builtins
@section Built-in Functions Specific to Particular Target Machines
@menu
* Alpha Built-in Functions::
* ARM Built-in Functions::
+* Blackfin Built-in Functions::
* FR-V Built-in Functions::
* X86 Built-in Functions::
+* MIPS DSP Built-in Functions::
* MIPS Paired-Single Support::
* PowerPC AltiVec Built-in Functions::
+* SPARC VIS Built-in Functions::
@end menu
@node Alpha Built-in Functions
long long __builtin_arm_wzero ()
@end smallexample
+@node Blackfin Built-in Functions
+@subsection Blackfin Built-in Functions
+
+Currently, there are two Blackfin-specific built-in functions. These are
+used for generating @code{CSYNC} and @code{SSYNC} machine insns without
+using inline assembly; by using these built-in functions the compiler can
+automatically add workarounds for hardware errata involving these
+instructions. These functions are named as follows:
+
+@smallexample
+void __builtin_bfin_csync (void)
+void __builtin_bfin_ssync (void)
+@end smallexample
+
@node FR-V Built-in Functions
@subsection FR-V Built-in Functions
* Argument Types::
* Directly-mapped Integer Functions::
* Directly-mapped Media Functions::
+* Raw read/write Functions::
* Other Built-in Functions::
@end menu
@tab @code{MXOR @var{a},@var{b},@var{c}}
@end multitable
+@node Raw read/write Functions
+@subsubsection Raw read/write Functions
+
+This sections describes built-in functions related to read and write
+instructions to access memory. These functions generate
+@code{membar} instructions to flush the I/O load and stores where
+appropriate, as described in Fujitsu's manual described above.
+
+@table @code
+
+@item unsigned char __builtin_read8 (void *@var{data})
+@item unsigned short __builtin_read16 (void *@var{data})
+@item unsigned long __builtin_read32 (void *@var{data})
+@item unsigned long long __builtin_read64 (void *@var{data})
+
+@item void __builtin_write8 (void *@var{data}, unsigned char @var{datum})
+@item void __builtin_write16 (void *@var{data}, unsigned short @var{datum})
+@item void __builtin_write32 (void *@var{data}, unsigned long @var{datum})
+@item void __builtin_write64 (void *@var{data}, unsigned long long @var{datum})
+@end table
+
@node Other Built-in Functions
@subsubsection Other Built-in Functions
These built-in functions are available for the i386 and x86-64 family
of computers, depending on the command-line switches used.
+Note that, if you specify command-line switches such as @option{-msse},
+the compiler could use the extended instruction sets even if the built-ins
+are not used explicitly in the program. For this reason, applications
+which perform runtime CPU detection must compile separate files for each
+supported architecture, using the appropriate flags. In particular,
+the file containing the CPU detection code should be compiled without
+these options.
+
The following machine modes are available for use with MMX built-in functions
(@pxref{Vector Extensions}): @code{V2SI} for a vector of two 32-bit integers,
@code{V4HI} for a vector of four 16-bit integers, and @code{V8QI} for a
v2si __builtin_ia32_pswapdsi (v2si)
@end smallexample
+@node MIPS DSP Built-in Functions
+@subsection MIPS DSP Built-in Functions
+
+The MIPS DSP Application-Specific Extension (ASE) includes new
+instructions that are designed to improve the performance of DSP and
+media applications. It provides instructions that operate on packed
+8-bit integer data, Q15 fractional data and Q31 fractional data.
+
+GCC supports MIPS DSP operations using both the generic
+vector extensions (@pxref{Vector Extensions}) and a collection of
+MIPS-specific built-in functions. Both kinds of support are
+enabled by the @option{-mdsp} command-line option.
+
+At present, GCC only provides support for operations on 32-bit
+vectors. The vector type associated with 8-bit integer data is
+usually called @code{v4i8} and the vector type associated with Q15 is
+usually called @code{v2q15}. They can be defined in C as follows:
+
+@smallexample
+typedef char v4i8 __attribute__ ((vector_size(4)));
+typedef short v2q15 __attribute__ ((vector_size(4)));
+@end smallexample
+
+@code{v4i8} and @code{v2q15} values are initialized in the same way as
+aggregates. For example:
+
+@smallexample
+v4i8 a = @{1, 2, 3, 4@};
+v4i8 b;
+b = (v4i8) @{5, 6, 7, 8@};
+
+v2q15 c = @{0x0fcb, 0x3a75@};
+v2q15 d;
+d = (v2q15) @{0.1234 * 0x1.0p15, 0.4567 * 0x1.0p15@};
+@end smallexample
+
+@emph{Note:} The CPU's endianness determines the order in which values
+are packed. On little-endian targets, the first value is the least
+significant and the last value is the most significant. The opposite
+order applies to big-endian targets. For example, the code above will
+set the lowest byte of @code{a} to @code{1} on little-endian targets
+and @code{4} on big-endian targets.
+
+@emph{Note:} Q15 and Q31 values must be initialized with their integer
+representation. As shown in this example, the integer representation
+of a Q15 value can be obtained by multiplying the fractional value by
+@code{0x1.0p15}. The equivalent for Q31 values is to multiply by
+@code{0x1.0p31}.
+
+The table below lists the @code{v4i8} and @code{v2q15} operations for which
+hardware support exists. @code{a} and @code{b} are @code{v4i8} values,
+and @code{c} and @code{d} are @code{v2q15} values.
+
+@multitable @columnfractions .50 .50
+@item C code @tab MIPS instruction
+@item @code{a + b} @tab @code{addu.qb}
+@item @code{c + d} @tab @code{addq.ph}
+@item @code{a - b} @tab @code{subu.qb}
+@item @code{c - d} @tab @code{subq.ph}
+@end multitable
+
+It is easier to describe the DSP built-in functions if we first define
+the following types:
+
+@smallexample
+typedef int q31;
+typedef int i32;
+typedef long long a64;
+@end smallexample
+
+@code{q31} and @code{i32} are actually the same as @code{int}, but we
+use @code{q31} to indicate a Q31 fractional value and @code{i32} to
+indicate a 32-bit integer value. Similarly, @code{a64} is the same as
+@code{long long}, but we use @code{a64} to indicate values that will
+be placed in one of the four DSP accumulators (@code{$ac0},
+@code{$ac1}, @code{$ac2} or @code{$ac3}).
+
+Also, some built-in functions prefer or require immediate numbers as
+parameters, because the corresponding DSP instructions accept both immediate
+numbers and register operands, or accept immediate numbers only. The
+immediate parameters are listed as follows.
+
+@smallexample
+imm0_7: 0 to 7.
+imm0_15: 0 to 15.
+imm0_31: 0 to 31.
+imm0_63: 0 to 63.
+imm0_255: 0 to 255.
+imm_n32_31: -32 to 31.
+imm_n512_511: -512 to 511.
+@end smallexample
+
+The following built-in functions map directly to a particular MIPS DSP
+instruction. Please refer to the architecture specification
+for details on what each instruction does.
+
+@smallexample
+v2q15 __builtin_mips_addq_ph (v2q15, v2q15)
+v2q15 __builtin_mips_addq_s_ph (v2q15, v2q15)
+q31 __builtin_mips_addq_s_w (q31, q31)
+v4i8 __builtin_mips_addu_qb (v4i8, v4i8)
+v4i8 __builtin_mips_addu_s_qb (v4i8, v4i8)
+v2q15 __builtin_mips_subq_ph (v2q15, v2q15)
+v2q15 __builtin_mips_subq_s_ph (v2q15, v2q15)
+q31 __builtin_mips_subq_s_w (q31, q31)
+v4i8 __builtin_mips_subu_qb (v4i8, v4i8)
+v4i8 __builtin_mips_subu_s_qb (v4i8, v4i8)
+i32 __builtin_mips_addsc (i32, i32)
+i32 __builtin_mips_addwc (i32, i32)
+i32 __builtin_mips_modsub (i32, i32)
+i32 __builtin_mips_raddu_w_qb (v4i8)
+v2q15 __builtin_mips_absq_s_ph (v2q15)
+q31 __builtin_mips_absq_s_w (q31)
+v4i8 __builtin_mips_precrq_qb_ph (v2q15, v2q15)
+v2q15 __builtin_mips_precrq_ph_w (q31, q31)
+v2q15 __builtin_mips_precrq_rs_ph_w (q31, q31)
+v4i8 __builtin_mips_precrqu_s_qb_ph (v2q15, v2q15)
+q31 __builtin_mips_preceq_w_phl (v2q15)
+q31 __builtin_mips_preceq_w_phr (v2q15)
+v2q15 __builtin_mips_precequ_ph_qbl (v4i8)
+v2q15 __builtin_mips_precequ_ph_qbr (v4i8)
+v2q15 __builtin_mips_precequ_ph_qbla (v4i8)
+v2q15 __builtin_mips_precequ_ph_qbra (v4i8)
+v2q15 __builtin_mips_preceu_ph_qbl (v4i8)
+v2q15 __builtin_mips_preceu_ph_qbr (v4i8)
+v2q15 __builtin_mips_preceu_ph_qbla (v4i8)
+v2q15 __builtin_mips_preceu_ph_qbra (v4i8)
+v4i8 __builtin_mips_shll_qb (v4i8, imm0_7)
+v4i8 __builtin_mips_shll_qb (v4i8, i32)
+v2q15 __builtin_mips_shll_ph (v2q15, imm0_15)
+v2q15 __builtin_mips_shll_ph (v2q15, i32)
+v2q15 __builtin_mips_shll_s_ph (v2q15, imm0_15)
+v2q15 __builtin_mips_shll_s_ph (v2q15, i32)
+q31 __builtin_mips_shll_s_w (q31, imm0_31)
+q31 __builtin_mips_shll_s_w (q31, i32)
+v4i8 __builtin_mips_shrl_qb (v4i8, imm0_7)
+v4i8 __builtin_mips_shrl_qb (v4i8, i32)
+v2q15 __builtin_mips_shra_ph (v2q15, imm0_15)
+v2q15 __builtin_mips_shra_ph (v2q15, i32)
+v2q15 __builtin_mips_shra_r_ph (v2q15, imm0_15)
+v2q15 __builtin_mips_shra_r_ph (v2q15, i32)
+q31 __builtin_mips_shra_r_w (q31, imm0_31)
+q31 __builtin_mips_shra_r_w (q31, i32)
+v2q15 __builtin_mips_muleu_s_ph_qbl (v4i8, v2q15)
+v2q15 __builtin_mips_muleu_s_ph_qbr (v4i8, v2q15)
+v2q15 __builtin_mips_mulq_rs_ph (v2q15, v2q15)
+q31 __builtin_mips_muleq_s_w_phl (v2q15, v2q15)
+q31 __builtin_mips_muleq_s_w_phr (v2q15, v2q15)
+a64 __builtin_mips_dpau_h_qbl (a64, v4i8, v4i8)
+a64 __builtin_mips_dpau_h_qbr (a64, v4i8, v4i8)
+a64 __builtin_mips_dpsu_h_qbl (a64, v4i8, v4i8)
+a64 __builtin_mips_dpsu_h_qbr (a64, v4i8, v4i8)
+a64 __builtin_mips_dpaq_s_w_ph (a64, v2q15, v2q15)
+a64 __builtin_mips_dpaq_sa_l_w (a64, q31, q31)
+a64 __builtin_mips_dpsq_s_w_ph (a64, v2q15, v2q15)
+a64 __builtin_mips_dpsq_sa_l_w (a64, q31, q31)
+a64 __builtin_mips_mulsaq_s_w_ph (a64, v2q15, v2q15)
+a64 __builtin_mips_maq_s_w_phl (a64, v2q15, v2q15)
+a64 __builtin_mips_maq_s_w_phr (a64, v2q15, v2q15)
+a64 __builtin_mips_maq_sa_w_phl (a64, v2q15, v2q15)
+a64 __builtin_mips_maq_sa_w_phr (a64, v2q15, v2q15)
+i32 __builtin_mips_bitrev (i32)
+i32 __builtin_mips_insv (i32, i32)
+v4i8 __builtin_mips_repl_qb (imm0_255)
+v4i8 __builtin_mips_repl_qb (i32)
+v2q15 __builtin_mips_repl_ph (imm_n512_511)
+v2q15 __builtin_mips_repl_ph (i32)
+void __builtin_mips_cmpu_eq_qb (v4i8, v4i8)
+void __builtin_mips_cmpu_lt_qb (v4i8, v4i8)
+void __builtin_mips_cmpu_le_qb (v4i8, v4i8)
+i32 __builtin_mips_cmpgu_eq_qb (v4i8, v4i8)
+i32 __builtin_mips_cmpgu_lt_qb (v4i8, v4i8)
+i32 __builtin_mips_cmpgu_le_qb (v4i8, v4i8)
+void __builtin_mips_cmp_eq_ph (v2q15, v2q15)
+void __builtin_mips_cmp_lt_ph (v2q15, v2q15)
+void __builtin_mips_cmp_le_ph (v2q15, v2q15)
+v4i8 __builtin_mips_pick_qb (v4i8, v4i8)
+v2q15 __builtin_mips_pick_ph (v2q15, v2q15)
+v2q15 __builtin_mips_packrl_ph (v2q15, v2q15)
+i32 __builtin_mips_extr_w (a64, imm0_31)
+i32 __builtin_mips_extr_w (a64, i32)
+i32 __builtin_mips_extr_r_w (a64, imm0_31)
+i32 __builtin_mips_extr_s_h (a64, i32)
+i32 __builtin_mips_extr_rs_w (a64, imm0_31)
+i32 __builtin_mips_extr_rs_w (a64, i32)
+i32 __builtin_mips_extr_s_h (a64, imm0_31)
+i32 __builtin_mips_extr_r_w (a64, i32)
+i32 __builtin_mips_extp (a64, imm0_31)
+i32 __builtin_mips_extp (a64, i32)
+i32 __builtin_mips_extpdp (a64, imm0_31)
+i32 __builtin_mips_extpdp (a64, i32)
+a64 __builtin_mips_shilo (a64, imm_n32_31)
+a64 __builtin_mips_shilo (a64, i32)
+a64 __builtin_mips_mthlip (a64, i32)
+void __builtin_mips_wrdsp (i32, imm0_63)
+i32 __builtin_mips_rddsp (imm0_63)
+i32 __builtin_mips_lbux (void *, i32)
+i32 __builtin_mips_lhx (void *, i32)
+i32 __builtin_mips_lwx (void *, i32)
+i32 __builtin_mips_bposge32 (void)
+@end smallexample
+
@node MIPS Paired-Single Support
@subsection MIPS Paired-Single Support
same type as the variable it is initializing.
@item
-If @code{signed} or @code{unsigned} is omitted, the vector type defaults
-to @code{signed} for @code{vector int} or @code{vector short} and to
-@code{unsigned} for @code{vector char}.
+If @code{signed} or @code{unsigned} is omitted, the signedness of the
+vector type is the default signedness of the base type. The default
+varies depending on the operating system, so a portable program should
+always specify the signedness.
@item
Compiling with @option{-maltivec} adds keywords @code{__vector},
int vec_any_out (vector float, vector float);
@end smallexample
+@node SPARC VIS Built-in Functions
+@subsection SPARC VIS Built-in Functions
+
+GCC supports SIMD operations on the SPARC using both the generic vector
+extensions (@pxref{Vector Extensions}) as well as built-in functions for
+the SPARC Visual Instruction Set (VIS). When you use the @option{-mvis}
+switch, the VIS extension is exposed as the following built-in functions:
+
+@smallexample
+typedef int v2si __attribute__ ((vector_size (8)));
+typedef short v4hi __attribute__ ((vector_size (8)));
+typedef short v2hi __attribute__ ((vector_size (4)));
+typedef char v8qi __attribute__ ((vector_size (8)));
+typedef char v4qi __attribute__ ((vector_size (4)));
+
+void * __builtin_vis_alignaddr (void *, long);
+int64_t __builtin_vis_faligndatadi (int64_t, int64_t);
+v2si __builtin_vis_faligndatav2si (v2si, v2si);
+v4hi __builtin_vis_faligndatav4hi (v4si, v4si);
+v8qi __builtin_vis_faligndatav8qi (v8qi, v8qi);
+
+v4hi __builtin_vis_fexpand (v4qi);
+
+v4hi __builtin_vis_fmul8x16 (v4qi, v4hi);
+v4hi __builtin_vis_fmul8x16au (v4qi, v4hi);
+v4hi __builtin_vis_fmul8x16al (v4qi, v4hi);
+v4hi __builtin_vis_fmul8sux16 (v8qi, v4hi);
+v4hi __builtin_vis_fmul8ulx16 (v8qi, v4hi);
+v2si __builtin_vis_fmuld8sux16 (v4qi, v2hi);
+v2si __builtin_vis_fmuld8ulx16 (v4qi, v2hi);
+
+v4qi __builtin_vis_fpack16 (v4hi);
+v8qi __builtin_vis_fpack32 (v2si, v2si);
+v2hi __builtin_vis_fpackfix (v2si);
+v8qi __builtin_vis_fpmerge (v4qi, v4qi);
+
+int64_t __builtin_vis_pdist (v8qi, v8qi, int64_t);
+@end smallexample
+
@node Target Format Checks
@section Format Checks Specific to Particular Target Machines
@menu
* ARM Pragmas::
+* M32C Pragmas::
* RS/6000 and PowerPC Pragmas::
* Darwin Pragmas::
* Solaris Pragmas::
* Symbol-Renaming Pragmas::
* Structure-Packing Pragmas::
+* Weak Pragmas::
+* Diagnostic Pragmas::
+* Visibility Pragmas::
@end menu
@node ARM Pragmas
subsequent functions.
@end table
+@node M32C Pragmas
+@subsection M32C Pragmas
+
+@table @code
+@item memregs @var{number}
+@cindex pragma, memregs
+Overrides the command line option @code{-memregs=} for the current
+file. Use with care! This pragma must be before any function in the
+file, and mixing different memregs values in different objects may
+make them incompatible. This pragma is useful when a
+performance-critical function uses a memreg for temporary values,
+as it may allow you to reduce the number of memregs used.
+
+@end table
+
@node RS/6000 and PowerPC Pragmas
@subsection RS/6000 and PowerPC Pragmas
Increase the minimum alignment of each @var{variable} to @var{alignment}.
This is the same as GCC's @code{aligned} attribute @pxref{Variable
-Attributes}).
+Attributes}). Macro expansion occurs on the arguments to this pragma
+when compiling C and Objective-C. It does not currently occur when
+compiling C++, but this is a bug which may be fixed in a future
+release.
@item fini (@var{function} [, @var{function}]...)
@cindex pragma, fini
This effect may be terminated with another @code{extern_prefix} pragma
whose argument is an empty string. The preprocessor macro
@code{__PRAGMA_EXTERN_PREFIX} will be defined if this pragma is
-available (currently only on Tru64 UNIX).
+available (currently only on Tru64 UNIX)@.
@end table
These pragmas and the asm labels extension interact in a complicated
@node Structure-Packing Pragmas
@subsection Structure-Packing Pragmas
-For compatibility with Win32, GCC supports as set of @code{#pragma}
-directives which change the maximum alignment of members of structures,
-unions, and classes subsequently defined. The @var{n} value below always
-is required to be a small power of two and specifies the new alignment
-in bytes.
+For compatibility with Win32, GCC supports a set of @code{#pragma}
+directives which change the maximum alignment of members of structures
+(other than zero-width bitfields), unions, and classes subsequently
+defined. The @var{n} value below always is required to be a small power
+of two and specifies the new alignment in bytes.
@enumerate
@item @code{#pragma pack(@var{n})} simply sets the new alignment.
@code{#pragma pack(pop)}.
@end enumerate
+Some targets, e.g. i386 and powerpc, support the @code{ms_struct}
+@code{#pragma} which lays out a structure as the documented
+@code{__attribute__ ((ms_struct))}.
+@enumerate
+@item @code{#pragma ms_struct on} turns on the layout for structures
+declared.
+@item @code{#pragma ms_struct off} turns off the layout for structures
+declared.
+@item @code{#pragma ms_struct reset} goes back to the default layout.
+@end enumerate
+
+@node Weak Pragmas
+@subsection Weak Pragmas
+
+For compatibility with SVR4, GCC supports a set of @code{#pragma}
+directives for declaring symbols to be weak, and defining weak
+aliases.
+
+@table @code
+@item #pragma weak @var{symbol}
+@cindex pragma, weak
+This pragma declares @var{symbol} to be weak, as if the declaration
+had the attribute of the same name. The pragma may appear before
+or after the declaration of @var{symbol}, but must appear before
+either its first use or its definition. It is not an error for
+@var{symbol} to never be defined at all.
+
+@item #pragma weak @var{symbol1} = @var{symbol2}
+This pragma declares @var{symbol1} to be a weak alias of @var{symbol2}.
+It is an error if @var{symbol2} is not defined in the current
+translation unit.
+@end table
+
+@node Diagnostic Pragmas
+@subsection Diagnostic Pragmas
+
+GCC allows the user to selectively enable or disable certain types of
+diagnostics, and change the kind of the diagnostic. For example, a
+project's policy might require that all sources compile with
+@option{-Werror} but certain files might have exceptions allowing
+specific types of warnings. Or, a project might selectively enable
+diagnostics and treat them as errors depending on which preprocessor
+macros are defined.
+
+@table @code
+@item #pragma GCC diagnostic @var{kind} @var{option}
+@cindex pragma, diagnostic
+
+Modifies the disposition of a diagnostic. Note that not all
+diagnostics are modifyiable; at the moment only warnings (normally
+controlled by @samp{-W...}) can be controlled, and not all of them.
+Use @option{-fdiagnostics-show-option} to determine which diagnostics
+are controllable and which option controls them.
+
+@var{kind} is @samp{error} to treat this diagnostic as an error,
+@samp{warning} to treat it like a warning (even if @option{-Werror} is
+in effect), or @samp{ignored} if the diagnostic is to be ignored.
+@var{option} is a double quoted string which matches the command line
+option.
+
+@example
+#pragma GCC diagnostic warning "-Wformat"
+#pragma GCC diagnostic error "-Walways-true"
+#pragma GCC diagnostic ignored "-Walways-true"
+@end example
+
+Note that these pragmas override any command line options. Also,
+while it is syntactically valid to put these pragmas anywhere in your
+sources, the only supported location for them is before any data or
+functions are defined. Doing otherwise may result in unpredictable
+results depending on how the optimizer manages your sources. If the
+same option is listed multiple times, the last one specified is the
+one that is in effect. This pragma is not intended to be a general
+purpose replacement for command line options, but for implementing
+strict control over project policies.
+
+@end table
+
+@node Visibility Pragmas
+@subsection Visibility Pragmas
+
+@table @code
+@item #pragma GCC visibility push(@var{visibility})
+@itemx #pragma GCC visibility pop
+@cindex pragma, visibility
+
+This pragma allows the user to set the visibility for multiple
+declarations without having to give each a visibility attribute
+@xref{Function Attributes}, for more information about visibility and
+the attribute syntax.
+
+In C++, @samp{#pragma GCC visibility} affects only namespace-scope
+declarations. Class members and template specializations are not
+affected; if you want to override the visibility for a particular
+member or instantiation, you must use an attribute.
+
+@end table
+
@node Unnamed Fields
@section Unnamed struct/union fields within structs/unions
@cindex struct
Predefined Macros,cpp,The GNU C Preprocessor}).
@menu
-* Min and Max:: C++ Minimum and maximum operators.
* Volatiles:: What constitutes an access to a volatile object.
* Restricted Pointers:: C99 restricted pointers and references.
* Vague Linkage:: Where G++ puts inlines, vtables and such.
* Bound member functions:: You can extract a function pointer to the
method denoted by a @samp{->*} or @samp{.*} expression.
* C++ Attributes:: Variable, function, and type attributes for C++ only.
-* Strong Using:: Strong using-directives for namespace composition.
+* Namespace Association:: Strong using-directives for namespace association.
* Java Exceptions:: Tweaking exception handling to work with Java.
* Deprecated Features:: Things will disappear from g++.
* Backwards Compatibility:: Compatibilities with earlier definitions of C++.
@end menu
-@node Min and Max
-@section Minimum and Maximum Operators in C++
-
-It is very convenient to have operators which return the ``minimum'' or the
-``maximum'' of two arguments. In GNU C++ (but not in GNU C),
-
-@table @code
-@item @var{a} <? @var{b}
-@findex <?
-@cindex minimum operator
-is the @dfn{minimum}, returning the smaller of the numeric values
-@var{a} and @var{b};
-
-@item @var{a} >? @var{b}
-@findex >?
-@cindex maximum operator
-is the @dfn{maximum}, returning the larger of the numeric values @var{a}
-and @var{b}.
-@end table
-
-These operations are not primitive in ordinary C++, since you can
-use a macro to return the minimum of two things in C++, as in the
-following example.
-
-@smallexample
-#define MIN(X,Y) ((X) < (Y) ? : (X) : (Y))
-@end smallexample
-
-@noindent
-You might then use @w{@samp{int min = MIN (i, j);}} to set @var{min} to
-the minimum value of variables @var{i} and @var{j}.
-
-However, side effects in @code{X} or @code{Y} may cause unintended
-behavior. For example, @code{MIN (i++, j++)} will fail, incrementing
-the smaller counter twice. The GNU C @code{typeof} extension allows you
-to write safe macros that avoid this kind of problem (@pxref{Typeof}).
-However, writing @code{MIN} and @code{MAX} as macros also forces you to
-use function-call notation for a fundamental arithmetic operation.
-Using GNU C++ extensions, you can write @w{@samp{int min = i <? j;}}
-instead.
-
-Since @code{<?} and @code{>?} are built into the compiler, they properly
-handle expressions with side-effects; @w{@samp{int min = i++ <? j++;}}
-works correctly.
-
@node Volatiles
@section When is a Volatile Object Accessed?
@cindex accessing volatiles
@end table
-See also @xref{Strong Using}.
+See also @xref{Namespace Association}.
-@node Strong Using
-@section Strong Using
+@node Namespace Association
+@section Namespace Association
@strong{Caution:} The semantics of this extension are not fully
defined. Users should refrain from using this extension as its
semantics may change subtly over time. It is possible that this
-extension wil be removed in future versions of G++.
+extension will be removed in future versions of G++.
A using-directive with @code{__attribute ((strong))} is stronger
than a normal using-directive in two ways:
@itemize @bullet
@item
-Templates from the used namespace can be specialized as though they were members of the using namespace.
+Templates from the used namespace can be specialized and explicitly
+instantiated as though they were members of the using namespace.
@item
The using namespace is considered an associated namespace of all
name lookup.
@end itemize
+The used namespace must be nested within the using namespace so that
+normal unqualified lookup works properly.
+
This is useful for composing a namespace transparently from
implementation namespaces. For example:
it is required for backwards compatibility @xref{Backwards Compatibility}.
@end table
+G++ allows a virtual function returning @samp{void *} to be overridden
+by one returning a different pointer type. This extension to the
+covariant return type rules is now deprecated and will be removed from a
+future version.
+
+The G++ minimum and maximum operators (@samp{<?} and @samp{>?}) and
+their compound forms (@samp{<?=}) and @samp{>?=}) have been deprecated
+and will be removed in a future version. Code using these operators
+should be modified to use @code{std::min} and @code{std::max} instead.
+
The named return value extension has been deprecated, and is now
removed from G++.
and other places where they are not permitted by the standard is
deprecated and will be removed from a future version of G++.
+G++ allows floating-point literals to appear in integral constant expressions,
+e.g. @samp{ enum E @{ e = int(2.2 * 3.7) @} }
+This extension is deprecated and will be removed from a future version.
+
+G++ allows static data members of const floating-point type to be declared
+with an initializer in a class definition. The standard only allows
+initializers for static members of const integral types and const
+enumeration types so this extension has been deprecated and will be removed
+from a future version.
+
@node Backwards Compatibility
@section Backwards Compatibility
@cindex Backwards Compatibility
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