-fallow-single-precision -fcond-mismatch @gol
-fsigned-bitfields -fsigned-char @gol
-funsigned-bitfields -funsigned-char @gol
--fwritable-strings -fshort-wchar}
+-fwritable-strings}
@item C++ Language Options
@xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
-fno-common -fno-ident -fno-gnu-linker @gol
-fpcc-struct-return -fpic -fPIC @gol
-freg-struct-return -fshared-data -fshort-enums @gol
--fshort-double -fvolatile @gol
+-fshort-double -fshort-wchar -fvolatile @gol
-fvolatile-global -fvolatile-static @gol
-fverbose-asm -fpack-struct -fstack-check @gol
-fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
Writing into string constants is a very bad idea; ``constants'' should
be constant.
-
-@item -fshort-wchar
-@opindex fshort-wchar
-Override the underlying type for @samp{wchar_t} to be @samp{short
-unsigned int} instead of the default for the target. This option is
-useful for building programs to run under WINE@.
@end table
@node C++ Dialect Options
Return ``short'' @code{struct} and @code{union} values in memory like
longer ones, rather than in registers. This convention is less
efficient, but it has the advantage of allowing intercallability between
-GCC-compiled files and files compiled with other compilers.
+GCC-compiled files and files compiled with other compilers, particularly
+the Portable C Compiler (pcc).
The precise convention for returning structures in memory depends
on the target configuration macros.
Short structures and unions are those whose size and alignment match
that of some integer type.
+@strong{Warning:} code compiled with the @option{-fpcc-struct-return}
+switch is not binary compatible with code compiled with the
+@option{-freg-struct-return} switch.
+Use it to conform to a non-default application binary interface.
+
@item -freg-struct-return
@opindex freg-struct-return
Return @code{struct} and @code{union} values in registers when possible.
the principal compiler. In those cases, we can choose the standard, and
we chose the more efficient register return alternative.
+@strong{Warning:} code compiled with the @option{-freg-struct-return}
+switch is not binary compatible with code compiled with the
+@option{-fpcc-struct-return} switch.
+Use it to conform to a non-default application binary interface.
+
@item -fshort-enums
@opindex fshort-enums
Allocate to an @code{enum} type only as many bytes as it needs for the
declared range of possible values. Specifically, the @code{enum} type
will be equivalent to the smallest integer type which has enough room.
+@strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
+code that is not binary compatible with code generated without that switch.
+Use it to conform to a non-default application binary interface.
+
@item -fshort-double
@opindex fshort-double
Use the same size for @code{double} as for @code{float}.
+@strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
+code that is not binary compatible with code generated without that switch.
+Use it to conform to a non-default application binary interface.
+
+@item -fshort-wchar
+@opindex fshort-wchar
+Override the underlying type for @samp{wchar_t} to be @samp{short
+unsigned int} instead of the default for the target. This option is
+useful for building programs to run under WINE@.
+
+@strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
+code that is not binary compatible with code generated without that switch.
+Use it to conform to a non-default application binary interface.
+
@item -fshared-data
@opindex fshared-data
Requests that the data and non-@code{const} variables of this
@item -fpack-struct
@opindex fpack-struct
-Pack all structure members together without holes. Usually you would
-not want to use this option, since it makes the code suboptimal, and
-the offsets of structure members won't agree with system libraries.
+Pack all structure members together without holes.
+
+@strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
+code that is not binary compatible with code generated without that switch.
+Additionally, it makes the code suboptimial.
+Use it to conform to a non-default application binary interface.
@item -finstrument-functions
@opindex finstrument-functions
change the way C symbols are represented in the object file. One use
is to help link with legacy assembly code.
-Be warned that you should know what you are doing when invoking this
-option, and that not all targets provide complete support for it.
+@strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
+generate code that is not binary compatible with code generated without that
+switch. Use it to conform to a non-default application binary interface.
+Not all targets provide complete support for this switch.
@item -ftls-model=@var{model}
Alter the thread-local storage model to be used (@pxref{Thread-Local}).
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