1 /* Specialized bits of code needed to support construction and
2 destruction of file-scope objects in C++ code.
3 Copyright (C) 1991, 1994-1999 Free Software Foundation, Inc.
4 Contributed by Ron Guilmette (rfg@monkeys.com).
6 This file is part of GNU CC.
8 GNU CC is free software; you can redistribute it and/or modify
9 it under the terms of the GNU General Public License as published by
10 the Free Software Foundation; either version 2, or (at your option)
13 GNU CC is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 GNU General Public License for more details.
18 You should have received a copy of the GNU General Public License
19 along with GNU CC; see the file COPYING. If not, write to
20 the Free Software Foundation, 59 Temple Place - Suite 330,
21 Boston, MA 02111-1307, USA. */
23 /* As a special exception, if you link this library with files
24 compiled with GCC to produce an executable, this does not cause
25 the resulting executable to be covered by the GNU General Public License.
26 This exception does not however invalidate any other reasons why
27 the executable file might be covered by the GNU General Public License. */
29 /* This file is a bit like libgcc1.c/libgcc2.c in that it is compiled
30 multiple times and yields multiple .o files.
32 This file is useful on target machines where the object file format
33 supports multiple "user-defined" sections (e.g. COFF, ELF, ROSE). On
34 such systems, this file allows us to avoid running collect (or any
35 other such slow and painful kludge). Additionally, if the target
36 system supports a .init section, this file allows us to support the
37 linking of C++ code with a non-C++ main program.
39 Note that if INIT_SECTION_ASM_OP is defined in the tm.h file, then
40 this file *will* make use of the .init section. If that symbol is
41 not defined however, then the .init section will not be used.
43 Currently, only ELF and COFF are supported. It is likely however that
44 ROSE could also be supported, if someone was willing to do the work to
45 make whatever (small?) adaptations are needed. (Some work may be
46 needed on the ROSE assembler and linker also.)
48 This file must be compiled with gcc. */
50 /* It is incorrect to include config.h here, because this file is being
51 compiled for the target, and hence definitions concerning only the host
59 /* We do not want to add the weak attribute to the declarations of these
60 routines in frame.h because that will cause the definition of these
61 symbols to be weak as well.
63 This exposes a core issue, how to handle creating weak references vs
64 how to create weak definitions. Either we have to have the definition
65 of TARGET_WEAK_ATTRIBUTE be conditional in the shared header files or
66 have a second declaration if we want a function's references to be weak,
67 but not its definition.
69 Making TARGET_WEAK_ATTRIBUTE conditional seems like a good solution until
70 one thinks about scaling to larger problems -- ie, the condition under
71 which TARGET_WEAK_ATTRIBUTE is active will eventually get far too
74 So, we take an approach similar to #pragma weak -- we have a second
75 declaration for functions that we want to have weak references.
77 Neither way is particularly good. */
79 /* References to __register_frame_info and __deregister_frame_info should
80 be weak in this file if at all possible. */
81 extern void __register_frame_info (void *, struct object *)
82 TARGET_ATTRIBUTE_WEAK;
84 extern void *__deregister_frame_info (void *)
85 TARGET_ATTRIBUTE_WEAK;
87 #ifndef OBJECT_FORMAT_MACHO
89 /* Provide default definitions for the pseudo-ops used to switch to the
90 .ctors and .dtors sections.
92 Note that we want to give these sections the SHF_WRITE attribute
93 because these sections will actually contain data (i.e. tables of
94 addresses of functions in the current root executable or shared library
95 file) and, in the case of a shared library, the relocatable addresses
96 will have to be properly resolved/relocated (and then written into) by
97 the dynamic linker when it actually attaches the given shared library
98 to the executing process. (Note that on SVR4, you may wish to use the
99 `-z text' option to the ELF linker, when building a shared library, as
100 an additional check that you are doing everything right. But if you do
101 use the `-z text' option when building a shared library, you will get
102 errors unless the .ctors and .dtors sections are marked as writable
103 via the SHF_WRITE attribute.) */
105 #ifndef CTORS_SECTION_ASM_OP
106 #define CTORS_SECTION_ASM_OP ".section\t.ctors,\"aw\""
108 #ifndef DTORS_SECTION_ASM_OP
109 #define DTORS_SECTION_ASM_OP ".section\t.dtors,\"aw\""
112 #ifdef OBJECT_FORMAT_ELF
114 /* Declare a pointer to void function type. */
115 typedef void (*func_ptr) (void);
116 #define STATIC static
118 #else /* OBJECT_FORMAT_ELF */
120 #include "gbl-ctors.h"
124 #endif /* OBJECT_FORMAT_ELF */
128 #ifdef INIT_SECTION_ASM_OP
130 #ifdef OBJECT_FORMAT_ELF
132 /* Declare the __dso_handle variable. It should have a unique value
133 in every shared-object; in a main program its value is zero. */
136 void *__dso_handle = &__dso_handle;
138 void *__dso_handle = 0;
141 /* The __cxa_finalize function may not be available so we use only a
143 extern void __cxa_finalize (void *) TARGET_ATTRIBUTE_WEAK;
145 /* Run all the global destructors on exit from the program. */
147 /* Some systems place the number of pointers in the first word of the
148 table. On SVR4 however, that word is -1. In all cases, the table is
149 null-terminated. On SVR4, we start from the beginning of the list and
150 invoke each per-compilation-unit destructor routine in order
151 until we find that null.
153 Note that this function MUST be static. There will be one of these
154 functions in each root executable and one in each shared library, but
155 although they all have the same code, each one is unique in that it
156 refers to one particular associated `__DTOR_LIST__' which belongs to the
157 same particular root executable or shared library file.
159 On some systems, this routine is run more than once from the .fini,
160 when exit is called recursively, so we arrange to remember where in
161 the list we left off processing, and we resume at that point,
162 should we be re-invoked. */
164 static char __EH_FRAME_BEGIN__[];
165 static func_ptr __DTOR_LIST__[];
167 __do_global_dtors_aux (void)
169 static func_ptr *p = __DTOR_LIST__ + 1;
170 static int completed = 0;
177 __cxa_finalize (__dso_handle);
186 #ifdef EH_FRAME_SECTION_ASM_OP
187 if (__deregister_frame_info)
188 __deregister_frame_info (__EH_FRAME_BEGIN__);
194 /* Stick a call to __do_global_dtors_aux into the .fini section. */
196 static void __attribute__ ((__unused__))
199 asm (FINI_SECTION_ASM_OP);
200 __do_global_dtors_aux ();
201 #ifdef FORCE_FINI_SECTION_ALIGN
202 FORCE_FINI_SECTION_ALIGN;
204 asm (TEXT_SECTION_ASM_OP);
207 #ifdef EH_FRAME_SECTION_ASM_OP
208 /* Stick a call to __register_frame_info into the .init section. For some
209 reason calls with no arguments work more reliably in .init, so stick the
210 call in another function. */
215 static struct object object;
216 if (__register_frame_info)
217 __register_frame_info (__EH_FRAME_BEGIN__, &object);
220 static void __attribute__ ((__unused__))
223 asm (INIT_SECTION_ASM_OP);
225 #ifdef FORCE_INIT_SECTION_ALIGN
226 FORCE_INIT_SECTION_ALIGN;
228 asm (TEXT_SECTION_ASM_OP);
230 #endif /* EH_FRAME_SECTION_ASM_OP */
232 #else /* OBJECT_FORMAT_ELF */
234 /* The function __do_global_ctors_aux is compiled twice (once in crtbegin.o
235 and once in crtend.o). It must be declared static to avoid a link
236 error. Here, we define __do_global_ctors as an externally callable
237 function. It is externally callable so that __main can invoke it when
238 INVOKE__main is defined. This has the additional effect of forcing cc1
239 to switch to the .text section. */
241 static void __do_global_ctors_aux ();
243 __do_global_ctors (void)
245 #ifdef INVOKE__main /* If __main won't actually call __do_global_ctors
246 then it doesn't matter what's inside the function.
247 The inside of __do_global_ctors_aux is called
248 automatically in that case.
249 And the Alliant fx2800 linker crashes
250 on this reference. So prevent the crash. */
251 __do_global_ctors_aux ();
255 asm (INIT_SECTION_ASM_OP); /* cc1 doesn't know that we are switching! */
257 /* On some svr4 systems, the initial .init section preamble code provided in
258 crti.o may do something, such as bump the stack, which we have to
259 undo before we reach the function prologue code for __do_global_ctors
260 (directly below). For such systems, define the macro INIT_SECTION_PREAMBLE
261 to expand into the code needed to undo the actions of the crti.o file. */
263 #ifdef INIT_SECTION_PREAMBLE
264 INIT_SECTION_PREAMBLE;
267 /* A routine to invoke all of the global constructors upon entry to the
268 program. We put this into the .init section (for systems that have
269 such a thing) so that we can properly perform the construction of
270 file-scope static-storage C++ objects within shared libraries. */
273 __do_global_ctors_aux (void) /* prologue goes in .init section */
275 #ifdef FORCE_INIT_SECTION_ALIGN
276 FORCE_INIT_SECTION_ALIGN; /* Explicit align before switch to .text */
278 asm (TEXT_SECTION_ASM_OP); /* don't put epilogue and body in .init */
279 DO_GLOBAL_CTORS_BODY;
280 atexit (__do_global_dtors);
283 #endif /* OBJECT_FORMAT_ELF */
285 #else /* defined(INIT_SECTION_ASM_OP) */
287 #ifdef HAS_INIT_SECTION
288 /* This case is used by the Irix 6 port, which supports named sections but
289 not an SVR4-style .fini section. __do_global_dtors can be non-static
290 in this case because we protect it with -hidden_symbol. */
292 static char __EH_FRAME_BEGIN__[];
293 static func_ptr __DTOR_LIST__[];
295 __do_global_dtors (void)
298 for (p = __DTOR_LIST__ + 1; *p; p++)
301 #ifdef EH_FRAME_SECTION_ASM_OP
302 if (__deregister_frame_info)
303 __deregister_frame_info (__EH_FRAME_BEGIN__);
307 #ifdef EH_FRAME_SECTION_ASM_OP
308 /* Define a function here to call __register_frame. crtend.o is linked in
309 after libgcc.a, and hence can't call libgcc.a functions directly. That
310 can lead to unresolved function references. */
314 static struct object object;
315 if (__register_frame_info)
316 __register_frame_info (__EH_FRAME_BEGIN__, &object);
321 #endif /* defined(INIT_SECTION_ASM_OP) */
323 /* Force cc1 to switch to .data section. */
324 static func_ptr force_to_data[0] __attribute__ ((__unused__)) = { };
326 /* NOTE: In order to be able to support SVR4 shared libraries, we arrange
327 to have one set of symbols { __CTOR_LIST__, __DTOR_LIST__, __CTOR_END__,
328 __DTOR_END__ } per root executable and also one set of these symbols
329 per shared library. So in any given whole process image, we may have
330 multiple definitions of each of these symbols. In order to prevent
331 these definitions from conflicting with one another, and in order to
332 ensure that the proper lists are used for the initialization/finalization
333 of each individual shared library (respectively), we give these symbols
334 only internal (i.e. `static') linkage, and we also make it a point to
335 refer to only the __CTOR_END__ symbol in crtend.o and the __DTOR_LIST__
336 symbol in crtbegin.o, where they are defined. */
338 /* The -1 is a flag to __do_global_[cd]tors
339 indicating that this table does not start with a count of elements. */
340 #ifdef CTOR_LIST_BEGIN
343 asm (CTORS_SECTION_ASM_OP); /* cc1 doesn't know that we are switching! */
344 STATIC func_ptr __CTOR_LIST__[1] __attribute__ ((__unused__))
345 = { (func_ptr) (-1) };
348 #ifdef DTOR_LIST_BEGIN
351 asm (DTORS_SECTION_ASM_OP); /* cc1 doesn't know that we are switching! */
352 STATIC func_ptr __DTOR_LIST__[1] = { (func_ptr) (-1) };
355 #ifdef EH_FRAME_SECTION_ASM_OP
356 /* Stick a label at the beginning of the frame unwind info so we can register
357 and deregister it with the exception handling library code. */
359 asm (EH_FRAME_SECTION_ASM_OP);
360 #ifdef INIT_SECTION_ASM_OP
363 char __EH_FRAME_BEGIN__[] = { };
364 #endif /* EH_FRAME_SECTION_ASM_OP */
366 #endif /* defined(CRT_BEGIN) */
370 #ifdef INIT_SECTION_ASM_OP
372 #ifdef OBJECT_FORMAT_ELF
374 static func_ptr __CTOR_END__[];
376 __do_global_ctors_aux (void)
379 for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
383 /* Stick a call to __do_global_ctors_aux into the .init section. */
385 static void __attribute__ ((__unused__))
388 asm (INIT_SECTION_ASM_OP);
389 __do_global_ctors_aux ();
390 #ifdef FORCE_INIT_SECTION_ALIGN
391 FORCE_INIT_SECTION_ALIGN;
393 asm (TEXT_SECTION_ASM_OP);
395 /* This is a kludge. The i386 GNU/Linux dynamic linker needs ___brk_addr,
396 __environ and atexit (). We have to make sure they are in the .dynsym
397 section. We accomplish it by making a dummy call here. This
398 code is never reached. */
400 #if defined(__linux__) && defined(__PIC__) && defined(__i386__)
402 extern void *___brk_addr;
403 extern char **__environ;
405 ___brk_addr = __environ;
411 #else /* OBJECT_FORMAT_ELF */
413 /* Stick the real initialization code, followed by a normal sort of
414 function epilogue at the very end of the .init section for this
415 entire root executable file or for this entire shared library file.
417 Note that we use some tricks here to get *just* the body and just
418 a function epilogue (but no function prologue) into the .init
419 section of the crtend.o file. Specifically, we switch to the .text
420 section, start to define a function, and then we switch to the .init
421 section just before the body code.
423 Earlier on, we put the corresponding function prologue into the .init
424 section of the crtbegin.o file (which will be linked in first).
426 Note that we want to invoke all constructors for C++ file-scope static-
427 storage objects AFTER any other possible initialization actions which
428 may be performed by the code in the .init section contributions made by
429 other libraries, etc. That's because those other initializations may
430 include setup operations for very primitive things (e.g. initializing
431 the state of the floating-point coprocessor, etc.) which should be done
432 before we start to execute any of the user's code. */
435 __do_global_ctors_aux (void) /* prologue goes in .text section */
437 asm (INIT_SECTION_ASM_OP);
438 DO_GLOBAL_CTORS_BODY;
439 atexit (__do_global_dtors);
440 } /* epilogue and body go in .init section */
442 #ifdef FORCE_INIT_SECTION_ALIGN
443 FORCE_INIT_SECTION_ALIGN;
446 asm (TEXT_SECTION_ASM_OP);
448 #endif /* OBJECT_FORMAT_ELF */
450 #else /* defined(INIT_SECTION_ASM_OP) */
452 #ifdef HAS_INIT_SECTION
453 /* This case is used by the Irix 6 port, which supports named sections but
454 not an SVR4-style .init section. __do_global_ctors can be non-static
455 in this case because we protect it with -hidden_symbol. */
456 static func_ptr __CTOR_END__[];
457 #ifdef EH_FRAME_SECTION_ASM_OP
458 extern void __frame_dummy (void);
461 __do_global_ctors (void)
464 #ifdef EH_FRAME_SECTION_ASM_OP
467 for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
472 #endif /* defined(INIT_SECTION_ASM_OP) */
474 /* Force cc1 to switch to .data section. */
475 static func_ptr force_to_data[0] __attribute__ ((__unused__)) = { };
477 /* Put a word containing zero at the end of each of our two lists of function
478 addresses. Note that the words defined here go into the .ctors and .dtors
479 sections of the crtend.o file, and since that file is always linked in
480 last, these words naturally end up at the very ends of the two lists
481 contained in these two sections. */
486 asm (CTORS_SECTION_ASM_OP); /* cc1 doesn't know that we are switching! */
487 STATIC func_ptr __CTOR_END__[1] = { (func_ptr) 0 };
493 asm (DTORS_SECTION_ASM_OP); /* cc1 doesn't know that we are switching! */
494 STATIC func_ptr __DTOR_END__[1] __attribute__ ((__unused__))
498 #ifdef EH_FRAME_SECTION_ASM_OP
499 /* Terminate the frame unwind info section with a 4byte 0 as a sentinel;
500 this would be the 'length' field in a real FDE. */
502 typedef unsigned int ui32 __attribute__ ((mode (SI)));
503 asm (EH_FRAME_SECTION_ASM_OP);
504 STATIC ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
505 #endif /* EH_FRAME_SECTION */
507 #endif /* defined(CRT_END) */
509 #else /* OBJECT_FORMAT_MACHO */
511 /* For Mach-O format executables, we assume that the system's runtime is
512 smart enough to handle constructors and destructors, but doesn't have
513 an init section (if it can't even handle constructors/destructors
514 you should be using INVOKE__main, not crtstuff). All we need to do
515 is install/deinstall the frame information for exceptions. We do this
516 by putting a constructor in crtbegin.o and a destructor in crtend.o.
518 crtend.o also puts in the terminating zero in the frame information
521 /* The crtstuff for other object formats use the symbol __EH_FRAME_BEGIN__
522 to figure out the start of the exception frame, but here we use
523 getsectbynamefromheader to find this value. Either method would work,
524 but this method avoids creating any global symbols, which seems
527 #include <mach-o/ldsyms.h>
528 extern const struct section *
529 getsectbynamefromheader (const struct mach_header *,
530 const char *, const char *);
534 static void __reg_frame_ctor () __attribute__ ((constructor));
537 __reg_frame_ctor (void)
539 static struct object object;
540 const struct section *eh_frame;
542 eh_frame = getsectbynamefromheader (&_mh_execute_header,
543 "__TEXT", "__eh_frame");
544 __register_frame_info ((void *) eh_frame->addr, &object);
547 #endif /* CRT_BEGIN */
551 static void __dereg_frame_dtor () __attribute__ ((destructor));
555 __dereg_frame_dtor (void)
557 const struct section *eh_frame;
559 eh_frame = getsectbynamefromheader (&_mh_execute_header,
560 "__TEXT", "__eh_frame");
561 __deregister_frame_info ((void *) eh_frame->addr);
564 /* Terminate the frame section with a final zero. */
566 /* Force cc1 to switch to .data section. */
567 static void * force_to_data[0] __attribute__ ((__unused__)) = { };
569 typedef unsigned int ui32 __attribute__ ((mode (SI)));
570 asm (EH_FRAME_SECTION_ASM_OP);
571 static ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
575 #endif /* OBJECT_FORMAT_MACHO */