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"
123 #define ON_EXIT(a, b)
127 #endif /* OBJECT_FORMAT_ELF */
131 #ifdef INIT_SECTION_ASM_OP
133 #ifdef OBJECT_FORMAT_ELF
135 /* Run all the global destructors on exit from the program. */
137 /* Some systems place the number of pointers in the first word of the
138 table. On SVR4 however, that word is -1. In all cases, the table is
139 null-terminated. On SVR4, we start from the beginning of the list and
140 invoke each per-compilation-unit destructor routine in order
141 until we find that null.
143 Note that this function MUST be static. There will be one of these
144 functions in each root executable and one in each shared library, but
145 although they all have the same code, each one is unique in that it
146 refers to one particular associated `__DTOR_LIST__' which belongs to the
147 same particular root executable or shared library file.
149 On some systems, this routine is run more than once from the .fini,
150 when exit is called recursively, so we arrange to remember where in
151 the list we left off processing, and we resume at that point,
152 should we be re-invoked. */
154 static char __EH_FRAME_BEGIN__[];
155 static func_ptr __DTOR_LIST__[];
157 __do_global_dtors_aux (void)
159 static func_ptr *p = __DTOR_LIST__ + 1;
160 static int completed = 0;
171 #ifdef EH_FRAME_SECTION_ASM_OP
172 if (__deregister_frame_info)
173 __deregister_frame_info (__EH_FRAME_BEGIN__);
179 /* Stick a call to __do_global_dtors_aux into the .fini section. */
181 static void __attribute__ ((__unused__))
184 asm (FINI_SECTION_ASM_OP);
185 __do_global_dtors_aux ();
186 #ifdef FORCE_FINI_SECTION_ALIGN
187 FORCE_FINI_SECTION_ALIGN;
189 asm (TEXT_SECTION_ASM_OP);
192 #ifdef EH_FRAME_SECTION_ASM_OP
193 /* Stick a call to __register_frame_info into the .init section. For some
194 reason calls with no arguments work more reliably in .init, so stick the
195 call in another function. */
200 static struct object object;
201 if (__register_frame_info)
202 __register_frame_info (__EH_FRAME_BEGIN__, &object);
205 static void __attribute__ ((__unused__))
208 asm (INIT_SECTION_ASM_OP);
210 #ifdef FORCE_INIT_SECTION_ALIGN
211 FORCE_INIT_SECTION_ALIGN;
213 asm (TEXT_SECTION_ASM_OP);
215 #endif /* EH_FRAME_SECTION_ASM_OP */
217 #else /* OBJECT_FORMAT_ELF */
219 /* The function __do_global_ctors_aux is compiled twice (once in crtbegin.o
220 and once in crtend.o). It must be declared static to avoid a link
221 error. Here, we define __do_global_ctors as an externally callable
222 function. It is externally callable so that __main can invoke it when
223 INVOKE__main is defined. This has the additional effect of forcing cc1
224 to switch to the .text section. */
226 static void __do_global_ctors_aux ();
228 __do_global_ctors (void)
230 #ifdef INVOKE__main /* If __main won't actually call __do_global_ctors
231 then it doesn't matter what's inside the function.
232 The inside of __do_global_ctors_aux is called
233 automatically in that case.
234 And the Alliant fx2800 linker crashes
235 on this reference. So prevent the crash. */
236 __do_global_ctors_aux ();
240 asm (INIT_SECTION_ASM_OP); /* cc1 doesn't know that we are switching! */
242 /* On some svr4 systems, the initial .init section preamble code provided in
243 crti.o may do something, such as bump the stack, which we have to
244 undo before we reach the function prologue code for __do_global_ctors
245 (directly below). For such systems, define the macro INIT_SECTION_PREAMBLE
246 to expand into the code needed to undo the actions of the crti.o file. */
248 #ifdef INIT_SECTION_PREAMBLE
249 INIT_SECTION_PREAMBLE;
252 /* A routine to invoke all of the global constructors upon entry to the
253 program. We put this into the .init section (for systems that have
254 such a thing) so that we can properly perform the construction of
255 file-scope static-storage C++ objects within shared libraries. */
258 __do_global_ctors_aux (void) /* prologue goes in .init section */
260 #ifdef FORCE_INIT_SECTION_ALIGN
261 FORCE_INIT_SECTION_ALIGN; /* Explicit align before switch to .text */
263 asm (TEXT_SECTION_ASM_OP); /* don't put epilogue and body in .init */
264 DO_GLOBAL_CTORS_BODY;
265 ON_EXIT (__do_global_dtors, 0);
268 #endif /* OBJECT_FORMAT_ELF */
270 #else /* defined(INIT_SECTION_ASM_OP) */
272 #ifdef HAS_INIT_SECTION
273 /* This case is used by the Irix 6 port, which supports named sections but
274 not an SVR4-style .fini section. __do_global_dtors can be non-static
275 in this case because we protect it with -hidden_symbol. */
277 static char __EH_FRAME_BEGIN__[];
278 static func_ptr __DTOR_LIST__[];
280 __do_global_dtors (void)
283 for (p = __DTOR_LIST__ + 1; *p; p++)
286 #ifdef EH_FRAME_SECTION_ASM_OP
287 if (__deregister_frame_info)
288 __deregister_frame_info (__EH_FRAME_BEGIN__);
292 #ifdef EH_FRAME_SECTION_ASM_OP
293 /* Define a function here to call __register_frame. crtend.o is linked in
294 after libgcc.a, and hence can't call libgcc.a functions directly. That
295 can lead to unresolved function references. */
299 static struct object object;
300 if (__register_frame_info)
301 __register_frame_info (__EH_FRAME_BEGIN__, &object);
306 #endif /* defined(INIT_SECTION_ASM_OP) */
308 /* Force cc1 to switch to .data section. */
309 static func_ptr force_to_data[0] __attribute__ ((__unused__)) = { };
311 /* NOTE: In order to be able to support SVR4 shared libraries, we arrange
312 to have one set of symbols { __CTOR_LIST__, __DTOR_LIST__, __CTOR_END__,
313 __DTOR_END__ } per root executable and also one set of these symbols
314 per shared library. So in any given whole process image, we may have
315 multiple definitions of each of these symbols. In order to prevent
316 these definitions from conflicting with one another, and in order to
317 ensure that the proper lists are used for the initialization/finalization
318 of each individual shared library (respectively), we give these symbols
319 only internal (i.e. `static') linkage, and we also make it a point to
320 refer to only the __CTOR_END__ symbol in crtend.o and the __DTOR_LIST__
321 symbol in crtbegin.o, where they are defined. */
323 /* The -1 is a flag to __do_global_[cd]tors
324 indicating that this table does not start with a count of elements. */
325 #ifdef CTOR_LIST_BEGIN
328 asm (CTORS_SECTION_ASM_OP); /* cc1 doesn't know that we are switching! */
329 STATIC func_ptr __CTOR_LIST__[1] __attribute__ ((__unused__))
330 = { (func_ptr) (-1) };
333 #ifdef DTOR_LIST_BEGIN
336 asm (DTORS_SECTION_ASM_OP); /* cc1 doesn't know that we are switching! */
337 STATIC func_ptr __DTOR_LIST__[1] = { (func_ptr) (-1) };
340 #ifdef EH_FRAME_SECTION_ASM_OP
341 /* Stick a label at the beginning of the frame unwind info so we can register
342 and deregister it with the exception handling library code. */
344 asm (EH_FRAME_SECTION_ASM_OP);
345 #ifdef INIT_SECTION_ASM_OP
348 char __EH_FRAME_BEGIN__[] = { };
349 #endif /* EH_FRAME_SECTION_ASM_OP */
351 #endif /* defined(CRT_BEGIN) */
355 #ifdef INIT_SECTION_ASM_OP
357 #ifdef OBJECT_FORMAT_ELF
359 static func_ptr __CTOR_END__[];
361 __do_global_ctors_aux (void)
364 for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
368 /* Stick a call to __do_global_ctors_aux into the .init section. */
370 static void __attribute__ ((__unused__))
373 asm (INIT_SECTION_ASM_OP);
374 __do_global_ctors_aux ();
375 #ifdef FORCE_INIT_SECTION_ALIGN
376 FORCE_INIT_SECTION_ALIGN;
378 asm (TEXT_SECTION_ASM_OP);
380 /* This is a kludge. The i386 GNU/Linux dynamic linker needs ___brk_addr,
381 __environ and atexit (). We have to make sure they are in the .dynsym
382 section. We accomplish it by making a dummy call here. This
383 code is never reached. */
385 #if defined(__linux__) && defined(__PIC__) && defined(__i386__)
387 extern void *___brk_addr;
388 extern char **__environ;
390 ___brk_addr = __environ;
396 #else /* OBJECT_FORMAT_ELF */
398 /* Stick the real initialization code, followed by a normal sort of
399 function epilogue at the very end of the .init section for this
400 entire root executable file or for this entire shared library file.
402 Note that we use some tricks here to get *just* the body and just
403 a function epilogue (but no function prologue) into the .init
404 section of the crtend.o file. Specifically, we switch to the .text
405 section, start to define a function, and then we switch to the .init
406 section just before the body code.
408 Earlier on, we put the corresponding function prologue into the .init
409 section of the crtbegin.o file (which will be linked in first).
411 Note that we want to invoke all constructors for C++ file-scope static-
412 storage objects AFTER any other possible initialization actions which
413 may be performed by the code in the .init section contributions made by
414 other libraries, etc. That's because those other initializations may
415 include setup operations for very primitive things (e.g. initializing
416 the state of the floating-point coprocessor, etc.) which should be done
417 before we start to execute any of the user's code. */
420 __do_global_ctors_aux (void) /* prologue goes in .text section */
422 asm (INIT_SECTION_ASM_OP);
423 DO_GLOBAL_CTORS_BODY;
424 ON_EXIT (__do_global_dtors, 0);
425 } /* epilogue and body go in .init section */
427 #ifdef FORCE_INIT_SECTION_ALIGN
428 FORCE_INIT_SECTION_ALIGN;
431 asm (TEXT_SECTION_ASM_OP);
433 #endif /* OBJECT_FORMAT_ELF */
435 #else /* defined(INIT_SECTION_ASM_OP) */
437 #ifdef HAS_INIT_SECTION
438 /* This case is used by the Irix 6 port, which supports named sections but
439 not an SVR4-style .init section. __do_global_ctors can be non-static
440 in this case because we protect it with -hidden_symbol. */
441 static func_ptr __CTOR_END__[];
442 #ifdef EH_FRAME_SECTION_ASM_OP
443 extern void __frame_dummy (void);
446 __do_global_ctors (void)
449 #ifdef EH_FRAME_SECTION_ASM_OP
452 for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
457 #endif /* defined(INIT_SECTION_ASM_OP) */
459 /* Force cc1 to switch to .data section. */
460 static func_ptr force_to_data[0] __attribute__ ((__unused__)) = { };
462 /* Put a word containing zero at the end of each of our two lists of function
463 addresses. Note that the words defined here go into the .ctors and .dtors
464 sections of the crtend.o file, and since that file is always linked in
465 last, these words naturally end up at the very ends of the two lists
466 contained in these two sections. */
471 asm (CTORS_SECTION_ASM_OP); /* cc1 doesn't know that we are switching! */
472 STATIC func_ptr __CTOR_END__[1] = { (func_ptr) 0 };
478 asm (DTORS_SECTION_ASM_OP); /* cc1 doesn't know that we are switching! */
479 STATIC func_ptr __DTOR_END__[1] __attribute__ ((__unused__))
483 #ifdef EH_FRAME_SECTION_ASM_OP
484 /* Terminate the frame unwind info section with a 4byte 0 as a sentinel;
485 this would be the 'length' field in a real FDE. */
487 typedef unsigned int ui32 __attribute__ ((mode (SI)));
488 asm (EH_FRAME_SECTION_ASM_OP);
489 STATIC ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
490 #endif /* EH_FRAME_SECTION */
492 #endif /* defined(CRT_END) */
494 #else /* OBJECT_FORMAT_MACHO */
496 /* For Mach-O format executables, we assume that the system's runtime is
497 smart enough to handle constructors and destructors, but doesn't have
498 an init section (if it can't even handle constructors/destructors
499 you should be using INVOKE__main, not crtstuff). All we need to do
500 is install/deinstall the frame information for exceptions. We do this
501 by putting a constructor in crtbegin.o and a destructor in crtend.o.
503 crtend.o also puts in the terminating zero in the frame information
506 /* The crtstuff for other object formats use the symbol __EH_FRAME_BEGIN__
507 to figure out the start of the exception frame, but here we use
508 getsectbynamefromheader to find this value. Either method would work,
509 but this method avoids creating any global symbols, which seems
512 #include <mach-o/ldsyms.h>
513 extern const struct section *
514 getsectbynamefromheader (const struct mach_header *,
515 const char *, const char *);
519 static void __reg_frame_ctor () __attribute__ ((constructor));
522 __reg_frame_ctor (void)
524 static struct object object;
525 const struct section *eh_frame;
527 eh_frame = getsectbynamefromheader (&_mh_execute_header,
528 "__TEXT", "__eh_frame");
529 __register_frame_info ((void *) eh_frame->addr, &object);
532 #endif /* CRT_BEGIN */
536 static void __dereg_frame_dtor () __attribute__ ((destructor));
540 __dereg_frame_dtor (void)
542 const struct section *eh_frame;
544 eh_frame = getsectbynamefromheader (&_mh_execute_header,
545 "__TEXT", "__eh_frame");
546 __deregister_frame_info ((void *) eh_frame->addr);
549 /* Terminate the frame section with a final zero. */
551 /* Force cc1 to switch to .data section. */
552 static void * force_to_data[0] __attribute__ ((__unused__)) = { };
554 typedef unsigned int ui32 __attribute__ ((mode (SI)));
555 asm (EH_FRAME_SECTION_ASM_OP);
556 static ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
560 #endif /* OBJECT_FORMAT_MACHO */