gcc/crtstuff.c

   1 /* Specialized bits of code needed to support construction and
   2    destruction of file-scope objects in C++ code.
   3    Copyright (C) 1991, 1994, 1995, 1996, 1997, 1998,
   4    1999, 2000 Free Software Foundation, Inc.
   5    Contributed by Ron Guilmette (rfg@monkeys.com).
   6
   7 This file is part of GNU CC.
   8
   9 GNU CC is free software; you can redistribute it and/or modify
  10 it under the terms of the GNU General Public License as published by
  11 the Free Software Foundation; either version 2, or (at your option)
  12 any later version.
  13
  14 GNU CC is distributed in the hope that it will be useful,
  15 but WITHOUT ANY WARRANTY; without even the implied warranty of
  16 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17 GNU General Public License for more details.
  18
  19 You should have received a copy of the GNU General Public License
  20 along with GNU CC; see the file COPYING.  If not, write to
  21 the Free Software Foundation, 59 Temple Place - Suite 330,
  22 Boston, MA 02111-1307, USA.  */
  23
  24 /* As a special exception, if you link this library with files
  25    compiled with GCC to produce an executable, this does not cause
  26    the resulting executable to be covered by the GNU General Public License.
  27    This exception does not however invalidate any other reasons why
  28    the executable file might be covered by the GNU General Public License.  */
  29
  30 /* This file is a bit like libgcc1.c/libgcc2.c in that it is compiled
  31    multiple times and yields multiple .o files.
  32
  33    This file is useful on target machines where the object file format
  34    supports multiple "user-defined" sections (e.g. COFF, ELF, ROSE).  On
  35    such systems, this file allows us to avoid running collect (or any
  36    other such slow and painful kludge).  Additionally, if the target
  37    system supports a .init section, this file allows us to support the
  38    linking of C++ code with a non-C++ main program.
  39
  40    Note that if INIT_SECTION_ASM_OP is defined in the tm.h file, then
  41    this file *will* make use of the .init section.  If that symbol is
  42    not defined however, then the .init section will not be used.
  43
  44    Currently, only ELF and COFF are supported.  It is likely however that
  45    ROSE could also be supported, if someone was willing to do the work to
  46    make whatever (small?) adaptations are needed.  (Some work may be
  47    needed on the ROSE assembler and linker also.)
  48
  49    This file must be compiled with gcc.  */
  50
  51 /* It is incorrect to include config.h here, because this file is being
  52    compiled for the target, and hence definitions concerning only the host
  53    do not apply.  */
  54
  55 #include "tm.h"
  56 #include "tsystem.h"
  57
  58 #include "defaults.h"
  59 #include "frame.h"
  60
  61 /* We do not want to add the weak attribute to the declarations of these
  62    routines in frame.h because that will cause the definition of these
  63    symbols to be weak as well.
  64
  65    This exposes a core issue, how to handle creating weak references vs
  66    how to create weak definitions.  Either we have to have the definition
  67    of TARGET_WEAK_ATTRIBUTE be conditional in the shared header files or
  68    have a second declaration if we want a function's references to be weak,
  69    but not its definition.
  70
  71    Making TARGET_WEAK_ATTRIBUTE conditional seems like a good solution until
  72    one thinks about scaling to larger problems -- ie, the condition under
  73    which TARGET_WEAK_ATTRIBUTE is active will eventually get far too
  74    complicated.
  75
  76    So, we take an approach similar to #pragma weak -- we have a second
  77    declaration for functions that we want to have weak references.
  78
  79    Neither way is particularly good.  */
  80
  81 /* References to __register_frame_info and __deregister_frame_info should
  82    be weak in this file if at all possible.  */
  83 extern void __register_frame_info (void *, struct object *)
  84                                   TARGET_ATTRIBUTE_WEAK;
  85
  86 extern void *__deregister_frame_info (void *)
  87                                      TARGET_ATTRIBUTE_WEAK;
  88
  89 #ifndef OBJECT_FORMAT_MACHO
  90
  91 /* Provide default definitions for the pseudo-ops used to switch to the
  92    .ctors and .dtors sections.
  93
  94    Note that we want to give these sections the SHF_WRITE attribute
  95    because these sections will actually contain data (i.e. tables of
  96    addresses of functions in the current root executable or shared library
  97    file) and, in the case of a shared library, the relocatable addresses
  98    will have to be properly resolved/relocated (and then written into) by
  99    the dynamic linker when it actually attaches the given shared library
 100    to the executing process.  (Note that on SVR4, you may wish to use the
 101    `-z text' option to the ELF linker, when building a shared library, as
 102    an additional check that you are doing everything right.  But if you do
 103    use the `-z text' option when building a shared library, you will get
 104    errors unless the .ctors and .dtors sections are marked as writable
 105    via the SHF_WRITE attribute.)  */
 106
 107 #ifndef CTORS_SECTION_ASM_OP
 108 #define CTORS_SECTION_ASM_OP    ".section\t.ctors,\"aw\""
 109 #endif
 110 #ifndef DTORS_SECTION_ASM_OP
 111 #define DTORS_SECTION_ASM_OP    ".section\t.dtors,\"aw\""
 112 #endif
 113
 114 #ifdef OBJECT_FORMAT_ELF
 115
 116 /*  Declare a pointer to void function type.  */
 117 typedef void (*func_ptr) (void);
 118 #define STATIC static
 119
 120 #else  /* OBJECT_FORMAT_ELF */
 121
 122 #include "gbl-ctors.h"
 123
 124 #define STATIC
 125
 126 #endif /* OBJECT_FORMAT_ELF */
 127
 128 #ifdef CRT_BEGIN
 129
 130 #ifdef INIT_SECTION_ASM_OP
 131
 132 #ifdef OBJECT_FORMAT_ELF
 133
 134 /* Declare the __dso_handle variable.  It should have a unique value
 135    in every shared-object; in a main program its value is zero.  */
 136
 137 #ifdef CRTSTUFFS_O
 138 void *__dso_handle = &__dso_handle;
 139 #else
 140 void *__dso_handle = 0;
 141 #endif
 142
 143 /* The __cxa_finalize function may not be available so we use only a
 144    weak declaration.  */
 145 extern void __cxa_finalize (void *) TARGET_ATTRIBUTE_WEAK;
 146
 147 /* Run all the global destructors on exit from the program.  */
 148
 149 /* Some systems place the number of pointers in the first word of the
 150    table.  On SVR4 however, that word is -1.  In all cases, the table is
 151    null-terminated.  On SVR4, we start from the beginning of the list and
 152    invoke each per-compilation-unit destructor routine in order
 153    until we find that null.
 154
 155    Note that this function MUST be static.  There will be one of these
 156    functions in each root executable and one in each shared library, but
 157    although they all have the same code, each one is unique in that it
 158    refers to one particular associated `__DTOR_LIST__' which belongs to the
 159    same particular root executable or shared library file.
 160
 161    On some systems, this routine is run more than once from the .fini,
 162    when exit is called recursively, so we arrange to remember where in
 163    the list we left off processing, and we resume at that point,
 164    should we be re-invoked.  */
 165
 166 static char __EH_FRAME_BEGIN__[];
 167 static func_ptr __DTOR_LIST__[];
 168 static void
 169 __do_global_dtors_aux (void)
 170 {
 171   static func_ptr *p = __DTOR_LIST__ + 1;
 172   static int completed = 0;
 173
 174   if (completed)
 175     return;
 176
 177 #ifdef CRTSTUFFS_O
 178   if (__cxa_finalize)
 179     __cxa_finalize (__dso_handle);
 180 #endif
 181
 182   while (*p)
 183     {
 184       p++;
 185       (*(p-1)) ();
 186     }
 187
 188 #ifdef EH_FRAME_SECTION_ASM_OP
 189   if (__deregister_frame_info)
 190     __deregister_frame_info (__EH_FRAME_BEGIN__);
 191 #endif
 192   completed = 1;
 193 }
 194
 195
 196 /* Stick a call to __do_global_dtors_aux into the .fini section.  */
 197
 198 static void __attribute__ ((__unused__))
 199 fini_dummy (void)
 200 {
 201   asm (FINI_SECTION_ASM_OP);
 202   __do_global_dtors_aux ();
 203 #ifdef FORCE_FINI_SECTION_ALIGN
 204   FORCE_FINI_SECTION_ALIGN;
 205 #endif
 206   asm (TEXT_SECTION_ASM_OP);
 207 }
 208
 209 #ifdef EH_FRAME_SECTION_ASM_OP
 210 /* Stick a call to __register_frame_info into the .init section.  For some
 211    reason calls with no arguments work more reliably in .init, so stick the
 212    call in another function.  */
 213
 214 static void
 215 frame_dummy (void)
 216 {
 217   static struct object object;
 218   if (__register_frame_info)
 219     __register_frame_info (__EH_FRAME_BEGIN__, &object);
 220 }
 221
 222 static void __attribute__ ((__unused__))
 223 init_dummy (void)
 224 {
 225   asm (INIT_SECTION_ASM_OP);
 226   frame_dummy ();
 227 #ifdef FORCE_INIT_SECTION_ALIGN
 228   FORCE_INIT_SECTION_ALIGN;
 229 #endif
 230   asm (TEXT_SECTION_ASM_OP);
 231 }
 232 #endif /* EH_FRAME_SECTION_ASM_OP */
 233
 234 #else  /* OBJECT_FORMAT_ELF */
 235
 236 /* The function __do_global_ctors_aux is compiled twice (once in crtbegin.o
 237    and once in crtend.o).  It must be declared static to avoid a link
 238    error.  Here, we define __do_global_ctors as an externally callable
 239    function.  It is externally callable so that __main can invoke it when
 240    INVOKE__main is defined.  This has the additional effect of forcing cc1
 241    to switch to the .text section.  */
 242
 243 static void __do_global_ctors_aux (void);
 244 void
 245 __do_global_ctors (void)
 246 {
 247 #ifdef INVOKE__main  /* If __main won't actually call __do_global_ctors
 248                         then it doesn't matter what's inside the function.
 249                         The inside of __do_global_ctors_aux is called
 250                         automatically in that case.
 251                         And the Alliant fx2800 linker crashes
 252                         on this reference.  So prevent the crash.  */
 253   __do_global_ctors_aux ();
 254 #endif
 255 }
 256
 257 asm (INIT_SECTION_ASM_OP);      /* cc1 doesn't know that we are switching! */
 258
 259 /* On some svr4 systems, the initial .init section preamble code provided in
 260    crti.o may do something, such as bump the stack, which we have to
 261    undo before we reach the function prologue code for __do_global_ctors
 262    (directly below).  For such systems, define the macro INIT_SECTION_PREAMBLE
 263    to expand into the code needed to undo the actions of the crti.o file.  */
 264
 265 #ifdef INIT_SECTION_PREAMBLE
 266   INIT_SECTION_PREAMBLE;
 267 #endif
 268
 269 /* A routine to invoke all of the global constructors upon entry to the
 270    program.  We put this into the .init section (for systems that have
 271    such a thing) so that we can properly perform the construction of
 272    file-scope static-storage C++ objects within shared libraries.   */
 273
 274 static void
 275 __do_global_ctors_aux (void)    /* prologue goes in .init section */
 276 {
 277 #ifdef FORCE_INIT_SECTION_ALIGN
 278   FORCE_INIT_SECTION_ALIGN;     /* Explicit align before switch to .text */
 279 #endif
 280   asm (TEXT_SECTION_ASM_OP);    /* don't put epilogue and body in .init */
 281   DO_GLOBAL_CTORS_BODY;
 282   atexit (__do_global_dtors);
 283 }
 284
 285 #endif /* OBJECT_FORMAT_ELF */
 286
 287 #else /* defined(INIT_SECTION_ASM_OP) */
 288
 289 #ifdef HAS_INIT_SECTION
 290 /* This case is used by the Irix 6 port, which supports named sections but
 291    not an SVR4-style .fini section.  __do_global_dtors can be non-static
 292    in this case because we protect it with -hidden_symbol.  */
 293
 294 static char __EH_FRAME_BEGIN__[];
 295 static func_ptr __DTOR_LIST__[];
 296 void
 297 __do_global_dtors (void)
 298 {
 299   func_ptr *p;
 300   for (p = __DTOR_LIST__ + 1; *p; p++)
 301     (*p) ();
 302
 303 #ifdef EH_FRAME_SECTION_ASM_OP
 304   if (__deregister_frame_info)
 305     __deregister_frame_info (__EH_FRAME_BEGIN__);
 306 #endif
 307 }
 308
 309 #ifdef EH_FRAME_SECTION_ASM_OP
 310 /* Define a function here to call __register_frame.  crtend.o is linked in
 311    after libgcc.a, and hence can't call libgcc.a functions directly.  That
 312    can lead to unresolved function references.  */
 313 void
 314 __frame_dummy (void)
 315 {
 316   static struct object object;
 317   if (__register_frame_info)
 318     __register_frame_info (__EH_FRAME_BEGIN__, &object);
 319 }
 320 #endif
 321 #endif
 322
 323 #endif /* defined(INIT_SECTION_ASM_OP) */
 324
 325 /* Force cc1 to switch to .data section.  */
 326 static func_ptr force_to_data[0] __attribute__ ((__unused__)) = { };
 327
 328 /* NOTE:  In order to be able to support SVR4 shared libraries, we arrange
 329    to have one set of symbols { __CTOR_LIST__, __DTOR_LIST__, __CTOR_END__,
 330    __DTOR_END__ } per root executable and also one set of these symbols
 331    per shared library.  So in any given whole process image, we may have
 332    multiple definitions of each of these symbols.  In order to prevent
 333    these definitions from conflicting with one another, and in order to
 334    ensure that the proper lists are used for the initialization/finalization
 335    of each individual shared library (respectively), we give these symbols
 336    only internal (i.e. `static') linkage, and we also make it a point to
 337    refer to only the __CTOR_END__ symbol in crtend.o and the __DTOR_LIST__
 338    symbol in crtbegin.o, where they are defined.  */
 339
 340 /* The -1 is a flag to __do_global_[cd]tors
 341    indicating that this table does not start with a count of elements.  */
 342 #ifdef CTOR_LIST_BEGIN
 343 CTOR_LIST_BEGIN;
 344 #else
 345 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 346 STATIC func_ptr __CTOR_LIST__[1] __attribute__ ((__unused__))
 347   = { (func_ptr) (-1) };
 348 #endif
 349
 350 #ifdef DTOR_LIST_BEGIN
 351 DTOR_LIST_BEGIN;
 352 #else
 353 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 354 STATIC func_ptr __DTOR_LIST__[1] = { (func_ptr) (-1) };
 355 #endif
 356
 357 #ifdef EH_FRAME_SECTION_ASM_OP
 358 /* Stick a label at the beginning of the frame unwind info so we can register
 359    and deregister it with the exception handling library code.  */
 360
 361 asm (EH_FRAME_SECTION_ASM_OP);
 362 #ifdef INIT_SECTION_ASM_OP
 363 STATIC
 364 #endif
 365 char __EH_FRAME_BEGIN__[] = { };
 366 #endif /* EH_FRAME_SECTION_ASM_OP */
 367
 368 #endif /* defined(CRT_BEGIN) */
 369
 370 #ifdef CRT_END
 371
 372 #ifdef INIT_SECTION_ASM_OP
 373
 374 #ifdef OBJECT_FORMAT_ELF
 375
 376 static func_ptr __CTOR_END__[];
 377 static void
 378 __do_global_ctors_aux (void)
 379 {
 380   func_ptr *p;
 381   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 382     (*p) ();
 383 }
 384
 385 /* Stick a call to __do_global_ctors_aux into the .init section.  */
 386
 387 static void __attribute__ ((__unused__))
 388 init_dummy (void)
 389 {
 390   asm (INIT_SECTION_ASM_OP);
 391   __do_global_ctors_aux ();
 392 #ifdef FORCE_INIT_SECTION_ALIGN
 393   FORCE_INIT_SECTION_ALIGN;
 394 #endif
 395   asm (TEXT_SECTION_ASM_OP);
 396
 397 /* This is a kludge. The i386 GNU/Linux dynamic linker needs ___brk_addr,
 398    __environ and atexit (). We have to make sure they are in the .dynsym
 399    section. We accomplish it by making a dummy call here. This
 400    code is never reached.  */
 401
 402 #if defined(__linux__) && defined(__PIC__) && defined(__i386__)
 403   {
 404     extern void *___brk_addr;
 405     extern char **__environ;
 406
 407     ___brk_addr = __environ;
 408     atexit (0);
 409   }
 410 #endif
 411 }
 412
 413 #else  /* OBJECT_FORMAT_ELF */
 414
 415 /* Stick the real initialization code, followed by a normal sort of
 416    function epilogue at the very end of the .init section for this
 417    entire root executable file or for this entire shared library file.
 418
 419    Note that we use some tricks here to get *just* the body and just
 420    a function epilogue (but no function prologue) into the .init
 421    section of the crtend.o file.  Specifically, we switch to the .text
 422    section, start to define a function, and then we switch to the .init
 423    section just before the body code.
 424
 425    Earlier on, we put the corresponding function prologue into the .init
 426    section of the crtbegin.o file (which will be linked in first).
 427
 428    Note that we want to invoke all constructors for C++ file-scope static-
 429    storage objects AFTER any other possible initialization actions which
 430    may be performed by the code in the .init section contributions made by
 431    other libraries, etc.  That's because those other initializations may
 432    include setup operations for very primitive things (e.g. initializing
 433    the state of the floating-point coprocessor, etc.) which should be done
 434    before we start to execute any of the user's code.  */
 435
 436 static void
 437 __do_global_ctors_aux (void)    /* prologue goes in .text section */
 438 {
 439   asm (INIT_SECTION_ASM_OP);
 440   DO_GLOBAL_CTORS_BODY;
 441   atexit (__do_global_dtors);
 442 }                               /* epilogue and body go in .init section */
 443
 444 #ifdef FORCE_INIT_SECTION_ALIGN
 445 FORCE_INIT_SECTION_ALIGN;
 446 #endif
 447
 448 asm (TEXT_SECTION_ASM_OP);
 449
 450 #endif /* OBJECT_FORMAT_ELF */
 451
 452 #else /* defined(INIT_SECTION_ASM_OP) */
 453
 454 #ifdef HAS_INIT_SECTION
 455 /* This case is used by the Irix 6 port, which supports named sections but
 456    not an SVR4-style .init section.  __do_global_ctors can be non-static
 457    in this case because we protect it with -hidden_symbol.  */
 458 static func_ptr __CTOR_END__[];
 459 #ifdef EH_FRAME_SECTION_ASM_OP
 460 extern void __frame_dummy (void);
 461 #endif
 462 void
 463 __do_global_ctors (void)
 464 {
 465   func_ptr *p;
 466 #ifdef EH_FRAME_SECTION_ASM_OP
 467   __frame_dummy ();
 468 #endif
 469   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 470     (*p) ();
 471 }
 472 #endif
 473
 474 #endif /* defined(INIT_SECTION_ASM_OP) */
 475
 476 /* Force cc1 to switch to .data section.  */
 477 static func_ptr force_to_data[0] __attribute__ ((__unused__)) = { };
 478
 479 /* Put a word containing zero at the end of each of our two lists of function
 480    addresses.  Note that the words defined here go into the .ctors and .dtors
 481    sections of the crtend.o file, and since that file is always linked in
 482    last, these words naturally end up at the very ends of the two lists
 483    contained in these two sections.  */
 484
 485 #ifdef CTOR_LIST_END
 486 CTOR_LIST_END;
 487 #else
 488 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 489 STATIC func_ptr __CTOR_END__[1] = { (func_ptr) 0 };
 490 #endif
 491
 492 #ifdef DTOR_LIST_END
 493 DTOR_LIST_END;
 494 #else
 495 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 496 STATIC func_ptr __DTOR_END__[1] __attribute__ ((__unused__))
 497   = { (func_ptr) 0 };
 498 #endif
 499
 500 #ifdef EH_FRAME_SECTION_ASM_OP
 501 /* Terminate the frame unwind info section with a 4byte 0 as a sentinel;
 502    this would be the 'length' field in a real FDE.  */
 503
 504 typedef unsigned int ui32 __attribute__ ((mode (SI)));
 505 asm (EH_FRAME_SECTION_ASM_OP);
 506 STATIC ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
 507 #endif /* EH_FRAME_SECTION */
 508
 509 #endif /* defined(CRT_END) */
 510
 511 #else  /* OBJECT_FORMAT_MACHO */
 512
 513 /* For Mach-O format executables, we assume that the system's runtime is
 514    smart enough to handle constructors and destructors, but doesn't have
 515    an init section (if it can't even handle constructors/destructors
 516    you should be using INVOKE__main, not crtstuff). All we need to do
 517    is install/deinstall the frame information for exceptions. We do this
 518    by putting a constructor in crtbegin.o and a destructor in crtend.o.
 519
 520    crtend.o also puts in the terminating zero in the frame information
 521    segment. */
 522
 523 /* The crtstuff for other object formats use the symbol __EH_FRAME_BEGIN__
 524    to figure out the start of the exception frame, but here we use
 525    getsectbynamefromheader to find this value. Either method would work,
 526    but this method avoids creating any global symbols, which seems
 527    cleaner. */
 528
 529 #include <mach-o/ldsyms.h>
 530 extern const struct section *
 531   getsectbynamefromheader (const struct mach_header *,
 532                            const char *, const char *);
 533
 534 #ifdef CRT_BEGIN
 535
 536 static void __reg_frame_ctor (void) __attribute__ ((constructor));
 537
 538 static void
 539 __reg_frame_ctor (void)
 540 {
 541   static struct object object;
 542   const struct section *eh_frame;
 543
 544   eh_frame = getsectbynamefromheader (&_mh_execute_header,
 545                                       "__TEXT", "__eh_frame");
 546   __register_frame_info ((void *) eh_frame->addr, &object);
 547 }
 548
 549 #endif /* CRT_BEGIN */
 550
 551 #ifdef CRT_END
 552
 553 static void __dereg_frame_dtor (void) __attribute__ ((destructor));
 554
 555 static void
 556 __dereg_frame_dtor (void)
 557 {
 558   const struct section *eh_frame;
 559
 560   eh_frame = getsectbynamefromheader (&_mh_execute_header,
 561                                       "__TEXT", "__eh_frame");
 562   __deregister_frame_info ((void *) eh_frame->addr);
 563 }
 564
 565 /* Terminate the frame section with a final zero. */
 566
 567 /* Force cc1 to switch to .data section.  */
 568 static void * force_to_data[0] __attribute__ ((__unused__)) = { };
 569
 570 typedef unsigned int ui32 __attribute__ ((mode (SI)));
 571 asm (EH_FRAME_SECTION_ASM_OP);
 572 static ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
 573
 574 #endif /* CRT_END */
 575
 576 #endif /* OBJECT_FORMAT_MACHO */
 577