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