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, 2001 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 In addition to the permissions in the GNU General Public License, the
  15 Free Software Foundation gives you unlimited permission to link the
  16 compiled version of this file into combinations with other programs,
  17 and to distribute those combinations without any restriction coming
  18 from the use of this file.  (The General Public License restrictions
  19 do apply in other respects; for example, they cover modification of
  20 the file, and distribution when not linked into a combine
  21 executable.)
  22
  23 GNU CC is distributed in the hope that it will be useful,
  24 but WITHOUT ANY WARRANTY; without even the implied warranty of
  25 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  26 GNU General Public License for more details.
  27
  28 You should have received a copy of the GNU General Public License
  29 along with GNU CC; see the file COPYING.  If not, write to
  30 the Free Software Foundation, 59 Temple Place - Suite 330,
  31 Boston, MA 02111-1307, USA.  */
  32
  33 /* This file is a bit like libgcc1.c/libgcc2.c in that it is compiled
  34    multiple times and yields multiple .o files.
  35
  36    This file is useful on target machines where the object file format
  37    supports multiple "user-defined" sections (e.g. COFF, ELF, ROSE).  On
  38    such systems, this file allows us to avoid running collect (or any
  39    other such slow and painful kludge).  Additionally, if the target
  40    system supports a .init section, this file allows us to support the
  41    linking of C++ code with a non-C++ main program.
  42
  43    Note that if INIT_SECTION_ASM_OP is defined in the tm.h file, then
  44    this file *will* make use of the .init section.  If that symbol is
  45    not defined however, then the .init section will not be used.
  46
  47    Currently, only ELF and COFF are supported.  It is likely however that
  48    ROSE could also be supported, if someone was willing to do the work to
  49    make whatever (small?) adaptations are needed.  (Some work may be
  50    needed on the ROSE assembler and linker also.)
  51
  52    This file must be compiled with gcc.  */
  53
  54 /* It is incorrect to include config.h here, because this file is being
  55    compiled for the target, and hence definitions concerning only the host
  56    do not apply.  */
  57
  58 #include "auto-host.h"
  59 #include "tm.h"
  60 #include "tsystem.h"
  61 #include "unwind-dw2-fde.h"
  62
  63 #ifndef CRT_CALL_STATIC_FUNCTION
  64 # define CRT_CALL_STATIC_FUNCTION(func) func ()
  65 #endif
  66
  67 /* We do not want to add the weak attribute to the declarations of these
  68    routines in unwind-dw2-fde.h because that will cause the definition of
  69    these symbols to be weak as well.
  70
  71    This exposes a core issue, how to handle creating weak references vs
  72    how to create weak definitions.  Either we have to have the definition
  73    of TARGET_WEAK_ATTRIBUTE be conditional in the shared header files or
  74    have a second declaration if we want a function's references to be weak,
  75    but not its definition.
  76
  77    Making TARGET_WEAK_ATTRIBUTE conditional seems like a good solution until
  78    one thinks about scaling to larger problems -- ie, the condition under
  79    which TARGET_WEAK_ATTRIBUTE is active will eventually get far too
  80    complicated.
  81
  82    So, we take an approach similar to #pragma weak -- we have a second
  83    declaration for functions that we want to have weak references.
  84
  85    Neither way is particularly good.  */
  86
  87 /* References to __register_frame_info and __deregister_frame_info should
  88    be weak in this file if at all possible.  */
  89 extern void __register_frame_info (void *, struct object *)
  90                                   TARGET_ATTRIBUTE_WEAK;
  91
  92 extern void *__deregister_frame_info (void *)
  93                                      TARGET_ATTRIBUTE_WEAK;
  94
  95 #ifndef OBJECT_FORMAT_MACHO
  96
  97 /* Provide default definitions for the pseudo-ops used to switch to the
  98    .ctors and .dtors sections.
  99
 100    Note that we want to give these sections the SHF_WRITE attribute
 101    because these sections will actually contain data (i.e. tables of
 102    addresses of functions in the current root executable or shared library
 103    file) and, in the case of a shared library, the relocatable addresses
 104    will have to be properly resolved/relocated (and then written into) by
 105    the dynamic linker when it actually attaches the given shared library
 106    to the executing process.  (Note that on SVR4, you may wish to use the
 107    `-z text' option to the ELF linker, when building a shared library, as
 108    an additional check that you are doing everything right.  But if you do
 109    use the `-z text' option when building a shared library, you will get
 110    errors unless the .ctors and .dtors sections are marked as writable
 111    via the SHF_WRITE attribute.)
 112
 113    These defaults do not include leading spacing, as they will only be
 114    used in asm:s here.  */
 115
 116 #ifndef CTORS_SECTION_ASM_OP
 117 #define CTORS_SECTION_ASM_OP    ".section\t.ctors,\"aw\""
 118 #endif
 119 #ifndef DTORS_SECTION_ASM_OP
 120 #define DTORS_SECTION_ASM_OP    ".section\t.dtors,\"aw\""
 121 #endif
 122
 123 #ifdef OBJECT_FORMAT_ELF
 124
 125 /*  Declare a pointer to void function type.  */
 126 typedef void (*func_ptr) (void);
 127 #define STATIC static
 128
 129 #else  /* OBJECT_FORMAT_ELF */
 130
 131 #include "gbl-ctors.h"
 132
 133 #define STATIC
 134
 135 #endif /* OBJECT_FORMAT_ELF */
 136
 137 #ifdef CRT_BEGIN
 138
 139 #ifdef INIT_SECTION_ASM_OP
 140
 141 #ifdef OBJECT_FORMAT_ELF
 142
 143 /* Declare the __dso_handle variable.  It should have a unique value
 144    in every shared-object; in a main program its value is zero.  The
 145    object should in any case be protected.  This means the instance
 146    in one DSO or the main program is not used in another object.  The
 147    dynamic linker takes care of this.  */
 148
 149 /* XXX Ideally the following should be implemented using
 150        __attribute__ ((__visibility__ ("hidden")))
 151    but the __attribute__ support is not yet there.  */
 152 #ifdef HAVE_GAS_HIDDEN
 153 asm (".hidden\t__dso_handle");
 154 #endif
 155
 156 #ifdef CRTSTUFFS_O
 157 void *__dso_handle = &__dso_handle;
 158 #else
 159 void *__dso_handle = 0;
 160 #endif
 161
 162 /* The __cxa_finalize function may not be available so we use only a
 163    weak declaration.  */
 164 extern void __cxa_finalize (void *) TARGET_ATTRIBUTE_WEAK;
 165
 166 /* Run all the global destructors on exit from the program.  */
 167
 168 /* Some systems place the number of pointers in the first word of the
 169    table.  On SVR4 however, that word is -1.  In all cases, the table is
 170    null-terminated.  On SVR4, we start from the beginning of the list and
 171    invoke each per-compilation-unit destructor routine in order
 172    until we find that null.
 173
 174    Note that this function MUST be static.  There will be one of these
 175    functions in each root executable and one in each shared library, but
 176    although they all have the same code, each one is unique in that it
 177    refers to one particular associated `__DTOR_LIST__' which belongs to the
 178    same particular root executable or shared library file.
 179
 180    On some systems, this routine is run more than once from the .fini,
 181    when exit is called recursively, so we arrange to remember where in
 182    the list we left off processing, and we resume at that point,
 183    should we be re-invoked.  */
 184
 185 static char __EH_FRAME_BEGIN__[];
 186 static func_ptr __DTOR_LIST__[];
 187 static void
 188 __do_global_dtors_aux (void)
 189 {
 190   static func_ptr *p = __DTOR_LIST__ + 1;
 191   static int completed = 0;
 192
 193   if (completed)
 194     return;
 195
 196 #ifdef CRTSTUFFS_O
 197   if (__cxa_finalize)
 198     __cxa_finalize (__dso_handle);
 199 #endif
 200
 201   while (*p)
 202     {
 203       p++;
 204       (*(p-1)) ();
 205     }
 206
 207 #ifdef EH_FRAME_SECTION_ASM_OP
 208   if (__deregister_frame_info)
 209     __deregister_frame_info (__EH_FRAME_BEGIN__);
 210 #endif
 211   completed = 1;
 212 }
 213
 214
 215 /* Stick a call to __do_global_dtors_aux into the .fini section.  */
 216
 217 static void __attribute__ ((__unused__))
 218 fini_dummy (void)
 219 {
 220   asm (FINI_SECTION_ASM_OP);
 221   CRT_CALL_STATIC_FUNCTION (__do_global_dtors_aux);
 222 #ifdef FORCE_FINI_SECTION_ALIGN
 223   FORCE_FINI_SECTION_ALIGN;
 224 #endif
 225   asm (TEXT_SECTION_ASM_OP);
 226 }
 227
 228 #ifdef EH_FRAME_SECTION_ASM_OP
 229 /* Stick a call to __register_frame_info into the .init section.  For some
 230    reason calls with no arguments work more reliably in .init, so stick the
 231    call in another function.  */
 232
 233 static void
 234 frame_dummy (void)
 235 {
 236   static struct object object;
 237   if (__register_frame_info)
 238     __register_frame_info (__EH_FRAME_BEGIN__, &object);
 239 }
 240
 241 static void __attribute__ ((__unused__))
 242 init_dummy (void)
 243 {
 244   asm (INIT_SECTION_ASM_OP);
 245   CRT_CALL_STATIC_FUNCTION (frame_dummy);
 246 #ifdef FORCE_INIT_SECTION_ALIGN
 247   FORCE_INIT_SECTION_ALIGN;
 248 #endif
 249   asm (TEXT_SECTION_ASM_OP);
 250 }
 251 #endif /* EH_FRAME_SECTION_ASM_OP */
 252
 253 #else  /* OBJECT_FORMAT_ELF */
 254
 255 /* The function __do_global_ctors_aux is compiled twice (once in crtbegin.o
 256    and once in crtend.o).  It must be declared static to avoid a link
 257    error.  Here, we define __do_global_ctors as an externally callable
 258    function.  It is externally callable so that __main can invoke it when
 259    INVOKE__main is defined.  This has the additional effect of forcing cc1
 260    to switch to the .text section.  */
 261
 262 static void __do_global_ctors_aux (void);
 263 void
 264 __do_global_ctors (void)
 265 {
 266 #ifdef INVOKE__main  /* If __main won't actually call __do_global_ctors
 267                         then it doesn't matter what's inside the function.
 268                         The inside of __do_global_ctors_aux is called
 269                         automatically in that case.
 270                         And the Alliant fx2800 linker crashes
 271                         on this reference.  So prevent the crash.  */
 272   __do_global_ctors_aux ();
 273 #endif
 274 }
 275
 276 asm (INIT_SECTION_ASM_OP);      /* cc1 doesn't know that we are switching! */
 277
 278 /* On some svr4 systems, the initial .init section preamble code provided in
 279    crti.o may do something, such as bump the stack, which we have to
 280    undo before we reach the function prologue code for __do_global_ctors
 281    (directly below).  For such systems, define the macro INIT_SECTION_PREAMBLE
 282    to expand into the code needed to undo the actions of the crti.o file.  */
 283
 284 #ifdef INIT_SECTION_PREAMBLE
 285   INIT_SECTION_PREAMBLE;
 286 #endif
 287
 288 /* A routine to invoke all of the global constructors upon entry to the
 289    program.  We put this into the .init section (for systems that have
 290    such a thing) so that we can properly perform the construction of
 291    file-scope static-storage C++ objects within shared libraries.   */
 292
 293 static void
 294 __do_global_ctors_aux (void)    /* prologue goes in .init section */
 295 {
 296 #ifdef FORCE_INIT_SECTION_ALIGN
 297   FORCE_INIT_SECTION_ALIGN;     /* Explicit align before switch to .text */
 298 #endif
 299   asm (TEXT_SECTION_ASM_OP);    /* don't put epilogue and body in .init */
 300   DO_GLOBAL_CTORS_BODY;
 301   atexit (__do_global_dtors);
 302 }
 303
 304 #endif /* OBJECT_FORMAT_ELF */
 305
 306 #else /* defined(INIT_SECTION_ASM_OP) */
 307
 308 #ifdef HAS_INIT_SECTION
 309 /* This case is used by the Irix 6 port, which supports named sections but
 310    not an SVR4-style .fini section.  __do_global_dtors can be non-static
 311    in this case because we protect it with -hidden_symbol.  */
 312
 313 static char __EH_FRAME_BEGIN__[];
 314 static func_ptr __DTOR_LIST__[];
 315 void
 316 __do_global_dtors (void)
 317 {
 318   func_ptr *p;
 319   for (p = __DTOR_LIST__ + 1; *p; p++)
 320     (*p) ();
 321
 322 #ifdef EH_FRAME_SECTION_ASM_OP
 323   if (__deregister_frame_info)
 324     __deregister_frame_info (__EH_FRAME_BEGIN__);
 325 #endif
 326 }
 327
 328 #ifdef EH_FRAME_SECTION_ASM_OP
 329 /* Define a function here to call __register_frame.  crtend.o is linked in
 330    after libgcc.a, and hence can't call libgcc.a functions directly.  That
 331    can lead to unresolved function references.  */
 332 void
 333 __frame_dummy (void)
 334 {
 335   static struct object object;
 336   if (__register_frame_info)
 337     __register_frame_info (__EH_FRAME_BEGIN__, &object);
 338 }
 339 #endif
 340 #endif
 341
 342 #endif /* defined(INIT_SECTION_ASM_OP) */
 343
 344 /* Force cc1 to switch to .data section.  */
 345 static func_ptr force_to_data[1] __attribute__ ((__unused__)) = { };
 346
 347 /* NOTE:  In order to be able to support SVR4 shared libraries, we arrange
 348    to have one set of symbols { __CTOR_LIST__, __DTOR_LIST__, __CTOR_END__,
 349    __DTOR_END__ } per root executable and also one set of these symbols
 350    per shared library.  So in any given whole process image, we may have
 351    multiple definitions of each of these symbols.  In order to prevent
 352    these definitions from conflicting with one another, and in order to
 353    ensure that the proper lists are used for the initialization/finalization
 354    of each individual shared library (respectively), we give these symbols
 355    only internal (i.e. `static') linkage, and we also make it a point to
 356    refer to only the __CTOR_END__ symbol in crtend.o and the __DTOR_LIST__
 357    symbol in crtbegin.o, where they are defined.  */
 358
 359 /* The -1 is a flag to __do_global_[cd]tors
 360    indicating that this table does not start with a count of elements.  */
 361 #ifdef CTOR_LIST_BEGIN
 362 CTOR_LIST_BEGIN;
 363 #else
 364 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 365 STATIC func_ptr __CTOR_LIST__[1] __attribute__ ((__unused__))
 366   = { (func_ptr) (-1) };
 367 #endif
 368
 369 #ifdef DTOR_LIST_BEGIN
 370 DTOR_LIST_BEGIN;
 371 #else
 372 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 373 STATIC func_ptr __DTOR_LIST__[1] = { (func_ptr) (-1) };
 374 #endif
 375
 376 #ifdef EH_FRAME_SECTION_ASM_OP
 377 /* Stick a label at the beginning of the frame unwind info so we can register
 378    and deregister it with the exception handling library code.  */
 379
 380 asm (EH_FRAME_SECTION_ASM_OP);
 381 #ifdef INIT_SECTION_ASM_OP
 382 STATIC
 383 #endif
 384 char __EH_FRAME_BEGIN__[] = { };
 385 #endif /* EH_FRAME_SECTION_ASM_OP */
 386
 387 #endif /* defined(CRT_BEGIN) */
 388
 389 #ifdef CRT_END
 390
 391 #ifdef INIT_SECTION_ASM_OP
 392
 393 #ifdef OBJECT_FORMAT_ELF
 394
 395 static func_ptr __CTOR_END__[];
 396 static void
 397 __do_global_ctors_aux (void)
 398 {
 399   func_ptr *p;
 400   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 401     (*p) ();
 402 }
 403
 404 /* Stick a call to __do_global_ctors_aux into the .init section.  */
 405
 406 static void __attribute__ ((__unused__))
 407 init_dummy (void)
 408 {
 409   asm (INIT_SECTION_ASM_OP);
 410   CRT_CALL_STATIC_FUNCTION (__do_global_ctors_aux);
 411 #ifdef FORCE_INIT_SECTION_ALIGN
 412   FORCE_INIT_SECTION_ALIGN;
 413 #endif
 414   asm (TEXT_SECTION_ASM_OP);
 415 #ifdef CRT_END_INIT_DUMMY
 416   CRT_END_INIT_DUMMY;
 417 #endif
 418 }
 419
 420 #else  /* OBJECT_FORMAT_ELF */
 421
 422 /* Stick the real initialization code, followed by a normal sort of
 423    function epilogue at the very end of the .init section for this
 424    entire root executable file or for this entire shared library file.
 425
 426    Note that we use some tricks here to get *just* the body and just
 427    a function epilogue (but no function prologue) into the .init
 428    section of the crtend.o file.  Specifically, we switch to the .text
 429    section, start to define a function, and then we switch to the .init
 430    section just before the body code.
 431
 432    Earlier on, we put the corresponding function prologue into the .init
 433    section of the crtbegin.o file (which will be linked in first).
 434
 435    Note that we want to invoke all constructors for C++ file-scope static-
 436    storage objects AFTER any other possible initialization actions which
 437    may be performed by the code in the .init section contributions made by
 438    other libraries, etc.  That's because those other initializations may
 439    include setup operations for very primitive things (e.g. initializing
 440    the state of the floating-point coprocessor, etc.) which should be done
 441    before we start to execute any of the user's code.  */
 442
 443 static void
 444 __do_global_ctors_aux (void)    /* prologue goes in .text section */
 445 {
 446   asm (INIT_SECTION_ASM_OP);
 447   DO_GLOBAL_CTORS_BODY;
 448   atexit (__do_global_dtors);
 449 }                               /* epilogue and body go in .init section */
 450
 451 #ifdef FORCE_INIT_SECTION_ALIGN
 452 FORCE_INIT_SECTION_ALIGN;
 453 #endif
 454
 455 asm (TEXT_SECTION_ASM_OP);
 456
 457 #endif /* OBJECT_FORMAT_ELF */
 458
 459 #else /* defined(INIT_SECTION_ASM_OP) */
 460
 461 #ifdef HAS_INIT_SECTION
 462 /* This case is used by the Irix 6 port, which supports named sections but
 463    not an SVR4-style .init section.  __do_global_ctors can be non-static
 464    in this case because we protect it with -hidden_symbol.  */
 465 static func_ptr __CTOR_END__[];
 466 #ifdef EH_FRAME_SECTION_ASM_OP
 467 extern void __frame_dummy (void);
 468 #endif
 469 void
 470 __do_global_ctors (void)
 471 {
 472   func_ptr *p;
 473 #ifdef EH_FRAME_SECTION_ASM_OP
 474   __frame_dummy ();
 475 #endif
 476   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 477     (*p) ();
 478 }
 479 #endif
 480
 481 #endif /* defined(INIT_SECTION_ASM_OP) */
 482
 483 /* Force cc1 to switch to .data section.  */
 484 static func_ptr force_to_data[1] __attribute__ ((__unused__)) = { };
 485
 486 /* Put a word containing zero at the end of each of our two lists of function
 487    addresses.  Note that the words defined here go into the .ctors and .dtors
 488    sections of the crtend.o file, and since that file is always linked in
 489    last, these words naturally end up at the very ends of the two lists
 490    contained in these two sections.  */
 491
 492 #ifdef CTOR_LIST_END
 493 CTOR_LIST_END;
 494 #else
 495 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 496 STATIC func_ptr __CTOR_END__[1] = { (func_ptr) 0 };
 497 #endif
 498
 499 #ifdef DTOR_LIST_END
 500 DTOR_LIST_END;
 501 #else
 502 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 503 STATIC func_ptr __DTOR_END__[1] __attribute__ ((__unused__))
 504   = { (func_ptr) 0 };
 505 #endif
 506
 507 #ifdef EH_FRAME_SECTION_ASM_OP
 508 /* Terminate the frame unwind info section with a 4byte 0 as a sentinel;
 509    this would be the 'length' field in a real FDE.  */
 510
 511 typedef unsigned int ui32 __attribute__ ((mode (SI)));
 512 asm (EH_FRAME_SECTION_ASM_OP);
 513 STATIC ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
 514 #endif /* EH_FRAME_SECTION */
 515
 516 #endif /* defined(CRT_END) */
 517
 518 #else  /* OBJECT_FORMAT_MACHO */
 519
 520 /* For Mach-O format executables, we assume that the system's runtime is
 521    smart enough to handle constructors and destructors, but doesn't have
 522    an init section (if it can't even handle constructors/destructors
 523    you should be using INVOKE__main, not crtstuff). All we need to do
 524    is install/deinstall the frame information for exceptions. We do this
 525    by putting a constructor in crtbegin.o and a destructor in crtend.o.
 526
 527    crtend.o also puts in the terminating zero in the frame information
 528    segment. */
 529
 530 /* The crtstuff for other object formats use the symbol __EH_FRAME_BEGIN__
 531    to figure out the start of the exception frame, but here we use
 532    getsectbynamefromheader to find this value. Either method would work,
 533    but this method avoids creating any global symbols, which seems
 534    cleaner. */
 535
 536 #include <mach-o/ldsyms.h>
 537 extern const struct section *
 538   getsectbynamefromheader (const struct mach_header *,
 539                            const char *, const char *);
 540
 541 #ifdef CRT_BEGIN
 542
 543 static void __reg_frame_ctor (void) __attribute__ ((constructor));
 544
 545 static void
 546 __reg_frame_ctor (void)
 547 {
 548   static struct object object;
 549   const struct section *eh_frame;
 550
 551   eh_frame = getsectbynamefromheader (&_mh_execute_header,
 552                                       "__TEXT", "__eh_frame");
 553   __register_frame_info ((void *) eh_frame->addr, &object);
 554 }
 555
 556 #endif /* CRT_BEGIN */
 557
 558 #ifdef CRT_END
 559
 560 static void __dereg_frame_dtor (void) __attribute__ ((destructor));
 561
 562 static void
 563 __dereg_frame_dtor (void)
 564 {
 565   const struct section *eh_frame;
 566
 567   eh_frame = getsectbynamefromheader (&_mh_execute_header,
 568                                       "__TEXT", "__eh_frame");
 569   __deregister_frame_info ((void *) eh_frame->addr);
 570 }
 571
 572 /* Terminate the frame section with a final zero. */
 573
 574 /* Force cc1 to switch to .data section.  */
 575 static void * force_to_data[1] __attribute__ ((__unused__)) = { };
 576
 577 typedef unsigned int ui32 __attribute__ ((mode (SI)));
 578 asm (EH_FRAME_SECTION_ASM_OP);
 579 static ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
 580
 581 #endif /* CRT_END */
 582
 583 #endif /* OBJECT_FORMAT_MACHO */
 584