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 /* We include auto-host.h here to get HAVE_GAS_HIDDEN.  This is
  59    supposedly valid even though this is a "target" file.  */
  60 #include "auto-host.h"
  61 #include "tconfig.h"
  62 #include "tsystem.h"
  63 #include "unwind-dw2-fde.h"
  64
  65 #ifndef CRT_CALL_STATIC_FUNCTION
  66 # define CRT_CALL_STATIC_FUNCTION(func) func ()
  67 #endif
  68
  69 /* We do not want to add the weak attribute to the declarations of these
  70    routines in unwind-dw2-fde.h because that will cause the definition of
  71    these symbols to be weak as well.
  72
  73    This exposes a core issue, how to handle creating weak references vs
  74    how to create weak definitions.  Either we have to have the definition
  75    of TARGET_WEAK_ATTRIBUTE be conditional in the shared header files or
  76    have a second declaration if we want a function's references to be weak,
  77    but not its definition.
  78
  79    Making TARGET_WEAK_ATTRIBUTE conditional seems like a good solution until
  80    one thinks about scaling to larger problems -- ie, the condition under
  81    which TARGET_WEAK_ATTRIBUTE is active will eventually get far too
  82    complicated.
  83
  84    So, we take an approach similar to #pragma weak -- we have a second
  85    declaration for functions that we want to have weak references.
  86
  87    Neither way is particularly good.  */
  88
  89 /* References to __register_frame_info and __deregister_frame_info should
  90    be weak in this file if at all possible.  */
  91 extern void __register_frame_info (void *, struct object *)
  92                                   TARGET_ATTRIBUTE_WEAK;
  93
  94 extern void *__deregister_frame_info (void *)
  95                                      TARGET_ATTRIBUTE_WEAK;
  96
  97 #ifndef OBJECT_FORMAT_MACHO
  98
  99 /* Provide default definitions for the pseudo-ops used to switch to the
 100    .ctors and .dtors sections.
 101
 102    Note that we want to give these sections the SHF_WRITE attribute
 103    because these sections will actually contain data (i.e. tables of
 104    addresses of functions in the current root executable or shared library
 105    file) and, in the case of a shared library, the relocatable addresses
 106    will have to be properly resolved/relocated (and then written into) by
 107    the dynamic linker when it actually attaches the given shared library
 108    to the executing process.  (Note that on SVR4, you may wish to use the
 109    `-z text' option to the ELF linker, when building a shared library, as
 110    an additional check that you are doing everything right.  But if you do
 111    use the `-z text' option when building a shared library, you will get
 112    errors unless the .ctors and .dtors sections are marked as writable
 113    via the SHF_WRITE attribute.)
 114
 115    These defaults do not include leading spacing, as they will only be
 116    used in asm:s here.  */
 117
 118 #ifndef CTORS_SECTION_ASM_OP
 119 #define CTORS_SECTION_ASM_OP    ".section\t.ctors,\"aw\""
 120 #endif
 121 #ifndef DTORS_SECTION_ASM_OP
 122 #define DTORS_SECTION_ASM_OP    ".section\t.dtors,\"aw\""
 123 #endif
 124
 125 #ifdef OBJECT_FORMAT_ELF
 126
 127 /*  Declare a pointer to void function type.  */
 128 typedef void (*func_ptr) (void);
 129 #define STATIC static
 130
 131 #else  /* OBJECT_FORMAT_ELF */
 132
 133 #include "gbl-ctors.h"
 134
 135 #define STATIC
 136
 137 #endif /* OBJECT_FORMAT_ELF */
 138
 139 #ifdef CRT_BEGIN
 140
 141 #ifdef INIT_SECTION_ASM_OP
 142
 143 #ifdef OBJECT_FORMAT_ELF
 144
 145 /* Declare the __dso_handle variable.  It should have a unique value
 146    in every shared-object; in a main program its value is zero.  The
 147    object should in any case be protected.  This means the instance
 148    in one DSO or the main program is not used in another object.  The
 149    dynamic linker takes care of this.  */
 150
 151 /* XXX Ideally the following should be implemented using
 152        __attribute__ ((__visibility__ ("hidden")))
 153    but the __attribute__ support is not yet there.  */
 154 #ifdef HAVE_GAS_HIDDEN
 155 asm (".hidden\t__dso_handle");
 156 #endif
 157
 158 #ifdef CRTSTUFFS_O
 159 void *__dso_handle = &__dso_handle;
 160 #else
 161 void *__dso_handle = 0;
 162 #endif
 163
 164 /* The __cxa_finalize function may not be available so we use only a
 165    weak declaration.  */
 166 extern void __cxa_finalize (void *) TARGET_ATTRIBUTE_WEAK;
 167
 168 /* Run all the global destructors on exit from the program.  */
 169
 170 /* Some systems place the number of pointers in the first word of the
 171    table.  On SVR4 however, that word is -1.  In all cases, the table is
 172    null-terminated.  On SVR4, we start from the beginning of the list and
 173    invoke each per-compilation-unit destructor routine in order
 174    until we find that null.
 175
 176    Note that this function MUST be static.  There will be one of these
 177    functions in each root executable and one in each shared library, but
 178    although they all have the same code, each one is unique in that it
 179    refers to one particular associated `__DTOR_LIST__' which belongs to the
 180    same particular root executable or shared library file.
 181
 182    On some systems, this routine is run more than once from the .fini,
 183    when exit is called recursively, so we arrange to remember where in
 184    the list we left off processing, and we resume at that point,
 185    should we be re-invoked.  */
 186
 187 static char __EH_FRAME_BEGIN__[];
 188 static func_ptr __DTOR_LIST__[];
 189 static void
 190 __do_global_dtors_aux (void)
 191 {
 192   static func_ptr *p = __DTOR_LIST__ + 1;
 193   static int completed = 0;
 194
 195   if (completed)
 196     return;
 197
 198 #ifdef CRTSTUFFS_O
 199   if (__cxa_finalize)
 200     __cxa_finalize (__dso_handle);
 201 #endif
 202
 203   while (*p)
 204     {
 205       p++;
 206       (*(p-1)) ();
 207     }
 208
 209 #ifdef EH_FRAME_SECTION_ASM_OP
 210   if (__deregister_frame_info)
 211     __deregister_frame_info (__EH_FRAME_BEGIN__);
 212 #endif
 213   completed = 1;
 214 }
 215
 216
 217 /* Stick a call to __do_global_dtors_aux into the .fini section.  */
 218
 219 static void __attribute__ ((__unused__))
 220 fini_dummy (void)
 221 {
 222   asm (FINI_SECTION_ASM_OP);
 223   CRT_CALL_STATIC_FUNCTION (__do_global_dtors_aux);
 224 #ifdef FORCE_FINI_SECTION_ALIGN
 225   FORCE_FINI_SECTION_ALIGN;
 226 #endif
 227   asm (TEXT_SECTION_ASM_OP);
 228 }
 229
 230 #ifdef EH_FRAME_SECTION_ASM_OP
 231 /* Stick a call to __register_frame_info into the .init section.  For some
 232    reason calls with no arguments work more reliably in .init, so stick the
 233    call in another function.  */
 234
 235 static void
 236 frame_dummy (void)
 237 {
 238   static struct object object;
 239   if (__register_frame_info)
 240     __register_frame_info (__EH_FRAME_BEGIN__, &object);
 241 }
 242
 243 static void __attribute__ ((__unused__))
 244 init_dummy (void)
 245 {
 246   asm (INIT_SECTION_ASM_OP);
 247   CRT_CALL_STATIC_FUNCTION (frame_dummy);
 248 #ifdef FORCE_INIT_SECTION_ALIGN
 249   FORCE_INIT_SECTION_ALIGN;
 250 #endif
 251   asm (TEXT_SECTION_ASM_OP);
 252 }
 253 #endif /* EH_FRAME_SECTION_ASM_OP */
 254
 255 #else  /* OBJECT_FORMAT_ELF */
 256
 257 /* The function __do_global_ctors_aux is compiled twice (once in crtbegin.o
 258    and once in crtend.o).  It must be declared static to avoid a link
 259    error.  Here, we define __do_global_ctors as an externally callable
 260    function.  It is externally callable so that __main can invoke it when
 261    INVOKE__main is defined.  This has the additional effect of forcing cc1
 262    to switch to the .text section.  */
 263
 264 static void __do_global_ctors_aux (void);
 265 void
 266 __do_global_ctors (void)
 267 {
 268 #ifdef INVOKE__main  /* If __main won't actually call __do_global_ctors
 269                         then it doesn't matter what's inside the function.
 270                         The inside of __do_global_ctors_aux is called
 271                         automatically in that case.
 272                         And the Alliant fx2800 linker crashes
 273                         on this reference.  So prevent the crash.  */
 274   __do_global_ctors_aux ();
 275 #endif
 276 }
 277
 278 asm (INIT_SECTION_ASM_OP);      /* cc1 doesn't know that we are switching! */
 279
 280 /* On some svr4 systems, the initial .init section preamble code provided in
 281    crti.o may do something, such as bump the stack, which we have to
 282    undo before we reach the function prologue code for __do_global_ctors
 283    (directly below).  For such systems, define the macro INIT_SECTION_PREAMBLE
 284    to expand into the code needed to undo the actions of the crti.o file.  */
 285
 286 #ifdef INIT_SECTION_PREAMBLE
 287   INIT_SECTION_PREAMBLE;
 288 #endif
 289
 290 /* A routine to invoke all of the global constructors upon entry to the
 291    program.  We put this into the .init section (for systems that have
 292    such a thing) so that we can properly perform the construction of
 293    file-scope static-storage C++ objects within shared libraries.   */
 294
 295 static void
 296 __do_global_ctors_aux (void)    /* prologue goes in .init section */
 297 {
 298 #ifdef FORCE_INIT_SECTION_ALIGN
 299   FORCE_INIT_SECTION_ALIGN;     /* Explicit align before switch to .text */
 300 #endif
 301   asm (TEXT_SECTION_ASM_OP);    /* don't put epilogue and body in .init */
 302   DO_GLOBAL_CTORS_BODY;
 303   atexit (__do_global_dtors);
 304 }
 305
 306 #endif /* OBJECT_FORMAT_ELF */
 307
 308 #else /* defined(INIT_SECTION_ASM_OP) */
 309
 310 #ifdef HAS_INIT_SECTION
 311 /* This case is used by the Irix 6 port, which supports named sections but
 312    not an SVR4-style .fini section.  __do_global_dtors can be non-static
 313    in this case because we protect it with -hidden_symbol.  */
 314
 315 static char __EH_FRAME_BEGIN__[];
 316 static func_ptr __DTOR_LIST__[];
 317 void
 318 __do_global_dtors (void)
 319 {
 320   func_ptr *p;
 321   for (p = __DTOR_LIST__ + 1; *p; p++)
 322     (*p) ();
 323
 324 #ifdef EH_FRAME_SECTION_ASM_OP
 325   if (__deregister_frame_info)
 326     __deregister_frame_info (__EH_FRAME_BEGIN__);
 327 #endif
 328 }
 329
 330 #ifdef EH_FRAME_SECTION_ASM_OP
 331 /* Define a function here to call __register_frame.  crtend.o is linked in
 332    after libgcc.a, and hence can't call libgcc.a functions directly.  That
 333    can lead to unresolved function references.  */
 334 void
 335 __frame_dummy (void)
 336 {
 337   static struct object object;
 338   if (__register_frame_info)
 339     __register_frame_info (__EH_FRAME_BEGIN__, &object);
 340 }
 341 #endif
 342 #endif
 343
 344 #endif /* defined(INIT_SECTION_ASM_OP) */
 345
 346 /* Force cc1 to switch to .data section.  */
 347 static func_ptr force_to_data[1] __attribute__ ((__unused__)) = { };
 348
 349 /* NOTE:  In order to be able to support SVR4 shared libraries, we arrange
 350    to have one set of symbols { __CTOR_LIST__, __DTOR_LIST__, __CTOR_END__,
 351    __DTOR_END__ } per root executable and also one set of these symbols
 352    per shared library.  So in any given whole process image, we may have
 353    multiple definitions of each of these symbols.  In order to prevent
 354    these definitions from conflicting with one another, and in order to
 355    ensure that the proper lists are used for the initialization/finalization
 356    of each individual shared library (respectively), we give these symbols
 357    only internal (i.e. `static') linkage, and we also make it a point to
 358    refer to only the __CTOR_END__ symbol in crtend.o and the __DTOR_LIST__
 359    symbol in crtbegin.o, where they are defined.  */
 360
 361 /* The -1 is a flag to __do_global_[cd]tors
 362    indicating that this table does not start with a count of elements.  */
 363 #ifdef CTOR_LIST_BEGIN
 364 CTOR_LIST_BEGIN;
 365 #else
 366 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 367 STATIC func_ptr __CTOR_LIST__[1] __attribute__ ((__unused__))
 368   = { (func_ptr) (-1) };
 369 #endif
 370
 371 #ifdef DTOR_LIST_BEGIN
 372 DTOR_LIST_BEGIN;
 373 #else
 374 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 375 STATIC func_ptr __DTOR_LIST__[1] = { (func_ptr) (-1) };
 376 #endif
 377
 378 #ifdef EH_FRAME_SECTION_ASM_OP
 379 /* Stick a label at the beginning of the frame unwind info so we can register
 380    and deregister it with the exception handling library code.  */
 381
 382 asm (EH_FRAME_SECTION_ASM_OP);
 383 #ifdef INIT_SECTION_ASM_OP
 384 STATIC
 385 #endif
 386 char __EH_FRAME_BEGIN__[] = { };
 387 #endif /* EH_FRAME_SECTION_ASM_OP */
 388
 389 #endif /* defined(CRT_BEGIN) */
 390
 391 #ifdef CRT_END
 392
 393 #ifdef INIT_SECTION_ASM_OP
 394
 395 #ifdef OBJECT_FORMAT_ELF
 396
 397 static func_ptr __CTOR_END__[];
 398 static void
 399 __do_global_ctors_aux (void)
 400 {
 401   func_ptr *p;
 402   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 403     (*p) ();
 404 }
 405
 406 /* Stick a call to __do_global_ctors_aux into the .init section.  */
 407
 408 static void __attribute__ ((__unused__))
 409 init_dummy (void)
 410 {
 411   asm (INIT_SECTION_ASM_OP);
 412   CRT_CALL_STATIC_FUNCTION (__do_global_ctors_aux);
 413 #ifdef FORCE_INIT_SECTION_ALIGN
 414   FORCE_INIT_SECTION_ALIGN;
 415 #endif
 416   asm (TEXT_SECTION_ASM_OP);
 417 #ifdef CRT_END_INIT_DUMMY
 418   CRT_END_INIT_DUMMY;
 419 #endif
 420 }
 421
 422 #else  /* OBJECT_FORMAT_ELF */
 423
 424 /* Stick the real initialization code, followed by a normal sort of
 425    function epilogue at the very end of the .init section for this
 426    entire root executable file or for this entire shared library file.
 427
 428    Note that we use some tricks here to get *just* the body and just
 429    a function epilogue (but no function prologue) into the .init
 430    section of the crtend.o file.  Specifically, we switch to the .text
 431    section, start to define a function, and then we switch to the .init
 432    section just before the body code.
 433
 434    Earlier on, we put the corresponding function prologue into the .init
 435    section of the crtbegin.o file (which will be linked in first).
 436
 437    Note that we want to invoke all constructors for C++ file-scope static-
 438    storage objects AFTER any other possible initialization actions which
 439    may be performed by the code in the .init section contributions made by
 440    other libraries, etc.  That's because those other initializations may
 441    include setup operations for very primitive things (e.g. initializing
 442    the state of the floating-point coprocessor, etc.) which should be done
 443    before we start to execute any of the user's code.  */
 444
 445 static void
 446 __do_global_ctors_aux (void)    /* prologue goes in .text section */
 447 {
 448   asm (INIT_SECTION_ASM_OP);
 449   DO_GLOBAL_CTORS_BODY;
 450   atexit (__do_global_dtors);
 451 }                               /* epilogue and body go in .init section */
 452
 453 #ifdef FORCE_INIT_SECTION_ALIGN
 454 FORCE_INIT_SECTION_ALIGN;
 455 #endif
 456
 457 asm (TEXT_SECTION_ASM_OP);
 458
 459 #endif /* OBJECT_FORMAT_ELF */
 460
 461 #else /* defined(INIT_SECTION_ASM_OP) */
 462
 463 #ifdef HAS_INIT_SECTION
 464 /* This case is used by the Irix 6 port, which supports named sections but
 465    not an SVR4-style .init section.  __do_global_ctors can be non-static
 466    in this case because we protect it with -hidden_symbol.  */
 467 static func_ptr __CTOR_END__[];
 468 #ifdef EH_FRAME_SECTION_ASM_OP
 469 extern void __frame_dummy (void);
 470 #endif
 471 void
 472 __do_global_ctors (void)
 473 {
 474   func_ptr *p;
 475 #ifdef EH_FRAME_SECTION_ASM_OP
 476   __frame_dummy ();
 477 #endif
 478   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 479     (*p) ();
 480 }
 481 #endif
 482
 483 #endif /* defined(INIT_SECTION_ASM_OP) */
 484
 485 /* Force cc1 to switch to .data section.  */
 486 static func_ptr force_to_data[1] __attribute__ ((__unused__)) = { };
 487
 488 /* Put a word containing zero at the end of each of our two lists of function
 489    addresses.  Note that the words defined here go into the .ctors and .dtors
 490    sections of the crtend.o file, and since that file is always linked in
 491    last, these words naturally end up at the very ends of the two lists
 492    contained in these two sections.  */
 493
 494 #ifdef CTOR_LIST_END
 495 CTOR_LIST_END;
 496 #else
 497 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 498 STATIC func_ptr __CTOR_END__[1] = { (func_ptr) 0 };
 499 #endif
 500
 501 #ifdef DTOR_LIST_END
 502 DTOR_LIST_END;
 503 #else
 504 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 505 STATIC func_ptr __DTOR_END__[1] __attribute__ ((__unused__))
 506   = { (func_ptr) 0 };
 507 #endif
 508
 509 #ifdef EH_FRAME_SECTION_ASM_OP
 510 /* Terminate the frame unwind info section with a 4byte 0 as a sentinel;
 511    this would be the 'length' field in a real FDE.  */
 512
 513 typedef unsigned int ui32 __attribute__ ((mode (SI)));
 514 asm (EH_FRAME_SECTION_ASM_OP);
 515 STATIC ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
 516 #endif /* EH_FRAME_SECTION */
 517
 518 #endif /* defined(CRT_END) */
 519
 520 #else  /* OBJECT_FORMAT_MACHO */
 521
 522 /* For Mach-O format executables, we assume that the system's runtime is
 523    smart enough to handle constructors and destructors, but doesn't have
 524    an init section (if it can't even handle constructors/destructors
 525    you should be using INVOKE__main, not crtstuff). All we need to do
 526    is install/deinstall the frame information for exceptions. We do this
 527    by putting a constructor in crtbegin.o and a destructor in crtend.o.
 528
 529    crtend.o also puts in the terminating zero in the frame information
 530    segment. */
 531
 532 /* The crtstuff for other object formats use the symbol __EH_FRAME_BEGIN__
 533    to figure out the start of the exception frame, but here we use
 534    getsectbynamefromheader to find this value. Either method would work,
 535    but this method avoids creating any global symbols, which seems
 536    cleaner. */
 537
 538 #include <mach-o/ldsyms.h>
 539 extern const struct section *
 540   getsectbynamefromheader (const struct mach_header *,
 541                            const char *, const char *);
 542
 543 #ifdef CRT_BEGIN
 544
 545 static void __reg_frame_ctor (void) __attribute__ ((constructor));
 546
 547 static void
 548 __reg_frame_ctor (void)
 549 {
 550   static struct object object;
 551   const struct section *eh_frame;
 552
 553   eh_frame = getsectbynamefromheader (&_mh_execute_header,
 554                                       "__TEXT", "__eh_frame");
 555   __register_frame_info ((void *) eh_frame->addr, &object);
 556 }
 557
 558 #endif /* CRT_BEGIN */
 559
 560 #ifdef CRT_END
 561
 562 static void __dereg_frame_dtor (void) __attribute__ ((destructor));
 563
 564 static void
 565 __dereg_frame_dtor (void)
 566 {
 567   const struct section *eh_frame;
 568
 569   eh_frame = getsectbynamefromheader (&_mh_execute_header,
 570                                       "__TEXT", "__eh_frame");
 571   __deregister_frame_info ((void *) eh_frame->addr);
 572 }
 573
 574 /* Terminate the frame section with a final zero. */
 575
 576 /* Force cc1 to switch to .data section.  */
 577 static void * force_to_data[1] __attribute__ ((__unused__)) = { };
 578
 579 typedef unsigned int ui32 __attribute__ ((mode (SI)));
 580 asm (EH_FRAME_SECTION_ASM_OP);
 581 static ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
 582
 583 #endif /* CRT_END */
 584
 585 #endif /* OBJECT_FORMAT_MACHO */
 586