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, 94, 95, 96, 97, 1998 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 #if !defined (EH_FRAME_SECTION_ASM_OP) && defined (DWARF2_UNWIND_INFO) && defined(ASM_OUTPUT_SECTION_NAME)
 112 #define EH_FRAME_SECTION_ASM_OP ".section\t.eh_frame,\"aw\""
 113 #endif
 114
 115 #ifdef OBJECT_FORMAT_ELF
 116
 117 /*  Declare a pointer to void function type.  */
 118 typedef void (*func_ptr) (void);
 119 #define STATIC static
 120
 121 #else  /* OBJECT_FORMAT_ELF */
 122
 123 #include "gbl-ctors.h"
 124
 125 #ifndef ON_EXIT
 126 #define ON_EXIT(a, b)
 127 #endif
 128 #define STATIC
 129
 130 #endif /* OBJECT_FORMAT_ELF */
 131
 132 #ifdef CRT_BEGIN
 133
 134 #ifdef INIT_SECTION_ASM_OP
 135
 136 #ifdef OBJECT_FORMAT_ELF
 137
 138 /* Run all the global destructors on exit from the program.  */
 139
 140 /* Some systems place the number of pointers in the first word of the
 141    table.  On SVR4 however, that word is -1.  In all cases, the table is
 142    null-terminated.  On SVR4, we start from the beginning of the list and
 143    invoke each per-compilation-unit destructor routine in order
 144    until we find that null.
 145
 146    Note that this function MUST be static.  There will be one of these
 147    functions in each root executable and one in each shared library, but
 148    although they all have the same code, each one is unique in that it
 149    refers to one particular associated `__DTOR_LIST__' which belongs to the
 150    same particular root executable or shared library file.
 151
 152    On some systems, this routine is run more than once from the .fini,
 153    when exit is called recursively, so we arrange to remember where in
 154    the list we left off processing, and we resume at that point,
 155    should we be re-invoked.  */
 156
 157 static char __EH_FRAME_BEGIN__[];
 158 static func_ptr __DTOR_LIST__[];
 159 static void
 160 __do_global_dtors_aux (void)
 161 {
 162   static func_ptr *p = __DTOR_LIST__ + 1;
 163   static int completed = 0;
 164
 165   if (completed)
 166     return;
 167
 168   while (*p)
 169     {
 170       p++;
 171       (*(p-1)) ();
 172     }
 173
 174 #ifdef EH_FRAME_SECTION_ASM_OP
 175   if (__deregister_frame_info)
 176     __deregister_frame_info (__EH_FRAME_BEGIN__);
 177 #endif
 178   completed = 1;
 179 }
 180
 181
 182 /* Stick a call to __do_global_dtors_aux into the .fini section.  */
 183
 184 static void __attribute__ ((__unused__))
 185 fini_dummy (void)
 186 {
 187   asm (FINI_SECTION_ASM_OP);
 188   __do_global_dtors_aux ();
 189 #ifdef FORCE_FINI_SECTION_ALIGN
 190   FORCE_FINI_SECTION_ALIGN;
 191 #endif
 192   asm (TEXT_SECTION_ASM_OP);
 193 }
 194
 195 #ifdef EH_FRAME_SECTION_ASM_OP
 196 /* Stick a call to __register_frame_info into the .init section.  For some
 197    reason calls with no arguments work more reliably in .init, so stick the
 198    call in another function.  */
 199
 200 static void
 201 frame_dummy (void)
 202 {
 203   static struct object object;
 204   if (__register_frame_info)
 205     __register_frame_info (__EH_FRAME_BEGIN__, &object);
 206 }
 207
 208 static void __attribute__ ((__unused__))
 209 init_dummy (void)
 210 {
 211   asm (INIT_SECTION_ASM_OP);
 212   frame_dummy ();
 213 #ifdef FORCE_INIT_SECTION_ALIGN
 214   FORCE_INIT_SECTION_ALIGN;
 215 #endif
 216   asm (TEXT_SECTION_ASM_OP);
 217 }
 218 #endif /* EH_FRAME_SECTION_ASM_OP */
 219
 220 #else  /* OBJECT_FORMAT_ELF */
 221
 222 /* The function __do_global_ctors_aux is compiled twice (once in crtbegin.o
 223    and once in crtend.o).  It must be declared static to avoid a link
 224    error.  Here, we define __do_global_ctors as an externally callable
 225    function.  It is externally callable so that __main can invoke it when
 226    INVOKE__main is defined.  This has the additional effect of forcing cc1
 227    to switch to the .text section.  */
 228
 229 static void __do_global_ctors_aux ();
 230 void
 231 __do_global_ctors (void)
 232 {
 233 #ifdef INVOKE__main  /* If __main won't actually call __do_global_ctors
 234                         then it doesn't matter what's inside the function.
 235                         The inside of __do_global_ctors_aux is called
 236                         automatically in that case.
 237                         And the Alliant fx2800 linker crashes
 238                         on this reference.  So prevent the crash.  */
 239   __do_global_ctors_aux ();
 240 #endif
 241 }
 242
 243 asm (INIT_SECTION_ASM_OP);      /* cc1 doesn't know that we are switching! */
 244
 245 /* On some svr4 systems, the initial .init section preamble code provided in
 246    crti.o may do something, such as bump the stack, which we have to
 247    undo before we reach the function prologue code for __do_global_ctors
 248    (directly below).  For such systems, define the macro INIT_SECTION_PREAMBLE
 249    to expand into the code needed to undo the actions of the crti.o file.  */
 250
 251 #ifdef INIT_SECTION_PREAMBLE
 252   INIT_SECTION_PREAMBLE;
 253 #endif
 254
 255 /* A routine to invoke all of the global constructors upon entry to the
 256    program.  We put this into the .init section (for systems that have
 257    such a thing) so that we can properly perform the construction of
 258    file-scope static-storage C++ objects within shared libraries.   */
 259
 260 static void
 261 __do_global_ctors_aux (void)    /* prologue goes in .init section */
 262 {
 263 #ifdef FORCE_INIT_SECTION_ALIGN
 264   FORCE_INIT_SECTION_ALIGN;     /* Explicit align before switch to .text */
 265 #endif
 266   asm (TEXT_SECTION_ASM_OP);    /* don't put epilogue and body in .init */
 267   DO_GLOBAL_CTORS_BODY;
 268   ON_EXIT (__do_global_dtors, 0);
 269 }
 270
 271 #endif /* OBJECT_FORMAT_ELF */
 272
 273 #else /* defined(INIT_SECTION_ASM_OP) */
 274
 275 #ifdef HAS_INIT_SECTION
 276 /* This case is used by the Irix 6 port, which supports named sections but
 277    not an SVR4-style .fini section.  __do_global_dtors can be non-static
 278    in this case because we protect it with -hidden_symbol.  */
 279
 280 static char __EH_FRAME_BEGIN__[];
 281 static func_ptr __DTOR_LIST__[];
 282 void
 283 __do_global_dtors (void)
 284 {
 285   func_ptr *p;
 286   for (p = __DTOR_LIST__ + 1; *p; p++)
 287     (*p) ();
 288
 289 #ifdef EH_FRAME_SECTION_ASM_OP
 290   if (__deregister_frame_info)
 291     __deregister_frame_info (__EH_FRAME_BEGIN__);
 292 #endif
 293 }
 294
 295 #ifdef EH_FRAME_SECTION_ASM_OP
 296 /* Define a function here to call __register_frame.  crtend.o is linked in
 297    after libgcc.a, and hence can't call libgcc.a functions directly.  That
 298    can lead to unresolved function references.  */
 299 void
 300 __frame_dummy (void)
 301 {
 302   static struct object object;
 303   if (__register_frame_info)
 304     __register_frame_info (__EH_FRAME_BEGIN__, &object);
 305 }
 306 #endif
 307 #endif
 308
 309 #endif /* defined(INIT_SECTION_ASM_OP) */
 310
 311 /* Force cc1 to switch to .data section.  */
 312 static func_ptr force_to_data[0] __attribute__ ((__unused__)) = { };
 313
 314 /* NOTE:  In order to be able to support SVR4 shared libraries, we arrange
 315    to have one set of symbols { __CTOR_LIST__, __DTOR_LIST__, __CTOR_END__,
 316    __DTOR_END__ } per root executable and also one set of these symbols
 317    per shared library.  So in any given whole process image, we may have
 318    multiple definitions of each of these symbols.  In order to prevent
 319    these definitions from conflicting with one another, and in order to
 320    ensure that the proper lists are used for the initialization/finalization
 321    of each individual shared library (respectively), we give these symbols
 322    only internal (i.e. `static') linkage, and we also make it a point to
 323    refer to only the __CTOR_END__ symbol in crtend.o and the __DTOR_LIST__
 324    symbol in crtbegin.o, where they are defined.  */
 325
 326 /* The -1 is a flag to __do_global_[cd]tors
 327    indicating that this table does not start with a count of elements.  */
 328 #ifdef CTOR_LIST_BEGIN
 329 CTOR_LIST_BEGIN;
 330 #else
 331 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 332 STATIC func_ptr __CTOR_LIST__[1] __attribute__ ((__unused__))
 333   = { (func_ptr) (-1) };
 334 #endif
 335
 336 #ifdef DTOR_LIST_BEGIN
 337 DTOR_LIST_BEGIN;
 338 #else
 339 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 340 STATIC func_ptr __DTOR_LIST__[1] = { (func_ptr) (-1) };
 341 #endif
 342
 343 #ifdef EH_FRAME_SECTION_ASM_OP
 344 /* Stick a label at the beginning of the frame unwind info so we can register
 345    and deregister it with the exception handling library code.  */
 346
 347 asm (EH_FRAME_SECTION_ASM_OP);
 348 #ifdef INIT_SECTION_ASM_OP
 349 STATIC
 350 #endif
 351 char __EH_FRAME_BEGIN__[] = { };
 352 #endif /* EH_FRAME_SECTION_ASM_OP */
 353
 354 #endif /* defined(CRT_BEGIN) */
 355
 356 #ifdef CRT_END
 357
 358 #ifdef INIT_SECTION_ASM_OP
 359
 360 #ifdef OBJECT_FORMAT_ELF
 361
 362 static func_ptr __CTOR_END__[];
 363 static void
 364 __do_global_ctors_aux (void)
 365 {
 366   func_ptr *p;
 367   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 368     (*p) ();
 369 }
 370
 371 /* Stick a call to __do_global_ctors_aux into the .init section.  */
 372
 373 static void __attribute__ ((__unused__))
 374 init_dummy (void)
 375 {
 376   asm (INIT_SECTION_ASM_OP);
 377   __do_global_ctors_aux ();
 378 #ifdef FORCE_INIT_SECTION_ALIGN
 379   FORCE_INIT_SECTION_ALIGN;
 380 #endif
 381   asm (TEXT_SECTION_ASM_OP);
 382
 383 /* This is a kludge. The i386 GNU/Linux dynamic linker needs ___brk_addr,
 384    __environ and atexit (). We have to make sure they are in the .dynsym
 385    section. We accomplish it by making a dummy call here. This
 386    code is never reached.  */
 387
 388 #if defined(__linux__) && defined(__PIC__) && defined(__i386__)
 389   {
 390     extern void *___brk_addr;
 391     extern char **__environ;
 392
 393     ___brk_addr = __environ;
 394     atexit ();
 395   }
 396 #endif
 397 }
 398
 399 #else  /* OBJECT_FORMAT_ELF */
 400
 401 /* Stick the real initialization code, followed by a normal sort of
 402    function epilogue at the very end of the .init section for this
 403    entire root executable file or for this entire shared library file.
 404
 405    Note that we use some tricks here to get *just* the body and just
 406    a function epilogue (but no function prologue) into the .init
 407    section of the crtend.o file.  Specifically, we switch to the .text
 408    section, start to define a function, and then we switch to the .init
 409    section just before the body code.
 410
 411    Earlier on, we put the corresponding function prologue into the .init
 412    section of the crtbegin.o file (which will be linked in first).
 413
 414    Note that we want to invoke all constructors for C++ file-scope static-
 415    storage objects AFTER any other possible initialization actions which
 416    may be performed by the code in the .init section contributions made by
 417    other libraries, etc.  That's because those other initializations may
 418    include setup operations for very primitive things (e.g. initializing
 419    the state of the floating-point coprocessor, etc.) which should be done
 420    before we start to execute any of the user's code.  */
 421
 422 static void
 423 __do_global_ctors_aux (void)    /* prologue goes in .text section */
 424 {
 425   asm (INIT_SECTION_ASM_OP);
 426   DO_GLOBAL_CTORS_BODY;
 427   ON_EXIT (__do_global_dtors, 0);
 428 }                               /* epilogue and body go in .init section */
 429
 430 #ifdef FORCE_INIT_SECTION_ALIGN
 431 FORCE_INIT_SECTION_ALIGN;
 432 #endif
 433
 434 asm (TEXT_SECTION_ASM_OP);
 435
 436 #endif /* OBJECT_FORMAT_ELF */
 437
 438 #else /* defined(INIT_SECTION_ASM_OP) */
 439
 440 #ifdef HAS_INIT_SECTION
 441 /* This case is used by the Irix 6 port, which supports named sections but
 442    not an SVR4-style .init section.  __do_global_ctors can be non-static
 443    in this case because we protect it with -hidden_symbol.  */
 444 static func_ptr __CTOR_END__[];
 445 #ifdef EH_FRAME_SECTION_ASM_OP
 446 extern void __frame_dummy (void);
 447 #endif
 448 void
 449 __do_global_ctors (void)
 450 {
 451   func_ptr *p;
 452 #ifdef EH_FRAME_SECTION_ASM_OP
 453   __frame_dummy ();
 454 #endif
 455   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 456     (*p) ();
 457 }
 458 #endif
 459
 460 #endif /* defined(INIT_SECTION_ASM_OP) */
 461
 462 /* Force cc1 to switch to .data section.  */
 463 static func_ptr force_to_data[0] __attribute__ ((__unused__)) = { };
 464
 465 /* Put a word containing zero at the end of each of our two lists of function
 466    addresses.  Note that the words defined here go into the .ctors and .dtors
 467    sections of the crtend.o file, and since that file is always linked in
 468    last, these words naturally end up at the very ends of the two lists
 469    contained in these two sections.  */
 470
 471 #ifdef CTOR_LIST_END
 472 CTOR_LIST_END;
 473 #else
 474 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 475 STATIC func_ptr __CTOR_END__[1] = { (func_ptr) 0 };
 476 #endif
 477
 478 #ifdef DTOR_LIST_END
 479 DTOR_LIST_END;
 480 #else
 481 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 482 STATIC func_ptr __DTOR_END__[1] __attribute__ ((__unused__))
 483   = { (func_ptr) 0 };
 484 #endif
 485
 486 #ifdef EH_FRAME_SECTION_ASM_OP
 487 /* Terminate the frame unwind info section with a 4byte 0 as a sentinel;
 488    this would be the 'length' field in a real FDE.  */
 489
 490 typedef unsigned int ui32 __attribute__ ((mode (SI)));
 491 asm (EH_FRAME_SECTION_ASM_OP);
 492 STATIC ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
 493 #endif /* EH_FRAME_SECTION */
 494
 495 #endif /* defined(CRT_END) */
 496
 497 #else  /* OBJECT_FORMAT_MACHO */
 498
 499 /* For Mach-O format executables, we assume that the system's runtime is
 500    smart enough to handle constructors and destructors, but doesn't have
 501    an init section (if it can't even handle constructors/destructors
 502    you should be using INVOKE__main, not crtstuff). All we need to do
 503    is install/deinstall the frame information for exceptions. We do this
 504    by putting a constructor in crtbegin.o and a destructor in crtend.o.
 505
 506    crtend.o also puts in the terminating zero in the frame information
 507    segment. */
 508
 509 /* The crtstuff for other object formats use the symbol __EH_FRAME_BEGIN__
 510    to figure out the start of the exception frame, but here we use
 511    getsectbynamefromheader to find this value. Either method would work,
 512    but this method avoids creating any global symbols, which seems
 513    cleaner. */
 514
 515 #include <mach-o/ldsyms.h>
 516 extern const struct section *
 517   getsectbynamefromheader (const struct mach_header *,
 518                            const char *, const char *);
 519
 520 #ifdef CRT_BEGIN
 521
 522 static void __reg_frame_ctor () __attribute__ ((constructor));
 523
 524 static void
 525 __reg_frame_ctor (void)
 526 {
 527   static struct object object;
 528   const struct section *eh_frame;
 529
 530   eh_frame = getsectbynamefromheader (&_mh_execute_header,
 531                                       "__TEXT", "__eh_frame");
 532   __register_frame_info ((void *) eh_frame->addr, &object);
 533 }
 534
 535 #endif /* CRT_BEGIN */
 536
 537 #ifdef CRT_END
 538
 539 static void __dereg_frame_dtor () __attribute__ ((destructor));
 540
 541 static
 542 void
 543 __dereg_frame_dtor (void)
 544 {
 545   const struct section *eh_frame;
 546
 547   eh_frame = getsectbynamefromheader (&_mh_execute_header,
 548                                       "__TEXT", "__eh_frame");
 549   __deregister_frame_info ((void *) eh_frame->addr);
 550 }
 551
 552 /* Terminate the frame section with a final zero. */
 553
 554 /* Force cc1 to switch to .data section.  */
 555 static void * force_to_data[0] __attribute__ ((__unused__)) = { };
 556
 557 typedef unsigned int ui32 __attribute__ ((mode (SI)));
 558 asm (EH_FRAME_SECTION_ASM_OP);
 559 static ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
 560
 561 #endif /* CRT_END */
 562
 563 #endif /* OBJECT_FORMAT_MACHO */
 564