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 #ifndef OBJECT_FORMAT_MACHO
  60
  61 /* Provide default definitions for the pseudo-ops used to switch to the
  62    .ctors and .dtors sections.
  63
  64    Note that we want to give these sections the SHF_WRITE attribute
  65    because these sections will actually contain data (i.e. tables of
  66    addresses of functions in the current root executable or shared library
  67    file) and, in the case of a shared library, the relocatable addresses
  68    will have to be properly resolved/relocated (and then written into) by
  69    the dynamic linker when it actually attaches the given shared library
  70    to the executing process.  (Note that on SVR4, you may wish to use the
  71    `-z text' option to the ELF linker, when building a shared library, as
  72    an additional check that you are doing everything right.  But if you do
  73    use the `-z text' option when building a shared library, you will get
  74    errors unless the .ctors and .dtors sections are marked as writable
  75    via the SHF_WRITE attribute.)  */
  76
  77 #ifndef CTORS_SECTION_ASM_OP
  78 #define CTORS_SECTION_ASM_OP    ".section\t.ctors,\"aw\""
  79 #endif
  80 #ifndef DTORS_SECTION_ASM_OP
  81 #define DTORS_SECTION_ASM_OP    ".section\t.dtors,\"aw\""
  82 #endif
  83 #if !defined (EH_FRAME_SECTION_ASM_OP) && defined (DWARF2_UNWIND_INFO) && defined(ASM_OUTPUT_SECTION_NAME)
  84 #define EH_FRAME_SECTION_ASM_OP ".section\t.eh_frame,\"aw\""
  85 #endif
  86
  87 #ifdef OBJECT_FORMAT_ELF
  88
  89 /*  Declare a pointer to void function type.  */
  90 typedef void (*func_ptr) (void);
  91 #define STATIC static
  92
  93 #else  /* OBJECT_FORMAT_ELF */
  94
  95 #include "gbl-ctors.h"
  96
  97 #ifndef ON_EXIT
  98 #define ON_EXIT(a, b)
  99 #endif
 100 #define STATIC
 101
 102 #endif /* OBJECT_FORMAT_ELF */
 103
 104 #ifdef CRT_BEGIN
 105
 106 #ifdef INIT_SECTION_ASM_OP
 107
 108 #ifdef OBJECT_FORMAT_ELF
 109
 110 /* Run all the global destructors on exit from the program.  */
 111
 112 /* Some systems place the number of pointers in the first word of the
 113    table.  On SVR4 however, that word is -1.  In all cases, the table is
 114    null-terminated.  On SVR4, we start from the beginning of the list and
 115    invoke each per-compilation-unit destructor routine in order
 116    until we find that null.
 117
 118    Note that this function MUST be static.  There will be one of these
 119    functions in each root executable and one in each shared library, but
 120    although they all have the same code, each one is unique in that it
 121    refers to one particular associated `__DTOR_LIST__' which belongs to the
 122    same particular root executable or shared library file.
 123
 124    On some systems, this routine is run more than once from the .fini,
 125    when exit is called recursively, so we arrange to remember where in
 126    the list we left off processing, and we resume at that point,
 127    should we be re-invoked.  */
 128
 129 static char __EH_FRAME_BEGIN__[];
 130 static func_ptr __DTOR_LIST__[];
 131 static void
 132 __do_global_dtors_aux ()
 133 {
 134   static func_ptr *p = __DTOR_LIST__ + 1;
 135   static int completed = 0;
 136
 137   if (completed)
 138     return;
 139
 140   while (*p)
 141     {
 142       p++;
 143       (*(p-1)) ();
 144     }
 145
 146 #ifdef EH_FRAME_SECTION_ASM_OP
 147   __deregister_frame_info (__EH_FRAME_BEGIN__);
 148 #endif
 149   completed = 1;
 150 }
 151
 152
 153 /* Stick a call to __do_global_dtors_aux into the .fini section.  */
 154
 155 static void __attribute__ ((__unused__))
 156 fini_dummy ()
 157 {
 158   asm (FINI_SECTION_ASM_OP);
 159   __do_global_dtors_aux ();
 160 #ifdef FORCE_FINI_SECTION_ALIGN
 161   FORCE_FINI_SECTION_ALIGN;
 162 #endif
 163   asm (TEXT_SECTION_ASM_OP);
 164 }
 165
 166 #ifdef EH_FRAME_SECTION_ASM_OP
 167 /* Stick a call to __register_frame_info into the .init section.  For some
 168    reason calls with no arguments work more reliably in .init, so stick the
 169    call in another function.  */
 170
 171 static void
 172 frame_dummy ()
 173 {
 174   static struct object object;
 175   __register_frame_info (__EH_FRAME_BEGIN__, &object);
 176 }
 177
 178 static void __attribute__ ((__unused__))
 179 init_dummy ()
 180 {
 181   asm (INIT_SECTION_ASM_OP);
 182   frame_dummy ();
 183 #ifdef FORCE_INIT_SECTION_ALIGN
 184   FORCE_INIT_SECTION_ALIGN;
 185 #endif
 186   asm (TEXT_SECTION_ASM_OP);
 187 }
 188 #endif /* EH_FRAME_SECTION_ASM_OP */
 189
 190 #else  /* OBJECT_FORMAT_ELF */
 191
 192 /* The function __do_global_ctors_aux is compiled twice (once in crtbegin.o
 193    and once in crtend.o).  It must be declared static to avoid a link
 194    error.  Here, we define __do_global_ctors as an externally callable
 195    function.  It is externally callable so that __main can invoke it when
 196    INVOKE__main is defined.  This has the additional effect of forcing cc1
 197    to switch to the .text section.  */
 198
 199 static void __do_global_ctors_aux ();
 200 void __do_global_ctors ()
 201 {
 202 #ifdef INVOKE__main  /* If __main won't actually call __do_global_ctors
 203                         then it doesn't matter what's inside the function.
 204                         The inside of __do_global_ctors_aux is called
 205                         automatically in that case.
 206                         And the Alliant fx2800 linker crashes
 207                         on this reference.  So prevent the crash.  */
 208   __do_global_ctors_aux ();
 209 #endif
 210 }
 211
 212 asm (INIT_SECTION_ASM_OP);      /* cc1 doesn't know that we are switching! */
 213
 214 /* On some svr4 systems, the initial .init section preamble code provided in
 215    crti.o may do something, such as bump the stack, which we have to
 216    undo before we reach the function prologue code for __do_global_ctors
 217    (directly below).  For such systems, define the macro INIT_SECTION_PREAMBLE
 218    to expand into the code needed to undo the actions of the crti.o file.  */
 219
 220 #ifdef INIT_SECTION_PREAMBLE
 221   INIT_SECTION_PREAMBLE;
 222 #endif
 223
 224 /* A routine to invoke all of the global constructors upon entry to the
 225    program.  We put this into the .init section (for systems that have
 226    such a thing) so that we can properly perform the construction of
 227    file-scope static-storage C++ objects within shared libraries.   */
 228
 229 static void
 230 __do_global_ctors_aux ()        /* prologue goes in .init section */
 231 {
 232 #ifdef FORCE_INIT_SECTION_ALIGN
 233   FORCE_INIT_SECTION_ALIGN;     /* Explicit align before switch to .text */
 234 #endif
 235   asm (TEXT_SECTION_ASM_OP);    /* don't put epilogue and body in .init */
 236   DO_GLOBAL_CTORS_BODY;
 237   ON_EXIT (__do_global_dtors, 0);
 238 }
 239
 240 #endif /* OBJECT_FORMAT_ELF */
 241
 242 #else /* defined(INIT_SECTION_ASM_OP) */
 243
 244 #ifdef HAS_INIT_SECTION
 245 /* This case is used by the Irix 6 port, which supports named sections but
 246    not an SVR4-style .fini section.  __do_global_dtors can be non-static
 247    in this case because we protect it with -hidden_symbol.  */
 248
 249 static char __EH_FRAME_BEGIN__[];
 250 static func_ptr __DTOR_LIST__[];
 251 void
 252 __do_global_dtors ()
 253 {
 254   func_ptr *p;
 255   for (p = __DTOR_LIST__ + 1; *p; p++)
 256     (*p) ();
 257
 258 #ifdef EH_FRAME_SECTION_ASM_OP
 259   __deregister_frame_info (__EH_FRAME_BEGIN__);
 260 #endif
 261 }
 262
 263 #ifdef EH_FRAME_SECTION_ASM_OP
 264 /* Define a function here to call __register_frame.  crtend.o is linked in
 265    after libgcc.a, and hence can't call libgcc.a functions directly.  That
 266    can lead to unresolved function references.  */
 267 void
 268 __frame_dummy ()
 269 {
 270   static struct object object;
 271   __register_frame_info (__EH_FRAME_BEGIN__, &object);
 272 }
 273 #endif
 274 #endif
 275
 276 #endif /* defined(INIT_SECTION_ASM_OP) */
 277
 278 /* Force cc1 to switch to .data section.  */
 279 static func_ptr force_to_data[0] __attribute__ ((__unused__)) = { };
 280
 281 /* NOTE:  In order to be able to support SVR4 shared libraries, we arrange
 282    to have one set of symbols { __CTOR_LIST__, __DTOR_LIST__, __CTOR_END__,
 283    __DTOR_END__ } per root executable and also one set of these symbols
 284    per shared library.  So in any given whole process image, we may have
 285    multiple definitions of each of these symbols.  In order to prevent
 286    these definitions from conflicting with one another, and in order to
 287    ensure that the proper lists are used for the initialization/finalization
 288    of each individual shared library (respectively), we give these symbols
 289    only internal (i.e. `static') linkage, and we also make it a point to
 290    refer to only the __CTOR_END__ symbol in crtend.o and the __DTOR_LIST__
 291    symbol in crtbegin.o, where they are defined.  */
 292
 293 /* The -1 is a flag to __do_global_[cd]tors
 294    indicating that this table does not start with a count of elements.  */
 295 #ifdef CTOR_LIST_BEGIN
 296 CTOR_LIST_BEGIN;
 297 #else
 298 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 299 STATIC func_ptr __CTOR_LIST__[1] __attribute__ ((__unused__))
 300   = { (func_ptr) (-1) };
 301 #endif
 302
 303 #ifdef DTOR_LIST_BEGIN
 304 DTOR_LIST_BEGIN;
 305 #else
 306 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 307 STATIC func_ptr __DTOR_LIST__[1] = { (func_ptr) (-1) };
 308 #endif
 309
 310 #ifdef EH_FRAME_SECTION_ASM_OP
 311 /* Stick a label at the beginning of the frame unwind info so we can register
 312    and deregister it with the exception handling library code.  */
 313
 314 asm (EH_FRAME_SECTION_ASM_OP);
 315 #ifdef INIT_SECTION_ASM_OP
 316 STATIC
 317 #endif
 318 char __EH_FRAME_BEGIN__[] = { };
 319 #endif /* EH_FRAME_SECTION_ASM_OP */
 320
 321 #endif /* defined(CRT_BEGIN) */
 322
 323 #ifdef CRT_END
 324
 325 #ifdef INIT_SECTION_ASM_OP
 326
 327 #ifdef OBJECT_FORMAT_ELF
 328
 329 static func_ptr __CTOR_END__[];
 330 static void
 331 __do_global_ctors_aux ()
 332 {
 333   func_ptr *p;
 334   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 335     (*p) ();
 336 }
 337
 338 /* Stick a call to __do_global_ctors_aux into the .init section.  */
 339
 340 static void __attribute__ ((__unused__))
 341 init_dummy ()
 342 {
 343   asm (INIT_SECTION_ASM_OP);
 344   __do_global_ctors_aux ();
 345 #ifdef FORCE_INIT_SECTION_ALIGN
 346   FORCE_INIT_SECTION_ALIGN;
 347 #endif
 348   asm (TEXT_SECTION_ASM_OP);
 349
 350 /* This is a kludge. The i386 GNU/Linux dynamic linker needs ___brk_addr,
 351    __environ and atexit (). We have to make sure they are in the .dynsym
 352    section. We accomplish it by making a dummy call here. This
 353    code is never reached.  */
 354
 355 #if defined(__linux__) && defined(__PIC__) && defined(__i386__)
 356   {
 357     extern void *___brk_addr;
 358     extern char **__environ;
 359
 360     ___brk_addr = __environ;
 361     atexit ();
 362   }
 363 #endif
 364 }
 365
 366 #else  /* OBJECT_FORMAT_ELF */
 367
 368 /* Stick the real initialization code, followed by a normal sort of
 369    function epilogue at the very end of the .init section for this
 370    entire root executable file or for this entire shared library file.
 371
 372    Note that we use some tricks here to get *just* the body and just
 373    a function epilogue (but no function prologue) into the .init
 374    section of the crtend.o file.  Specifically, we switch to the .text
 375    section, start to define a function, and then we switch to the .init
 376    section just before the body code.
 377
 378    Earlier on, we put the corresponding function prologue into the .init
 379    section of the crtbegin.o file (which will be linked in first).
 380
 381    Note that we want to invoke all constructors for C++ file-scope static-
 382    storage objects AFTER any other possible initialization actions which
 383    may be performed by the code in the .init section contributions made by
 384    other libraries, etc.  That's because those other initializations may
 385    include setup operations for very primitive things (e.g. initializing
 386    the state of the floating-point coprocessor, etc.) which should be done
 387    before we start to execute any of the user's code.  */
 388
 389 static void
 390 __do_global_ctors_aux ()        /* prologue goes in .text section */
 391 {
 392   asm (INIT_SECTION_ASM_OP);
 393   DO_GLOBAL_CTORS_BODY;
 394   ON_EXIT (__do_global_dtors, 0);
 395 }                               /* epilogue and body go in .init section */
 396
 397 #ifdef FORCE_INIT_SECTION_ALIGN
 398 FORCE_INIT_SECTION_ALIGN;
 399 #endif
 400
 401 asm (TEXT_SECTION_ASM_OP);
 402
 403 #endif /* OBJECT_FORMAT_ELF */
 404
 405 #else /* defined(INIT_SECTION_ASM_OP) */
 406
 407 #ifdef HAS_INIT_SECTION
 408 /* This case is used by the Irix 6 port, which supports named sections but
 409    not an SVR4-style .init section.  __do_global_ctors can be non-static
 410    in this case because we protect it with -hidden_symbol.  */
 411 static func_ptr __CTOR_END__[];
 412 #ifdef EH_FRAME_SECTION_ASM_OP
 413 extern void __frame_dummy (void);
 414 #endif
 415 void
 416 __do_global_ctors ()
 417 {
 418   func_ptr *p;
 419 #ifdef EH_FRAME_SECTION_ASM_OP
 420   __frame_dummy ();
 421 #endif
 422   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 423     (*p) ();
 424 }
 425 #endif
 426
 427 #endif /* defined(INIT_SECTION_ASM_OP) */
 428
 429 /* Force cc1 to switch to .data section.  */
 430 static func_ptr force_to_data[0] __attribute__ ((__unused__)) = { };
 431
 432 /* Put a word containing zero at the end of each of our two lists of function
 433    addresses.  Note that the words defined here go into the .ctors and .dtors
 434    sections of the crtend.o file, and since that file is always linked in
 435    last, these words naturally end up at the very ends of the two lists
 436    contained in these two sections.  */
 437
 438 #ifdef CTOR_LIST_END
 439 CTOR_LIST_END;
 440 #else
 441 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 442 STATIC func_ptr __CTOR_END__[1] = { (func_ptr) 0 };
 443 #endif
 444
 445 #ifdef DTOR_LIST_END
 446 DTOR_LIST_END;
 447 #else
 448 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 449 STATIC func_ptr __DTOR_END__[1] __attribute__ ((__unused__))
 450   = { (func_ptr) 0 };
 451 #endif
 452
 453 #ifdef EH_FRAME_SECTION_ASM_OP
 454 /* Terminate the frame unwind info section with a 4byte 0 as a sentinel;
 455    this would be the 'length' field in a real FDE.  */
 456
 457 typedef unsigned int ui32 __attribute__ ((mode (SI)));
 458 asm (EH_FRAME_SECTION_ASM_OP);
 459 STATIC ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
 460 #endif /* EH_FRAME_SECTION */
 461
 462 #endif /* defined(CRT_END) */
 463
 464 #else  /* OBJECT_FORMAT_MACHO */
 465
 466 /* For Mach-O format executables, we assume that the system's runtime is
 467    smart enough to handle constructors and destructors, but doesn't have
 468    an init section (if it can't even handle constructors/destructors
 469    you should be using INVOKE__main, not crtstuff). All we need to do
 470    is install/deinstall the frame information for exceptions. We do this
 471    by putting a constructor in crtbegin.o and a destructor in crtend.o.
 472
 473    crtend.o also puts in the terminating zero in the frame information
 474    segment. */
 475
 476 /* The crtstuff for other object formats use the symbol __EH_FRAME_BEGIN__
 477    to figure out the start of the exception frame, but here we use
 478    getsectbynamefromheader to find this value. Either method would work,
 479    but this method avoids creating any global symbols, which seems
 480    cleaner. */
 481
 482 #include <mach-o/ldsyms.h>
 483 extern const struct section *
 484   getsectbynamefromheader (const struct mach_header *,
 485                            const char *, const char *);
 486
 487 #ifdef CRT_BEGIN
 488
 489 static void __reg_frame_ctor () __attribute__ ((constructor));
 490
 491 static void
 492 __reg_frame_ctor ()
 493 {
 494   static struct object object;
 495   const struct section *eh_frame;
 496
 497   eh_frame = getsectbynamefromheader (&_mh_execute_header,
 498                                       "__TEXT", "__eh_frame");
 499   __register_frame_info ((void *) eh_frame->addr, &object);
 500 }
 501
 502 #endif /* CRT_BEGIN */
 503
 504 #ifdef CRT_END
 505
 506 static void __dereg_frame_dtor () __attribute__ ((destructor));
 507
 508 static
 509 void __dereg_frame_dtor ()
 510 {
 511   const struct section *eh_frame;
 512
 513   eh_frame = getsectbynamefromheader (&_mh_execute_header,
 514                                       "__TEXT", "__eh_frame");
 515   __deregister_frame_info ((void *) eh_frame->addr);
 516 }
 517
 518 /* Terminate the frame section with a final zero. */
 519
 520 /* Force cc1 to switch to .data section.  */
 521 static void * force_to_data[0] __attribute__ ((__unused__)) = { };
 522
 523 typedef unsigned int ui32 __attribute__ ((mode (SI)));
 524 asm (EH_FRAME_SECTION_ASM_OP);
 525 static ui32 __FRAME_END__[] __attribute__ ((__unused__)) = { 0 };
 526
 527 #endif /* CRT_END */
 528
 529 #endif /* OBJECT_FORMAT_MACHO */
 530