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