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