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 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
  57 /* Provide default definitions for the pseudo-ops used to switch to the
  58    .ctors and .dtors sections.
  59
  60    Note that we want to give these sections the SHF_WRITE attribute
  61    because these sections will actually contain data (i.e. tables of
  62    addresses of functions in the current root executable or shared library
  63    file) and, in the case of a shared library, the relocatable addresses
  64    will have to be properly resolved/relocated (and then written into) by
  65    the dynamic linker when it actually attaches the given shared library
  66    to the executing process.  (Note that on SVR4, you may wish to use the
  67    `-z text' option to the ELF linker, when building a shared library, as
  68    an additional check that you are doing everything right.  But if you do
  69    use the `-z text' option when building a shared library, you will get
  70    errors unless the .ctors and .dtors sections are marked as writable
  71    via the SHF_WRITE attribute.)  */
  72
  73 #ifndef CTORS_SECTION_ASM_OP
  74 #define CTORS_SECTION_ASM_OP    ".section\t.ctors,\"aw\""
  75 #endif
  76 #ifndef DTORS_SECTION_ASM_OP
  77 #define DTORS_SECTION_ASM_OP    ".section\t.dtors,\"aw\""
  78 #endif
  79 #if !defined (EH_FRAME_SECTION_ASM_OP) && defined (DWARF2_UNWIND_INFO) && defined(ASM_OUTPUT_SECTION_NAME)
  80 #define EH_FRAME_SECTION_ASM_OP ".section\t.eh_frame,\"aw\""
  81 #endif
  82
  83 #ifdef OBJECT_FORMAT_ELF
  84
  85 /*  Declare a pointer to void function type.  */
  86 typedef void (*func_ptr) (void);
  87 #define STATIC static
  88
  89 #else  /* OBJECT_FORMAT_ELF */
  90
  91 #include "gbl-ctors.h"
  92
  93 #ifndef ON_EXIT
  94 #define ON_EXIT(a, b)
  95 #endif
  96 #define STATIC
  97
  98 #endif /* OBJECT_FORMAT_ELF */
  99
 100 #ifdef CRT_BEGIN
 101
 102 #ifdef INIT_SECTION_ASM_OP
 103
 104 #ifdef OBJECT_FORMAT_ELF
 105
 106 /* Run all the global destructors on exit from the program.  */
 107
 108 /* Some systems place the number of pointers in the first word of the
 109    table.  On SVR4 however, that word is -1.  In all cases, the table is
 110    null-terminated.  On SVR4, we start from the beginning of the list and
 111    invoke each per-compilation-unit destructor routine in order
 112    until we find that null.
 113
 114    Note that this function MUST be static.  There will be one of these
 115    functions in each root executable and one in each shared library, but
 116    although they all have the same code, each one is unique in that it
 117    refers to one particular associated `__DTOR_LIST__' which belongs to the
 118    same particular root executable or shared library file.
 119
 120    On some systems, this routine is run more than once from the .fini,
 121    when exit is called recursively, so we arrange to remember where in
 122    the list we left off processing, and we resume at that point,
 123    should we be re-invoked.  */
 124
 125 static char __EH_FRAME_BEGIN__[];
 126 static func_ptr __DTOR_LIST__[];
 127 static void
 128 __do_global_dtors_aux ()
 129 {
 130   static func_ptr *p = __DTOR_LIST__ + 1;
 131   static int completed = 0;
 132
 133   if (completed)
 134     return;
 135
 136   while (*p)
 137     {
 138       p++;
 139       (*(p-1)) ();
 140     }
 141
 142 #ifdef EH_FRAME_SECTION_ASM_OP
 143   __deregister_frame (__EH_FRAME_BEGIN__);
 144 #endif
 145   completed = 1;
 146 }
 147
 148
 149 /* Stick a call to __do_global_dtors_aux into the .fini section.  */
 150
 151 static void
 152 fini_dummy ()
 153 {
 154   asm (FINI_SECTION_ASM_OP);
 155   __do_global_dtors_aux ();
 156 #ifdef FORCE_FINI_SECTION_ALIGN
 157   FORCE_FINI_SECTION_ALIGN;
 158 #endif
 159   asm (TEXT_SECTION_ASM_OP);
 160 }
 161
 162 #ifdef EH_FRAME_SECTION_ASM_OP
 163 /* Stick a call to __register_frame into the .init section.  For some reason
 164    calls with no arguments work more reliably in .init, so stick the call
 165    in another function.  */
 166
 167 static void
 168 frame_dummy ()
 169 {
 170   __register_frame (__EH_FRAME_BEGIN__);
 171 }
 172
 173 static void
 174 init_dummy ()
 175 {
 176   asm (INIT_SECTION_ASM_OP);
 177   frame_dummy ();
 178 #ifdef FORCE_INIT_SECTION_ALIGN
 179   FORCE_INIT_SECTION_ALIGN;
 180 #endif
 181   asm (TEXT_SECTION_ASM_OP);
 182 }
 183 #endif /* EH_FRAME_SECTION_ASM_OP */
 184
 185 #else  /* OBJECT_FORMAT_ELF */
 186
 187 /* The function __do_global_ctors_aux is compiled twice (once in crtbegin.o
 188    and once in crtend.o).  It must be declared static to avoid a link
 189    error.  Here, we define __do_global_ctors as an externally callable
 190    function.  It is externally callable so that __main can invoke it when
 191    INVOKE__main is defined.  This has the additional effect of forcing cc1
 192    to switch to the .text section.  */
 193
 194 static void __do_global_ctors_aux ();
 195 void __do_global_ctors ()
 196 {
 197 #ifdef INVOKE__main  /* If __main won't actually call __do_global_ctors
 198                         then it doesn't matter what's inside the function.
 199                         The inside of __do_global_ctors_aux is called
 200                         automatically in that case.
 201                         And the Alliant fx2800 linker crashes
 202                         on this reference.  So prevent the crash.  */
 203   __do_global_ctors_aux ();
 204 #endif
 205 }
 206
 207 asm (INIT_SECTION_ASM_OP);      /* cc1 doesn't know that we are switching! */
 208
 209 /* On some svr4 systems, the initial .init section preamble code provided in
 210    crti.o may do something, such as bump the stack, which we have to
 211    undo before we reach the function prologue code for __do_global_ctors
 212    (directly below).  For such systems, define the macro INIT_SECTION_PREAMBLE
 213    to expand into the code needed to undo the actions of the crti.o file.  */
 214
 215 #ifdef INIT_SECTION_PREAMBLE
 216   INIT_SECTION_PREAMBLE;
 217 #endif
 218
 219 /* A routine to invoke all of the global constructors upon entry to the
 220    program.  We put this into the .init section (for systems that have
 221    such a thing) so that we can properly perform the construction of
 222    file-scope static-storage C++ objects within shared libraries.   */
 223
 224 static void
 225 __do_global_ctors_aux ()        /* prologue goes in .init section */
 226 {
 227 #ifdef FORCE_INIT_SECTION_ALIGN
 228   FORCE_INIT_SECTION_ALIGN;     /* Explicit align before switch to .text */
 229 #endif
 230   asm (TEXT_SECTION_ASM_OP);    /* don't put epilogue and body in .init */
 231   DO_GLOBAL_CTORS_BODY;
 232   ON_EXIT (__do_global_dtors, 0);
 233 }
 234
 235 #endif /* OBJECT_FORMAT_ELF */
 236
 237 #else /* defined(INIT_SECTION_ASM_OP) */
 238
 239 #ifdef HAS_INIT_SECTION
 240 /* This case is used by the Irix 6 port, which supports named sections but
 241    not an SVR4-style .fini section.  __do_global_dtors can be non-static
 242    in this case because we protect it with -hidden_symbol.  */
 243
 244 static char __EH_FRAME_BEGIN__[];
 245 static func_ptr __DTOR_LIST__[];
 246 void
 247 __do_global_dtors ()
 248 {
 249   func_ptr *p;
 250   for (p = __DTOR_LIST__ + 1; *p; p++)
 251     (*p) ();
 252
 253 #ifdef EH_FRAME_SECTION_ASM_OP
 254   __deregister_frame (__EH_FRAME_BEGIN__);
 255 #endif
 256 }
 257 #endif
 258
 259 #endif /* defined(INIT_SECTION_ASM_OP) */
 260
 261 /* Force cc1 to switch to .data section.  */
 262 static func_ptr force_to_data[0] = { };
 263
 264 /* NOTE:  In order to be able to support SVR4 shared libraries, we arrange
 265    to have one set of symbols { __CTOR_LIST__, __DTOR_LIST__, __CTOR_END__,
 266    __DTOR_END__ } per root executable and also one set of these symbols
 267    per shared library.  So in any given whole process image, we may have
 268    multiple definitions of each of these symbols.  In order to prevent
 269    these definitions from conflicting with one another, and in order to
 270    ensure that the proper lists are used for the initialization/finalization
 271    of each individual shared library (respectively), we give these symbols
 272    only internal (i.e. `static') linkage, and we also make it a point to
 273    refer to only the __CTOR_END__ symbol in crtend.o and the __DTOR_LIST__
 274    symbol in crtbegin.o, where they are defined.  */
 275
 276 /* The -1 is a flag to __do_global_[cd]tors
 277    indicating that this table does not start with a count of elements.  */
 278 #ifdef CTOR_LIST_BEGIN
 279 CTOR_LIST_BEGIN;
 280 #else
 281 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 282 STATIC func_ptr __CTOR_LIST__[1] = { (func_ptr) (-1) };
 283 #endif
 284
 285 #ifdef DTOR_LIST_BEGIN
 286 DTOR_LIST_BEGIN;
 287 #else
 288 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 289 STATIC func_ptr __DTOR_LIST__[1] = { (func_ptr) (-1) };
 290 #endif
 291
 292 #ifdef EH_FRAME_SECTION_ASM_OP
 293 /* Stick a label at the beginning of the frame unwind info so we can register
 294    and deregister it with the exception handling library code.  */
 295
 296 asm (EH_FRAME_SECTION_ASM_OP);
 297 #ifdef INIT_SECTION_ASM_OP
 298 STATIC
 299 #endif
 300 char __EH_FRAME_BEGIN__[] = { };
 301 #endif /* EH_FRAME_SECTION_ASM_OP */
 302
 303 #endif /* defined(CRT_BEGIN) */
 304
 305 #ifdef CRT_END
 306
 307 #ifdef INIT_SECTION_ASM_OP
 308
 309 #ifdef OBJECT_FORMAT_ELF
 310
 311 static func_ptr __CTOR_END__[];
 312 static void
 313 __do_global_ctors_aux ()
 314 {
 315   func_ptr *p;
 316   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 317     (*p) ();
 318 }
 319
 320 /* Stick a call to __do_global_ctors_aux into the .init section.  */
 321
 322 static void
 323 init_dummy ()
 324 {
 325   asm (INIT_SECTION_ASM_OP);
 326   __do_global_ctors_aux ();
 327 #ifdef FORCE_INIT_SECTION_ALIGN
 328   FORCE_INIT_SECTION_ALIGN;
 329 #endif
 330   asm (TEXT_SECTION_ASM_OP);
 331
 332 /* This is a kludge. The i386 Linux dynamic linker needs ___brk_addr,
 333    __environ and atexit (). We have to make sure they are in the .dynsym
 334    section. We accomplish it by making a dummy call here. This
 335    code is never reached.  */
 336
 337 #if defined(__linux__) && defined(__PIC__) && defined(__i386__)
 338   {
 339     extern void *___brk_addr;
 340     extern char **__environ;
 341
 342     ___brk_addr = __environ;
 343     atexit ();
 344   }
 345 #endif
 346 }
 347
 348 #else  /* OBJECT_FORMAT_ELF */
 349
 350 /* Stick the real initialization code, followed by a normal sort of
 351    function epilogue at the very end of the .init section for this
 352    entire root executable file or for this entire shared library file.
 353
 354    Note that we use some tricks here to get *just* the body and just
 355    a function epilogue (but no function prologue) into the .init
 356    section of the crtend.o file.  Specifically, we switch to the .text
 357    section, start to define a function, and then we switch to the .init
 358    section just before the body code.
 359
 360    Earlier on, we put the corresponding function prologue into the .init
 361    section of the crtbegin.o file (which will be linked in first).
 362
 363    Note that we want to invoke all constructors for C++ file-scope static-
 364    storage objects AFTER any other possible initialization actions which
 365    may be performed by the code in the .init section contributions made by
 366    other libraries, etc.  That's because those other initializations may
 367    include setup operations for very primitive things (e.g. initializing
 368    the state of the floating-point coprocessor, etc.) which should be done
 369    before we start to execute any of the user's code.  */
 370
 371 static void
 372 __do_global_ctors_aux ()        /* prologue goes in .text section */
 373 {
 374   asm (INIT_SECTION_ASM_OP);
 375   DO_GLOBAL_CTORS_BODY;
 376   ON_EXIT (__do_global_dtors, 0);
 377 }                               /* epilogue and body go in .init section */
 378
 379 #endif /* OBJECT_FORMAT_ELF */
 380
 381 #else /* defined(INIT_SECTION_ASM_OP) */
 382
 383 #ifdef HAS_INIT_SECTION
 384 /* This case is used by the Irix 6 port, which supports named sections but
 385    not an SVR4-style .init section.  __do_global_ctors can be non-static
 386    in this case because we protect it with -hidden_symbol.  */
 387 extern char __EH_FRAME_BEGIN__[];
 388 static func_ptr __CTOR_END__[];
 389 void
 390 __do_global_ctors ()
 391 {
 392   func_ptr *p;
 393 #ifdef EH_FRAME_SECTION_ASM_OP
 394   __register_frame (__EH_FRAME_BEGIN__);
 395 #endif
 396   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 397     (*p) ();
 398 }
 399 #endif
 400
 401 #endif /* defined(INIT_SECTION_ASM_OP) */
 402
 403 /* Force cc1 to switch to .data section.  */
 404 static func_ptr force_to_data[0] = { };
 405
 406 /* Put a word containing zero at the end of each of our two lists of function
 407    addresses.  Note that the words defined here go into the .ctors and .dtors
 408    sections of the crtend.o file, and since that file is always linked in
 409    last, these words naturally end up at the very ends of the two lists
 410    contained in these two sections.  */
 411
 412 #ifdef CTOR_LIST_END
 413 CTOR_LIST_END;
 414 #else
 415 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 416 STATIC func_ptr __CTOR_END__[1] = { (func_ptr) 0 };
 417 #endif
 418
 419 #ifdef DTOR_LIST_END
 420 DTOR_LIST_END;
 421 #else
 422 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 423 STATIC func_ptr __DTOR_END__[1] = { (func_ptr) 0 };
 424 #endif
 425
 426 #ifdef EH_FRAME_SECTION_ASM_OP
 427 /* Terminate the frame unwind info section with a 4byte 0 as a sentinel;
 428    this would be the 'length' field in a real FDE.  */
 429
 430 typedef unsigned int ui32 __attribute__ ((mode (SI)));
 431 asm (EH_FRAME_SECTION_ASM_OP);
 432 STATIC ui32 __FRAME_END__[] = { 0 };
 433 #endif /* EH_FRAME_SECTION */
 434
 435 #endif /* defined(CRT_END) */