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