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