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 static void
 127 fini_dummy ()
 128 {
 129   asm (FINI_SECTION_ASM_OP);
 130   __do_global_dtors_aux ();
 131 #ifdef FORCE_FINI_SECTION_ALIGN
 132   FORCE_FINI_SECTION_ALIGN;
 133 #endif
 134   asm (TEXT_SECTION_ASM_OP);
 135 }
 136
 137 #else  /* OBJECT_FORMAT_ELF */
 138
 139 /* The function __do_global_ctors_aux is compiled twice (once in crtbegin.o
 140    and once in crtend.o).  It must be declared static to avoid a link
 141    error.  Here, we define __do_global_ctors as an externally callable
 142    function.  It is externally callable so that __main can invoke it when
 143    INVOKE__main is defined.  This has the additional effect of forcing cc1
 144    to switch to the .text section.  */
 145 static void __do_global_ctors_aux ();
 146 void __do_global_ctors ()
 147 {
 148 #ifdef INVOKE__main  /* If __main won't actually call __do_global_ctors
 149                         then it doesn't matter what's inside the function.
 150                         The inside of __do_global_ctors_aux is called
 151                         automatically in that case.
 152                         And the Alliant fx2800 linker crashes
 153                         on this reference.  So prevent the crash.  */
 154   __do_global_ctors_aux ();
 155 #endif
 156 }
 157
 158 asm (INIT_SECTION_ASM_OP);      /* cc1 doesn't know that we are switching! */
 159
 160 /* On some svr4 systems, the initial .init section preamble code provided in
 161    crti.o may do something, such as bump the stack, which we have to
 162    undo before we reach the function prologue code for __do_global_ctors
 163    (directly below).  For such systems, define the macro INIT_SECTION_PREAMBLE
 164    to expand into the code needed to undo the actions of the crti.o file. */
 165
 166 #ifdef INIT_SECTION_PREAMBLE
 167   INIT_SECTION_PREAMBLE;
 168 #endif
 169
 170 /* A routine to invoke all of the global constructors upon entry to the
 171    program.  We put this into the .init section (for systems that have
 172    such a thing) so that we can properly perform the construction of
 173    file-scope static-storage C++ objects within shared libraries.   */
 174
 175 static void
 176 __do_global_ctors_aux ()        /* prologue goes in .init section */
 177 {
 178 #ifdef FORCE_INIT_SECTION_ALIGN
 179   FORCE_INIT_SECTION_ALIGN;     /* Explicit align before switch to .text */
 180 #endif
 181   asm (TEXT_SECTION_ASM_OP);    /* don't put epilogue and body in .init */
 182   DO_GLOBAL_CTORS_BODY;
 183   ON_EXIT (__do_global_dtors, 0);
 184 }
 185
 186 #endif /* OBJECT_FORMAT_ELF */
 187 #endif /* defined(INIT_SECTION_ASM_OP) */
 188
 189 /* Force cc1 to switch to .data section.  */
 190 static func_ptr force_to_data[0] = { };
 191
 192 /* NOTE:  In order to be able to support SVR4 shared libraries, we arrange
 193    to have one set of symbols { __CTOR_LIST__, __DTOR_LIST__, __CTOR_END__,
 194    __DTOR_END__ } per root executable and also one set of these symbols
 195    per shared library.  So in any given whole process image, we may have
 196    multiple definitions of each of these symbols.  In order to prevent
 197    these definitions from conflicting with one another, and in order to
 198    ensure that the proper lists are used for the initialization/finalization
 199    of each individual shared library (respectively), we give these symbols
 200    only internal (i.e. `static') linkage, and we also make it a point to
 201    refer to only the __CTOR_END__ symbol in crtend.o and the __DTOR_LIST__
 202    symbol in crtbegin.o, where they are defined.  */
 203
 204 /* The -1 is a flag to __do_global_[cd]tors
 205    indicating that this table does not start with a count of elements.  */
 206 #ifdef CTOR_LIST_BEGIN
 207 CTOR_LIST_BEGIN;
 208 #else
 209 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 210 STATIC func_ptr __CTOR_LIST__[1] = { (func_ptr) (-1) };
 211 #endif
 212
 213 #ifdef DTOR_LIST_BEGIN
 214 DTOR_LIST_BEGIN;
 215 #else
 216 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 217 STATIC func_ptr __DTOR_LIST__[1] = { (func_ptr) (-1) };
 218 #endif
 219
 220 #endif /* defined(CRT_BEGIN) */
 221
 222 #ifdef CRT_END
 223
 224 #ifdef INIT_SECTION_ASM_OP
 225
 226 #ifdef OBJECT_FORMAT_ELF
 227
 228 static func_ptr __CTOR_END__[];
 229 static void
 230 __do_global_ctors_aux ()
 231 {
 232   func_ptr *p;
 233   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 234     (*p) ();
 235 }
 236
 237 /* Stick a call to __do_global_ctors_aux into the .init section.  */
 238 static void
 239 init_dummy ()
 240 {
 241   asm (INIT_SECTION_ASM_OP);
 242   __do_global_ctors_aux ();
 243 #ifdef FORCE_INIT_SECTION_ALIGN
 244   FORCE_INIT_SECTION_ALIGN;
 245 #endif
 246   asm (TEXT_SECTION_ASM_OP);
 247
 248 /* This is a kludge. The i386 Linux dynamic linker needs ___brk_addr,
 249    __environ and atexit (). We have to make sure they are in the .dynsym
 250    section. We accomplish it by making a dummy call here. This
 251    code is never reached. */
 252
 253 #if defined(__linux__) && defined(__PIC__) && defined(__i386__)
 254   {
 255     extern void *___brk_addr;
 256     extern char **__environ;
 257
 258     ___brk_addr = __environ;
 259     atexit ();
 260   }
 261 #endif
 262 }
 263
 264 #else  /* OBJECT_FORMAT_ELF */
 265
 266 /* Stick the real initialization code, followed by a normal sort of
 267    function epilogue at the very end of the .init section for this
 268    entire root executable file or for this entire shared library file.
 269
 270    Note that we use some tricks here to get *just* the body and just
 271    a function epilogue (but no function prologue) into the .init
 272    section of the crtend.o file.  Specifically, we switch to the .text
 273    section, start to define a function, and then we switch to the .init
 274    section just before the body code.
 275
 276    Earlier on, we put the corresponding function prologue into the .init
 277    section of the crtbegin.o file (which will be linked in first).
 278
 279    Note that we want to invoke all constructors for C++ file-scope static-
 280    storage objects AFTER any other possible initialization actions which
 281    may be performed by the code in the .init section contributions made by
 282    other libraries, etc.  That's because those other initializations may
 283    include setup operations for very primitive things (e.g. initializing
 284    the state of the floating-point coprocessor, etc.) which should be done
 285    before we start to execute any of the user's code. */
 286
 287 static void
 288 __do_global_ctors_aux ()        /* prologue goes in .text section */
 289 {
 290   asm (INIT_SECTION_ASM_OP);
 291   DO_GLOBAL_CTORS_BODY;
 292   ON_EXIT (__do_global_dtors, 0);
 293 }                               /* epilogue and body go in .init section */
 294
 295 #endif /* OBJECT_FORMAT_ELF */
 296
 297 #endif /* defined(INIT_SECTION_ASM_OP) */
 298
 299 /* Force cc1 to switch to .data section.  */
 300 static func_ptr force_to_data[0] = { };
 301
 302 /* Put a word containing zero at the end of each of our two lists of function
 303    addresses.  Note that the words defined here go into the .ctors and .dtors
 304    sections of the crtend.o file, and since that file is always linked in
 305    last, these words naturally end up at the very ends of the two lists
 306    contained in these two sections.  */
 307
 308 #ifdef CTOR_LIST_END
 309 CTOR_LIST_END;
 310 #else
 311 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 312 STATIC func_ptr __CTOR_END__[1] = { (func_ptr) 0 };
 313 #endif
 314
 315 #ifdef DTOR_LIST_END
 316 DTOR_LIST_END;
 317 #else
 318 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 319 STATIC func_ptr __DTOR_END__[1] = { (func_ptr) 0 };
 320 #endif
 321
 322 #endif /* defined(CRT_END) */