gcc/crtstuff.c

   1 /* Specialized bits of code needed to support construction and
   2    destruction of file-scope objects in C++ code.
   3
   4    Written by Ron Guilmette (rfg@netcom.com) with help from Richard Stallman.
   5
   6 Copyright (C) 1991, 1994 Free Software Foundation, Inc.
   7
   8 This file is part of GNU CC.
   9
  10 GNU CC is free software; you can redistribute it and/or modify
  11 it under the terms of the GNU General Public License as published by
  12 the Free Software Foundation; either version 2, or (at your option)
  13 any later version.
  14
  15 GNU CC is distributed in the hope that it will be useful,
  16 but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 GNU General Public License for more details.
  19
  20 You should have received a copy of the GNU General Public License
  21 along with GNU CC; see the file COPYING.  If not, write to
  22 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
  23
  24 /* As a special exception, if you link this library with files
  25    compiled with GCC to produce an executable, this does not cause
  26    the resulting executable to be covered by the GNU General Public License.
  27    This exception does not however invalidate any other reasons why
  28    the executable file might be covered by the GNU General Public License.  */
  29
  30 /* This file is a bit like libgcc1.c/libgcc2.c in that it is compiled
  31    multiple times and yields multiple .o files.
  32
  33    This file is useful on target machines where the object file format
  34    supports multiple "user-defined" sections (e.g. COFF, ELF, ROSE).  On
  35    such systems, this file allows us to avoid running collect (or any
  36    other such slow and painful kludge).  Additionally, if the target
  37    system supports a .init section, this file allows us to support the
  38    linking of C++ code with a non-C++ main program.
  39
  40    Note that if INIT_SECTION_ASM_OP is defined in the tm.h file, then
  41    this file *will* make use of the .init section.  If that symbol is
  42    not defined however, then the .init section will not be used.
  43
  44    Currently, only ELF and COFF are supported.  It is likely however that
  45    ROSE could also be supported, if someone was willing to do the work to
  46    make whatever (small?) adaptations are needed.  (Some work may be
  47    needed on the ROSE assembler and linker also.)
  48
  49    This file must be compiled with gcc.  */
  50
  51 /* It is incorrect to include config.h here, because this file is being
  52    compiled for the target, and hence definitions concerning only the host
  53    do not apply.  */
  54
  55 #include "tm.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
  80 #ifdef OBJECT_FORMAT_ELF
  81
  82 /*  Declare a pointer to void function type.  */
  83 typedef void (*func_ptr) (void);
  84 #define STATIC static
  85
  86 #else  /* OBJECT_FORMAT_ELF */
  87
  88 #include "gbl-ctors.h"
  89
  90 #ifndef ON_EXIT
  91 #define ON_EXIT(a, b)
  92 #endif
  93 #define STATIC
  94
  95 #endif /* OBJECT_FORMAT_ELF */
  96
  97 #ifdef CRT_BEGIN
  98
  99 #ifdef INIT_SECTION_ASM_OP
 100
 101 #ifdef OBJECT_FORMAT_ELF
 102
 103 /* Run all the global destructors on exit from the program.  */
 104
 105 /* Some systems place the number of pointers in the first word of the
 106    table.  On SVR4 however, that word is -1.  In all cases, the table is
 107    null-terminated.  On SVR4, we start from the beginning of the list and
 108    invoke each per-compilation-unit destructor routine in order
 109    until we find that null.
 110
 111    Note that this function MUST be static.  There will be one of these
 112    functions in each root executable and one in each shared library, but
 113    although they all have the same code, each one is unique in that it
 114    refers to one particular associated `__DTOR_LIST__' which belongs to the
 115    same particular root executable or shared library file.  */
 116
 117 static func_ptr __DTOR_LIST__[];
 118 static void
 119 __do_global_dtors_aux ()
 120 {
 121   func_ptr *p;
 122   for (p = __DTOR_LIST__ + 1; *p; p++)
 123     (*p) ();
 124 }
 125
 126 /* Stick a call to __do_global_dtors_aux into the .fini section.  */
 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 static void __do_global_ctors_aux ();
 147 void __do_global_ctors ()
 148 {
 149 #ifdef INVOKE__main  /* If __main won't actually call __do_global_ctors
 150                         then it doesn't matter what's inside the function.
 151                         The inside of __do_global_ctors_aux is called
 152                         automatically in that case.
 153                         And the Alliant fx2800 linker crashes
 154                         on this reference.  So prevent the crash.  */
 155   __do_global_ctors_aux ();
 156 #endif
 157 }
 158
 159 asm (INIT_SECTION_ASM_OP);      /* cc1 doesn't know that we are switching! */
 160
 161 /* A routine to invoke all of the global constructors upon entry to the
 162    program.  We put this into the .init section (for systems that have
 163    such a thing) so that we can properly perform the construction of
 164    file-scope static-storage C++ objects within shared libraries.   */
 165
 166 static void
 167 __do_global_ctors_aux ()        /* prologue goes in .init section */
 168 {
 169 #ifdef FORCE_INIT_SECTION_ALIGN
 170   FORCE_INIT_SECTION_ALIGN;     /* Explicit align before switch to .text */
 171 #endif
 172   asm (TEXT_SECTION_ASM_OP);    /* don't put epilogue and body in .init */
 173   DO_GLOBAL_CTORS_BODY;
 174   ON_EXIT (__do_global_dtors, 0);
 175 }
 176
 177 #endif /* OBJECT_FORMAT_ELF */
 178 #endif /* defined(INIT_SECTION_ASM_OP) */
 179
 180 /* Force cc1 to switch to .data section.  */
 181 static func_ptr force_to_data[0] = { };
 182
 183 /* NOTE:  In order to be able to support SVR4 shared libraries, we arrange
 184    to have one set of symbols { __CTOR_LIST__, __DTOR_LIST__, __CTOR_END__,
 185    __DTOR_END__ } per root executable and also one set of these symbols
 186    per shared library.  So in any given whole process image, we may have
 187    multiple definitions of each of these symbols.  In order to prevent
 188    these definitions from conflicting with one another, and in order to
 189    ensure that the proper lists are used for the initialization/finalization
 190    of each individual shared library (respectively), we give these symbols
 191    only internal (i.e. `static') linkage, and we also make it a point to
 192    refer to only the __CTOR_END__ symbol in crtend.o and the __DTOR_LIST__
 193    symbol in crtbegin.o, where they are defined.  */
 194
 195 /* The -1 is a flag to __do_global_[cd]tors
 196    indicating that this table does not start with a count of elements.  */
 197 #ifdef CTOR_LIST_BEGIN
 198 CTOR_LIST_BEGIN;
 199 #else
 200 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 201 STATIC func_ptr __CTOR_LIST__[1] = { (func_ptr) (-1) };
 202 #endif
 203
 204 #ifdef DTOR_LIST_BEGIN
 205 DTOR_LIST_BEGIN;
 206 #else
 207 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 208 STATIC func_ptr __DTOR_LIST__[1] = { (func_ptr) (-1) };
 209 #endif
 210
 211 #endif /* defined(CRT_BEGIN) */
 212
 213 #ifdef CRT_END
 214
 215 #ifdef INIT_SECTION_ASM_OP
 216
 217 #ifdef OBJECT_FORMAT_ELF
 218
 219 static func_ptr __CTOR_END__[];
 220 static void
 221 __do_global_ctors_aux ()
 222 {
 223   func_ptr *p;
 224   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 225     (*p) ();
 226 }
 227
 228 /* Stick a call to __do_global_ctors_aux into the .init section.  */
 229 static void
 230 init_dummy ()
 231 {
 232   asm (INIT_SECTION_ASM_OP);
 233   __do_global_ctors_aux ();
 234 #ifdef FORCE_INIT_SECTION_ALIGN
 235   FORCE_INIT_SECTION_ALIGN;
 236 #endif
 237   asm (TEXT_SECTION_ASM_OP);
 238
 239 /* This is a kludge. The Linux dynamic linker needs  ___brk_addr, __environ
 240    and atexit (). We have to make sure they are in the .dynsym section. We
 241    accomplish it by making a dummy call here. This
 242    code is never reached. */
 243
 244 #if defined(__linux__) && defined(__PIC__)
 245   {
 246     extern void *___brk_addr;
 247     extern char **__environ;
 248
 249     ___brk_addr = __environ;
 250     atexit ();
 251   }
 252 #endif
 253 }
 254
 255 #else  /* OBJECT_FORMAT_ELF */
 256
 257 /* Stick the real initialization code, followed by a normal sort of
 258    function epilogue at the very end of the .init section for this
 259    entire root executable file or for this entire shared library file.
 260
 261    Note that we use some tricks here to get *just* the body and just
 262    a function epilogue (but no function prologue) into the .init
 263    section of the crtend.o file.  Sepcifically, we switch to the .text
 264    section, start to define a function, and then we switch to the .init
 265    section just before the body code.
 266
 267    Earlier on, we put the corresponding function prologue into the .init
 268    section of the crtbegin.o file (which will be linked in first).
 269
 270    Note that we want to invoke all constructors for C++ file-scope static-
 271    storage objects AFTER any other possible initialization actions which
 272    may be performed by the code in the .init section contributions made by
 273    other libraries, etc.  That's because those other initializations may
 274    include setup operations for very primitive things (e.g. initializing
 275    the state of the floating-point coprocessor, etc.) which should be done
 276    before we start to execute any of the user's code. */
 277
 278 static void
 279 __do_global_ctors_aux ()        /* prologue goes in .text section */
 280 {
 281   asm (INIT_SECTION_ASM_OP);
 282   DO_GLOBAL_CTORS_BODY;
 283   ON_EXIT (__do_global_dtors, 0);
 284 }                               /* epilogue and body go in .init section */
 285
 286 #endif /* OBJECT_FORMAT_ELF */
 287
 288 #endif /* defined(INIT_SECTION_ASM_OP) */
 289
 290 /* Force cc1 to switch to .data section.  */
 291 static func_ptr force_to_data[0] = { };
 292
 293 /* Put a word containing zero at the end of each of our two lists of function
 294    addresses.  Note that the words defined here go into the .ctors and .dtors
 295    sections of the crtend.o file, and since that file is always linked in
 296    last, these words naturally end up at the very ends of the two lists
 297    contained in these two sections.  */
 298
 299 #ifdef CTOR_LIST_END
 300 CTOR_LIST_END;
 301 #else
 302 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 303 STATIC func_ptr __CTOR_END__[1] = { (func_ptr) 0 };
 304 #endif
 305
 306 #ifdef DTOR_LIST_END
 307 DTOR_LIST_END;
 308 #else
 309 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 310 STATIC func_ptr __DTOR_END__[1] = { (func_ptr) 0 };
 311 #endif
 312
 313 #endif /* defined(CRT_END) */