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, 1995 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, 59 Temple Place - Suite 330,
  23 Boston, MA 02111-1307, USA.  */
  24
  25 /* As a special exception, if you link this library with files
  26    compiled with GCC to produce an executable, this does not cause
  27    the resulting executable to be covered by the GNU General Public License.
  28    This exception does not however invalidate any other reasons why
  29    the executable file might be covered by the GNU General Public License.  */
  30
  31 /* This file is a bit like libgcc1.c/libgcc2.c in that it is compiled
  32    multiple times and yields multiple .o files.
  33
  34    This file is useful on target machines where the object file format
  35    supports multiple "user-defined" sections (e.g. COFF, ELF, ROSE).  On
  36    such systems, this file allows us to avoid running collect (or any
  37    other such slow and painful kludge).  Additionally, if the target
  38    system supports a .init section, this file allows us to support the
  39    linking of C++ code with a non-C++ main program.
  40
  41    Note that if INIT_SECTION_ASM_OP is defined in the tm.h file, then
  42    this file *will* make use of the .init section.  If that symbol is
  43    not defined however, then the .init section will not be used.
  44
  45    Currently, only ELF and COFF are supported.  It is likely however that
  46    ROSE could also be supported, if someone was willing to do the work to
  47    make whatever (small?) adaptations are needed.  (Some work may be
  48    needed on the ROSE assembler and linker also.)
  49
  50    This file must be compiled with gcc.  */
  51
  52 /* It is incorrect to include config.h here, because this file is being
  53    compiled for the target, and hence definitions concerning only the host
  54    do not apply.  */
  55
  56 #include "tm.h"
  57
  58 /* Provide default definitions for the pseudo-ops used to switch to the
  59    .ctors and .dtors sections.
  60
  61    Note that we want to give these sections the SHF_WRITE attribute
  62    because these sections will actually contain data (i.e. tables of
  63    addresses of functions in the current root executable or shared library
  64    file) and, in the case of a shared library, the relocatable addresses
  65    will have to be properly resolved/relocated (and then written into) by
  66    the dynamic linker when it actually attaches the given shared library
  67    to the executing process.  (Note that on SVR4, you may wish to use the
  68    `-z text' option to the ELF linker, when building a shared library, as
  69    an additional check that you are doing everything right.  But if you do
  70    use the `-z text' option when building a shared library, you will get
  71    errors unless the .ctors and .dtors sections are marked as writable
  72    via the SHF_WRITE attribute.)  */
  73
  74 #ifndef CTORS_SECTION_ASM_OP
  75 #define CTORS_SECTION_ASM_OP    ".section\t.ctors,\"aw\""
  76 #endif
  77 #ifndef DTORS_SECTION_ASM_OP
  78 #define DTORS_SECTION_ASM_OP    ".section\t.dtors,\"aw\""
  79 #endif
  80
  81 #ifdef OBJECT_FORMAT_ELF
  82
  83 /*  Declare a pointer to void function type.  */
  84 typedef void (*func_ptr) (void);
  85 #define STATIC static
  86
  87 #else  /* OBJECT_FORMAT_ELF */
  88
  89 #include "gbl-ctors.h"
  90
  91 #ifndef ON_EXIT
  92 #define ON_EXIT(a, b)
  93 #endif
  94 #define STATIC
  95
  96 #endif /* OBJECT_FORMAT_ELF */
  97
  98 #ifdef CRT_BEGIN
  99
 100 #ifdef INIT_SECTION_ASM_OP
 101
 102 #ifdef OBJECT_FORMAT_ELF
 103
 104 /* Run all the global destructors on exit from the program.  */
 105
 106 /* Some systems place the number of pointers in the first word of the
 107    table.  On SVR4 however, that word is -1.  In all cases, the table is
 108    null-terminated.  On SVR4, we start from the beginning of the list and
 109    invoke each per-compilation-unit destructor routine in order
 110    until we find that null.
 111
 112    Note that this function MUST be static.  There will be one of these
 113    functions in each root executable and one in each shared library, but
 114    although they all have the same code, each one is unique in that it
 115    refers to one particular associated `__DTOR_LIST__' which belongs to the
 116    same particular root executable or shared library file.  */
 117
 118 static func_ptr __DTOR_LIST__[];
 119 static void
 120 __do_global_dtors_aux ()
 121 {
 122   func_ptr *p;
 123   for (p = __DTOR_LIST__ + 1; *p; p++)
 124     (*p) ();
 125 }
 126
 127 /* Stick a call to __do_global_dtors_aux into the .fini section.  */
 128 static void
 129 fini_dummy ()
 130 {
 131   asm (FINI_SECTION_ASM_OP);
 132   __do_global_dtors_aux ();
 133 #ifdef FORCE_FINI_SECTION_ALIGN
 134   FORCE_FINI_SECTION_ALIGN;
 135 #endif
 136   asm (TEXT_SECTION_ASM_OP);
 137 }
 138
 139 #else  /* OBJECT_FORMAT_ELF */
 140
 141 /* The function __do_global_ctors_aux is compiled twice (once in crtbegin.o
 142    and once in crtend.o).  It must be declared static to avoid a link
 143    error.  Here, we define __do_global_ctors as an externally callable
 144    function.  It is externally callable so that __main can invoke it when
 145    INVOKE__main is defined.  This has the additional effect of forcing cc1
 146    to switch to the .text section.  */
 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 #endif /* defined(INIT_SECTION_ASM_OP) */
 190
 191 /* Force cc1 to switch to .data section.  */
 192 static func_ptr force_to_data[0] = { };
 193
 194 /* NOTE:  In order to be able to support SVR4 shared libraries, we arrange
 195    to have one set of symbols { __CTOR_LIST__, __DTOR_LIST__, __CTOR_END__,
 196    __DTOR_END__ } per root executable and also one set of these symbols
 197    per shared library.  So in any given whole process image, we may have
 198    multiple definitions of each of these symbols.  In order to prevent
 199    these definitions from conflicting with one another, and in order to
 200    ensure that the proper lists are used for the initialization/finalization
 201    of each individual shared library (respectively), we give these symbols
 202    only internal (i.e. `static') linkage, and we also make it a point to
 203    refer to only the __CTOR_END__ symbol in crtend.o and the __DTOR_LIST__
 204    symbol in crtbegin.o, where they are defined.  */
 205
 206 /* The -1 is a flag to __do_global_[cd]tors
 207    indicating that this table does not start with a count of elements.  */
 208 #ifdef CTOR_LIST_BEGIN
 209 CTOR_LIST_BEGIN;
 210 #else
 211 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 212 STATIC func_ptr __CTOR_LIST__[1] = { (func_ptr) (-1) };
 213 #endif
 214
 215 #ifdef DTOR_LIST_BEGIN
 216 DTOR_LIST_BEGIN;
 217 #else
 218 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 219 STATIC func_ptr __DTOR_LIST__[1] = { (func_ptr) (-1) };
 220 #endif
 221
 222 #endif /* defined(CRT_BEGIN) */
 223
 224 #ifdef CRT_END
 225
 226 #ifdef INIT_SECTION_ASM_OP
 227
 228 #ifdef OBJECT_FORMAT_ELF
 229
 230 static func_ptr __CTOR_END__[];
 231 static void
 232 __do_global_ctors_aux ()
 233 {
 234   func_ptr *p;
 235   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
 236     (*p) ();
 237 }
 238
 239 /* Stick a call to __do_global_ctors_aux into the .init section.  */
 240 static void
 241 init_dummy ()
 242 {
 243   asm (INIT_SECTION_ASM_OP);
 244   __do_global_ctors_aux ();
 245 #ifdef FORCE_INIT_SECTION_ALIGN
 246   FORCE_INIT_SECTION_ALIGN;
 247 #endif
 248   asm (TEXT_SECTION_ASM_OP);
 249
 250 /* This is a kludge. The Linux dynamic linker needs  ___brk_addr, __environ
 251    and atexit (). We have to make sure they are in the .dynsym section. We
 252    accomplish it by making a dummy call here. This
 253    code is never reached. */
 254
 255 #if defined(__linux__) && defined(__PIC__)
 256   {
 257     extern void *___brk_addr;
 258     extern char **__environ;
 259
 260     ___brk_addr = __environ;
 261     atexit ();
 262   }
 263 #endif
 264 }
 265
 266 #else  /* OBJECT_FORMAT_ELF */
 267
 268 /* Stick the real initialization code, followed by a normal sort of
 269    function epilogue at the very end of the .init section for this
 270    entire root executable file or for this entire shared library file.
 271
 272    Note that we use some tricks here to get *just* the body and just
 273    a function epilogue (but no function prologue) into the .init
 274    section of the crtend.o file.  Specifically, we switch to the .text
 275    section, start to define a function, and then we switch to the .init
 276    section just before the body code.
 277
 278    Earlier on, we put the corresponding function prologue into the .init
 279    section of the crtbegin.o file (which will be linked in first).
 280
 281    Note that we want to invoke all constructors for C++ file-scope static-
 282    storage objects AFTER any other possible initialization actions which
 283    may be performed by the code in the .init section contributions made by
 284    other libraries, etc.  That's because those other initializations may
 285    include setup operations for very primitive things (e.g. initializing
 286    the state of the floating-point coprocessor, etc.) which should be done
 287    before we start to execute any of the user's code. */
 288
 289 static void
 290 __do_global_ctors_aux ()        /* prologue goes in .text section */
 291 {
 292   asm (INIT_SECTION_ASM_OP);
 293   DO_GLOBAL_CTORS_BODY;
 294   ON_EXIT (__do_global_dtors, 0);
 295 }                               /* epilogue and body go in .init section */
 296
 297 #endif /* OBJECT_FORMAT_ELF */
 298
 299 #endif /* defined(INIT_SECTION_ASM_OP) */
 300
 301 /* Force cc1 to switch to .data section.  */
 302 static func_ptr force_to_data[0] = { };
 303
 304 /* Put a word containing zero at the end of each of our two lists of function
 305    addresses.  Note that the words defined here go into the .ctors and .dtors
 306    sections of the crtend.o file, and since that file is always linked in
 307    last, these words naturally end up at the very ends of the two lists
 308    contained in these two sections.  */
 309
 310 #ifdef CTOR_LIST_END
 311 CTOR_LIST_END;
 312 #else
 313 asm (CTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 314 STATIC func_ptr __CTOR_END__[1] = { (func_ptr) 0 };
 315 #endif
 316
 317 #ifdef DTOR_LIST_END
 318 DTOR_LIST_END;
 319 #else
 320 asm (DTORS_SECTION_ASM_OP);     /* cc1 doesn't know that we are switching! */
 321 STATIC func_ptr __DTOR_END__[1] = { (func_ptr) 0 };
 322 #endif
 323
 324 #endif /* defined(CRT_END) */