start.c

Glibc 2.3.2源代码(解压后有100多M)

/* Copyright (C) 1991, 92, 93, 94, 95, 96, 97 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>

#ifndef NO_SHLIB
#include <sys/exec.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <link.h>
#include <syscall.h>
#endif

#if !defined (__GNUC__) || __GNUC__ < 2
  #error This file uses GNU C extensions; you must compile with GCC version 2.
#endif

/* The first piece of initialized data.  */
int __data_start = 0;
#ifdef HAVE_WEAK_SYMBOLS
weak_alias (__data_start, data_start)
#endif

extern void __libc_init __P ((int argc, char **argv, char **envp));
extern int main __P ((int argc, char **argv, char **envp));

register long int sp asm("%sp"), fp asm("%fp");

#ifndef NO_SHLIB
static void init_shlib __P ((void));
#endif

#ifndef NO_EXPLICIT_START
/* Declare _start with an explicit assembly symbol name of `start'
   (note no leading underscore).  This is the name Sun's crt0.o uses,
   and programs are often linked with `ld -e start'.  */
void _start (void) asm ("start");
#endif

void
_start (void)
{
  /* It is important that these be declared `register'.
     Otherwise, when compiled without optimization, they are put on the
     stack, which loses completely after we zero the FP.  */
  register int argc;
  register char **argv, **envp;

  /* Unwind the frame built when we entered the function.  */
  asm("restore");

  /* And clear the frame pointer.  */
  fp = 0;

  /* The argument info starts after one register
     window (64 bytes) past the SP.  */
  argc = ((int *) sp)[16];
  argv = (char **) &((int *) sp)[17];
  envp = &argv[argc + 1];
  __environ = envp;

#ifndef NO_SHLIB
  init_shlib ();
#endif

  /* Allocate 24 bytes of stack space for the register save area.  */
  sp -= 24;
  __libc_init (argc, argv, envp);

  exit (main (argc, argv, envp));
}

#ifndef NO_SHLIB

/* System calls for use by the bootstrap routine.
   These are defined here since the usual calls may be dynamically linked.  */

int syscall (int sysno, ...) asm ("init_syscall");
asm ("init_syscall:\n"
     "	clr %g1\n"
     "	ta 0\n"
     "	bcc 1f\n"
     "	sethi %hi(_errno), %g1\n"
     "	st %o0, [%g1 + %lo(_errno)]\n"
     "	sub %g0, 1, %o0\n"
     "1:retl\n"
     "	nop");

static void
init_shlib ()
{
  extern struct link_dynamic _DYNAMIC;
  int so, zf;
  caddr_t somap;
  caddr_t sodmap;
  caddr_t sobssmap;
  void (*ldstart) (int, int);
  struct exec soexec;
  struct
    {
      caddr_t crt_ba;
      int crt_dzfd;
      int crt_ldfd;
      struct link_dynamic *crt_dp;
      char **crt_ep;
      caddr_t crt_bp;
    } soarg;

  /* If not dynamically linked, do nothing.  */
  if (&_DYNAMIC == 0)
    return;

  /* Map in the dynamic linker.  */
  so = syscall (SYS_open, "/usr/lib/ld.so", O_RDONLY);
  if (syscall (SYS_read, so, &soexec, sizeof (soexec)) != sizeof (soexec)
      || soexec.a_magic != ZMAGIC)
    {
      static const char emsg[] = "crt0: no /usr/lib/ld.so\n";

      syscall (SYS_write, 2, emsg, sizeof (emsg) - 1);
      syscall (SYS_exit, 127);
    }
  somap = (caddr_t) syscall (SYS_mmap, 0,
			     soexec.a_text + soexec.a_data + soexec.a_bss,
			     PROT_READ | PROT_EXEC, _MAP_NEW | MAP_PRIVATE,
			     so, 0);
  sodmap = (caddr_t) syscall (SYS_mmap, somap + soexec.a_text, soexec.a_data,
			      PROT_READ | PROT_WRITE | PROT_EXEC,
			      _MAP_NEW | MAP_FIXED | MAP_PRIVATE,
			      so, soexec.a_text);
  zf = syscall (SYS_open, "/dev/zero", O_RDONLY);
  if (soexec.a_bss != 0)
    sobssmap = (caddr_t) syscall (SYS_mmap,
				  somap + soexec.a_text + soexec.a_data,
				  soexec.a_bss,
				  PROT_READ | PROT_WRITE | PROT_EXEC,
				  _MAP_NEW | MAP_FIXED | MAP_PRIVATE,
				  zf, 0);

  /* Call the entry point of the dynamic linker.  */
  soarg.crt_ba = somap;
  soarg.crt_dzfd = zf;
  soarg.crt_ldfd = so;
  soarg.crt_dp = &_DYNAMIC;
  soarg.crt_ep = __environ;
  soarg.crt_bp = (caddr_t) &&retaddr;

  ldstart = (__typeof (ldstart)) (somap + soexec.a_entry);
  (*ldstart) (1, (char *) &soarg - (char *) sp);

 retaddr:
}

#endif