start.s

Glibc 2.3.2源代码(解压后有100多M)

/* Startup code compliant to the ELF i386 ABI.
   Copyright (C) 1995,1996,1997,1998,2000,2001, 2002 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.  */

/* This is the canonical entry point, usually the first thing in the text
   segment.  The SVR4/i386 ABI (pages 3-31, 3-32) says that when the entry
   point runs, most registers' values are unspecified, except for:

   %edx		Contains a function pointer to be registered with `atexit'.
		This is how the dynamic linker arranges to have DT_FINI
		functions called for shared libraries that have been loaded
		before this code runs.

   %esp		The stack contains the arguments and environment:
		0(%esp)			argc
		4(%esp)			argv[0]
		...
		(4*argc)(%esp)		NULL
		(4*(argc+1))(%esp)	envp[0]
		...
					NULL
*/

#include "bp-sym.h"

	.text
	.globl _start
	.type _start,@function
_start:
	/* Clear the frame pointer.  The ABI suggests this be done, to mark
	   the outermost frame obviously.  */
	xorl %ebp, %ebp

	/* Extract the arguments as encoded on the stack and set up
	   the arguments for `main': argc, argv.  envp will be determined
	   later in __libc_start_main.  */
	popl %esi		/* Pop the argument count.  */
	movl %esp, %ecx		/* argv starts just at the current stack top.*/

	/* Before pushing the arguments align the stack to a 16-byte
	(SSE needs 16-byte alignment) boundary to avoid penalties from
	misaligned accesses.  Thanks to Edward Seidl <[e-mail]>
	for pointing this out.  */
	andl $0xfffffff0, %esp
	pushl %eax		/* Push garbage because we allocate
				   28 more bytes.  */

	/* Provide the highest stack address to the user code (for stacks
	   which grow downwards).  */
	pushl %esp

	pushl %edx		/* Push address of the shared library
				   termination function.  */

	/* Push address of our own entry points to .fini and .init.  */
	pushl $__libc_csu_fini
	pushl $__libc_csu_init

	pushl %ecx		/* Push second argument: argv.  */
	pushl %esi		/* Push first argument: argc.  */

	pushl $BP_SYM (main)

	/* Call the user's main function, and exit with its value.
	   But let the libc call main.    */
	call BP_SYM (__libc_start_main)

	hlt			/* Crash if somehow `exit' does return.  */

/* To fulfill the System V/i386 ABI we need this symbol.  Yuck, it's so
   meaningless since we don't support machines < 80386.  */
	.section .rodata
	.globl _fp_hw
_fp_hw:	.long 3
	.size _fp_hw, 4
	.type _fp_hw,@object

/* Define a symbol for the first piece of initialized data.  */
	.data
	.globl __data_start
__data_start:
	.long 0
	.weak data_start
	data_start = __data_start