aboutsummaryrefslogtreecommitdiff
path: root/sysdeps/i386/elf/start.S
blob: 95f74ed647e8cb55fd5252bfb8f7d2f9e82a2dbb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
/* Startup code compliant to the ELF i386 ABI.
   Copyright (C) 1995, 1996, 1997, 1998 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 Library General Public License as
   published by the Free Software Foundation; either version 2 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  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
*/

	.text
	.globl _start
_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 double word
	   boundary to avoid penalties from misaligned accesses.  Thanks
	   to Edward Seidl <seidl@janed.com> for pointing this out.  */
	andl $0xfffffff8, %esp
	pushl %edx		/* Push address of the shared library
				   termination function.  */

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

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

	pushl $main

	/* Call the user's main function, and exit with its value.
	   But let the libc call main.    */
	call __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
	.long 3
	.size _fp_hw, 4

/* 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