1 /* Startup code compliant to the ELF i386 ABI.
2 Copyright (C) 1995-1998,2000,2001,2002,2003 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, write to the Free
17 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
20 /* This is the canonical entry point, usually the first thing in the text
21 segment. The SVR4/i386 ABI (pages 3-31, 3-32) says that when the entry
22 point runs, most registers' values are unspecified, except for:
24 %edx Contains a function pointer to be registered with `atexit'.
25 This is how the dynamic linker arranges to have DT_FINI
26 functions called for shared libraries that have been loaded
27 before this code runs.
29 %esp The stack contains the arguments and environment:
34 (4*(argc+1))(%esp) envp[0]
43 .type _start,@function
45 /* Clear the frame pointer. The ABI suggests this be done, to mark
46 the outermost frame obviously. */
49 /* Extract the arguments as encoded on the stack and set up
50 the arguments for `main': argc, argv. envp will be determined
51 later in __libc_start_main. */
52 popl %esi /* Pop the argument count. */
53 movl %esp, %ecx /* argv starts just at the current stack top.*/
55 /* Before pushing the arguments align the stack to a 16-byte
56 (SSE needs 16-byte alignment) boundary to avoid penalties from
57 misaligned accesses. Thanks to Edward Seidl <seidl@janed.com>
58 for pointing this out. */
59 andl $0xfffffff0, %esp
60 pushl %eax /* Push garbage because we allocate
63 /* Provide the highest stack address to the user code (for stacks
64 which grow downwards). */
67 pushl %edx /* Push address of the shared library
68 termination function. */
71 /* Load PIC register. */
73 addl $_GLOBAL_OFFSET_TABLE_, %ebx
75 /* Push address of our own entry points to .fini and .init. */
76 leal __libc_csu_fini@GOTOFF(%ebx), %eax
78 leal __libc_csu_init@GOTOFF(%ebx), %eax
81 pushl %ecx /* Push second argument: argv. */
82 pushl %esi /* Push first argument: argc. */
84 leal BP_SYM (main)@GOTOFF(%ebx), %eax
87 /* Call the user's main function, and exit with its value.
88 But let the libc call main. */
89 call BP_SYM (__libc_start_main)@PLT
91 /* Push address of our own entry points to .fini and .init. */
92 pushl $__libc_csu_fini
93 pushl $__libc_csu_init
95 pushl %ecx /* Push second argument: argv. */
96 pushl %esi /* Push first argument: argc. */
100 /* Call the user's main function, and exit with its value.
101 But let the libc call main. */
102 call BP_SYM (__libc_start_main)
105 hlt /* Crash if somehow `exit' does return. */
112 /* To fulfill the System V/i386 ABI we need this symbol. Yuck, it's so
113 meaningless since we don't support machines < 80386. */
120 /* Define a symbol for the first piece of initialized data. */
126 data_start = __data_start