1 /* Startup code compliant to the ELF i386 ABI.
2 Copyright (C) 1995, 1996, 1997, 1998, 2000, 2001, 2002, 2003, 2004
3 Free Software Foundation, Inc.
4 This file is part of the GNU C Library.
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
11 In addition to the permissions in the GNU Lesser General Public
12 License, the Free Software Foundation gives you unlimited
13 permission to link the compiled version of this file with other
14 programs, and to distribute those programs without any restriction
15 coming from the use of this file. (The GNU Lesser General Public
16 License restrictions do apply in other respects; for example, they
17 cover modification of the file, and distribution when not linked
18 into another program.)
20 Note that people who make modified versions of this file are not
21 obligated to grant this special exception for their modified
22 versions; it is their choice whether to do so. The GNU Lesser
23 General Public License gives permission to release a modified
24 version without this exception; this exception also makes it
25 possible to release a modified version which carries forward this
28 The GNU C Library is distributed in the hope that it will be useful,
29 but WITHOUT ANY WARRANTY; without even the implied warranty of
30 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
31 Lesser General Public License for more details.
33 You should have received a copy of the GNU Lesser General Public
34 License along with the GNU C Library; if not, write to the Free
35 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
38 /* This is the canonical entry point, usually the first thing in the text
39 segment. The SVR4/i386 ABI (pages 3-31, 3-32) says that when the entry
40 point runs, most registers' values are unspecified, except for:
42 %edx Contains a function pointer to be registered with `atexit'.
43 This is how the dynamic linker arranges to have DT_FINI
44 functions called for shared libraries that have been loaded
45 before this code runs.
47 %esp The stack contains the arguments and environment:
52 (4*(argc+1))(%esp) envp[0]
61 .type _start,%function
62 #if defined(__UCLIBC_CTOR_DTOR__)
70 .type __uClibc_main,%function
72 /* Clear the frame pointer. The ABI suggests this be done, to mark
73 the outermost frame obviously. */
76 /* Extract the arguments as encoded on the stack and set up
77 the arguments for `main': argc, argv. envp will be determined
78 later in __libc_start_main. */
79 popl %esi /* Pop the argument count. */
80 movl %esp, %ecx /* argv starts just at the current stack top.*/
82 /* Before pushing the arguments align the stack to a 16-byte
83 (SSE needs 16-byte alignment) boundary to avoid penalties from
84 misaligned accesses. Thanks to Edward Seidl <seidl@janed.com>
85 for pointing this out. */
86 andl $0xfffffff0, %esp
87 pushl %eax /* Push garbage because we allocate
90 /* Provide the highest stack address to the user code (for stacks
91 which grow downwards). */
94 pushl %edx /* Push address of the shared library
95 termination function. */
98 /* Load PIC register. */
102 addl $_GLOBAL_OFFSET_TABLE_+[.-.L0],%ebx
104 /* Push address of our own entry points to .fini and .init. */
105 pushl _fini@GOT(%ebx)
106 pushl _init@GOT(%ebx)
108 pushl %ecx /* Push second argument: argv. */
109 pushl %esi /* Push first argument: argc. */
113 /* Call the user's main function, and exit with its value.
114 But let the libc call main. */
115 call __uClibc_main@PLT
117 /* Push address of our own entry points to .fini and .init. */
121 pushl %ecx /* Push second argument: argv. */
122 pushl %esi /* Push first argument: argc. */
126 /* Call the user's main function, and exit with its value.
127 But let the libc call main. */
131 hlt /* Crash if somehow `exit' does return. */
132 .size _start,.-_start
134 /* Define a symbol for the first piece of initialized data. */
140 data_start = __data_start