/* Startup code compliant to the ELF i386 ABI. Copyright (C) 1995, 1996, 1997, 1998, 2000, 2001, 2002, 2003, 2004 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. In addition to the permissions in the GNU Lesser General Public License, the Free Software Foundation gives you unlimited permission to link the compiled version of this file with other programs, and to distribute those programs without any restriction coming from the use of this file. (The GNU Lesser General Public License restrictions do apply in other respects; for example, they cover modification of the file, and distribution when not linked into another program.) Note that people who make modified versions of this file are not obligated to grant this special exception for their modified versions; it is their choice whether to do so. The GNU Lesser General Public License gives permission to release a modified version without this exception; this exception also makes it possible to release a modified version which carries forward this exception. 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, see <http://www.gnu.org/licenses/>. */ /* 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 <features.h> .text .global _start .type _start,%function #if defined(__UCLIBC_CTOR_DTOR__) .type _init,%function .type _fini,%function #else .weak _init .weak _fini #endif .type main,%function .type __uClibc_main,%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 <seidl@janed.com> 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. */ #ifdef __PIC__ /* Load PIC register. */ call .L0 .L0: pop %ebx addl $_GLOBAL_OFFSET_TABLE_+[.-.L0],%ebx /* Push address of our own entry points to .fini and .init. */ pushl _fini@GOT(%ebx) pushl _init@GOT(%ebx) pushl %ecx /* Push second argument: argv. */ pushl %esi /* Push first argument: argc. */ pushl main@GOT(%ebx) /* Call the user's main function, and exit with its value. But let the libc call main. */ call __uClibc_main@PLT #else /* 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 __uClibc_main #endif hlt /* Crash if somehow `exit' does return. */ .size _start,.-_start /* Define a symbol for the first piece of initialized data. */ .data .global __data_start __data_start: .long 0 .weak data_start data_start = __data_start