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Diffstat (limited to 'sysdeps/i386/start.S')
| -rw-r--r-- | sysdeps/i386/start.S | 141 |
1 files changed, 141 insertions, 0 deletions
diff --git a/sysdeps/i386/start.S b/sysdeps/i386/start.S new file mode 100644 index 0000000000..990f3715d5 --- /dev/null +++ b/sysdeps/i386/start.S @@ -0,0 +1,141 @@ +/* Startup code compliant to the ELF i386 ABI. + Copyright (C) 1995-2012 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 "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 <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 SHARED + /* Load PIC register. */ + call 1f + addl $_GLOBAL_OFFSET_TABLE_, %ebx + + /* Push address of our own entry points to .fini and .init. */ + leal __libc_csu_fini@GOTOFF(%ebx), %eax + pushl %eax + leal __libc_csu_init@GOTOFF(%ebx), %eax + pushl %eax + + pushl %ecx /* Push second argument: argv. */ + pushl %esi /* Push first argument: argc. */ + + pushl BP_SYM (main)@GOT(%ebx) + + /* Call the user's main function, and exit with its value. + But let the libc call main. */ + call BP_SYM (__libc_start_main)@PLT +#else + /* 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) +#endif + + hlt /* Crash if somehow `exit' does return. */ + +#ifdef SHARED +1: movl (%esp), %ebx + ret +#endif + +/* 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 |