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/* Startup code compliant to the ELF x86-64 ABI.
Copyright (C) 2001 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Andreas Jaeger <aj@suse.de>, 2001.
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.
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, 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:
%rdx 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.
%rsp The stack contains the arguments and environment:
0(%rsp) argc
8(%rsp) argv[0]
...
(8*argc)(%rsp) NULL
(8*(argc+1))(%rsp) 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. */
xorq %rbp, %rbp
/* Extract the arguments as encoded on the stack and set up
the arguments for __libc_start_main (int (*main) (int, char **, char **),
int argc, char *argv,
void (*init) (void), void (*fini) (void),
void (*rtld_fini) (void), void *stack_end).
The arguments are passed via registers and on the stack:
main: %rdi
argc: %rsi
argv: %rdx
init: %rcx
fini: %r8
rtld_fini: %r9
stack_end: stack. */
movq %rdx, %r9 /* Address of the shared library termination
function. */
popq %rsi /* Pop the argument count. */
movq %rsp, %rdx /* argv starts just at the current stack top. */
/* Align the stack to a 16 byte boundary to follow the ABI. */
andq $~15, %rsp
pushq %rax /* Push garbage because we push 8 more bytes. */
/* Provide the highest stack address to the user code (for stacks
which grow downwards). */
pushq %rsp
/* Pass address of our own entry points to .fini and .init. */
movq $_fini, %r8
movq $_init, %rcx
movq $BP_SYM (main), %rdi
/* Call the user's main function, and exit with its value.
But let the libc call main. */
call BP_SYM (__libc_start_main)
hlt /* Crash if somehow `exit' does return. */
/* 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
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