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/* Startup code for FreeBSD/amd64 ABI.
Copyright (C) 2001, 2002, 2003 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Andreas Jaeger <aj@suse.de>, 2001.
FreeBSD modification by Petr Salinger, 2006.
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, 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 a few.
Blindly applied on amd64:
%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
But on amd64 %rsp also have to be 16-byte aligned,
standard C calling convention already passes arguments in registers.
FreeBSD uses %edi as pointer to arguments and environment, %rsp is passed aligned.
On entry from kernel, %rsp=%rdi or %rsp=%rdi-8,
on entry from ld.so, glibc might set up it slightly differently.
On FreeBSD, we use %rsi for passing function pointer to rtld_fini().
On entry from FreeBSD kernel, %rsi is cleared, %rdx is not cleared,
on entry from ld.so, glibc sets both %rsi and %rdx to point to rtld_fini().
Used interface (via %rdi, %rsi) is equal to standard C calling interface for
void _start(void *arg, void *rtld_fini());
*/
#include <sysdep.h>
#include <libc-symbols.h>
weak_extern (_end)
.text
.globl _start
.type _start,@function
_start:
cfi_startproc
cfi_undefined (rip)
/* Clear the frame pointer. The ABI suggests this be done, to mark
the outermost frame obviously. */
xorl %ebp, %ebp /* zero extending clears whole 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 %rsi, %r9 /* Address of the shared library termination
function. */
movq 0(%rdi), %rsi /* argument count. */
leaq 8(%rdi), %rdx /* argv starts just at above argc. */
/* 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
#ifdef SHARED
/* Pass address of our own entry points to .fini and .init. */
movq __libc_csu_fini@GOTPCREL(%rip), %r8
movq __libc_csu_init@GOTPCREL(%rip), %rcx
movq main@GOTPCREL(%rip), %rdi
/* Call the user's main function, and exit with its value.
But let the libc call main. */
call __libc_start_main@PLT
#else
/* Pass address of our own entry points to .fini and .init. */
movq $__libc_csu_fini, %r8
movq $__libc_csu_init, %rcx
movq $main, %rdi
/* Call the user's main function, and exit with its value.
But let the libc call main. */
call __libc_start_main
#endif
hlt /* Crash if somehow `exit' does return. */
/* just reference _end,
it is needed as global symbol for brk() usage,
it is a dead code on purpose. */
#ifdef SHARED
movq _end@GOTPCREL(%rip), %rax
#else
movq $_end, %rax
#endif
cfi_endproc
/* 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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