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/* Startup code for ARM & ELF
Copyright (C) 1995, 1996, 1997, 1998, 2001, 2002 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.
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.
Note that the code in the .init section has already been run.
This includes _init and _libc_init
At this entry point, most registers' values are unspecified, except:
a1 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.
sp The stack contains the arguments and environment:
0(sp) argc
4(sp) argv[0]
...
(4*argc)(sp) NULL
(4*(argc+1))(sp) envp[0]
...
NULL
*/
/*
For uClinux it looks like this:
argc argument counter (integer)
argv char *argv[]
envp char *envp[]
argv[0] program name (pointer)
argv[1...N] program args (pointers)
argv[argc-1] end of args (integer)
NULL
env[0...N] environment variables (pointers)
NULL
ARM register quick reference:
Name Number ARM Procedure Calling Standard Role
a1 r0 argument 1 / integer result / scratch register / argc
a2 r1 argument 2 / scratch register / argv
a3 r2 argument 3 / scratch register / envp
a4 r3 argument 4 / scratch register
v1 r4 register variable
v2 r5 register variable
v3 r6 register variable
v4 r7 register variable
v5 r8 register variable
sb/v6 r9 static base / register variable
sl/v7 r10 stack limit / stack chunk handle / reg. variable
fp r11 frame pointer
ip r12 scratch register / new-sb in inter-link-unit calls
sp r13 lower end of current stack frame
lr r14 link address / scratch register
pc r15 program counter
*/
.text
.globl _start
.type _start,#function
_start:
/* Clear the frame pointer and link register since this is the outermost frame. */
mov fp, #0
mov lr, #0
/* Pop argc off the stack and save a pointer to argv */
ldr a2, [sp], #4
mov a3, sp
/* Push stack limit */
str a3, [sp, #-4]!
/* Push rtld_fini */
str a1, [sp, #-4]!
#ifdef __PIC__
ldr sl, .L_GOT
.L_GOT_OFF:
add sl, pc, sl
ldr ip, .L_GOT+4 /* _fini */
ldr a1, [sl, ip]
str a1, [sp, #-4]! /* Push _fini */
ldr ip, .L_GOT+8 /* _init */
ldr a4, [sl, ip]
ldr ip, .L_GOT+12 /* main */
ldr a1, [sl, ip]
/* __uClibc_main (main, argc, argv, init, fini, rtld_fini, stack_end) */
/* Let the libc call main and exit with its return code. */
b __uClibc_main(PLT)
#else
/* Fetch address of fini */
ldr ip, =_fini
/* Push fini */
str ip, [sp, #-4]!
/* Set up the other arguments in registers */
ldr a1, =main
ldr a4, =_init
/* __uClibc_main (main, argc, argv, init, fini, rtld_fini, stack_end) */
/* Let the libc call main and exit with its return code. */
b __uClibc_main
#endif
#ifdef __PIC__
.L_GOT:
.word _GLOBAL_OFFSET_TABLE_-(.L_GOT_OFF+8)
.word _fini(GOT)
.word _init(GOT)
.word main(GOT)
#endif
/* 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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