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/* When we enter this piece of code, the program stack looks like this:
argc argument counter (integer)
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
When we are done here, we want
a1=argc
a2=argv[0]
a3=argv[argc+1]
This file now uses the register naming from the ARM Procedure Calling Standard
Name Number APCS Role
a1 0 argument 1 / integer result / scratch register / argc
a2 1 argument 2 / scratch register / argv
a3 2 argument 3 / scratch register / envp
a4 3 argument 4 / scratch register
v1 4 register variable
v2 5 register variable
v3 6 register variable
v4 7 register variable
v5 8 register variable
sb/v6 9 static base / register variable
sl/v7 10 stack limit / stack chunk handle / reg. variable
fp 11 frame pointer
ip 12 scratch register / new-sb in inter-link-unit calls
sp 13 lower end of current stack frame
lr 14 link address / scratch register
pc 15 program counter
*/
.text
.align 2
.global __environ
.global _start
.global exit
.global main
.type _start,%function
.type exit,%function
.type main,%function
.text
_start:
/* clear the frame pointer */
mov fp, #0
/* Load register a1 (argc) from the stack to its final resting place */
ldr a1, [sp], #4
/* Copy argv pointer into a2 -- which its final resting place */
mov a2, sp
/* Set up environ, skip to the end of argv, and put
* a pointer to whatever we find there (hopefully the
environment) in a3 */
ldr a4, .L3
add a3, a2, a1, lsl #2
add a3, a3, #4
str a3, [a4, #0]
bl main
bl exit
.align 2
.L3:
.word __environ
.data
.align 2
.global __environ
__environ:
.long 0
.weak environ
environ = __environ
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