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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]
ARM register quick reference:
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
@ r0 = argc
@ r1 = argv
@ r2 = envp
@ sl = data segment
#define BASEREG r9
.text
_start:
@ adjust the data segment base pointer
ldr r3,=__data_start
sub sl,sl,r3
mov BASEREG,sl
ldr r3, .L3
str r2,[BASEREG,r3]
/* pull argc, argv and envp off the stack */
ldr r0,[sp, #0]
ldr r1,[sp, #4]
ldr r2,[sp, #8]
bl main
/* ldr r0,=0 */
bl exit
.align 2
.L3:
.word __environ
.data
.align 2
.global __environ
__environ:
.long 0
.weak environ
environ = __environ
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