1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
|
/* 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
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
When we are done here, we want
a1=argc
a2=argv[0]
a3=argv[argc+1]
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
*/
#include <features.h>
.text
.global _start
.global __uClibc_main
.type _start,%function
.type __uClibc_main,%function
.text
_start:
#if 0 /* some old code the I feel should not be here - davidm */
@ adjust the data segment base pointer
ldr r3,=__data_start
sub sl,sl,r3
mov BASEREG,sl
#endif
/* clear the frame pointer */
mov fp, #0
#ifdef __UCLIBC_HAS_MMU__
/* Load register r0 (argc) from the stack to its final resting place */
ldr r0, [sp], #4
/* Copy argv pointer into r1 -- which its final resting place */
mov r1, sp
/* Skip to the end of argv and put a pointer to whatever
we find there (hopefully the environment) in r2 */
add r2, r1, r0, lsl #2
add r2, r2, #4
#else
/*
* uClinux stacks look a little different to MMU stacks
* for no good reason
*/
/* pull argc, argv and envp off the stack */
ldr r0,[sp, #0]
ldr r1,[sp, #4]
ldr r2,[sp, #8]
#endif
/* Ok, now run uClibc's main() -- shouldn't return */
bl __uClibc_main
/* Stick in a dummy reference to main(), so that if an application
* is linking when the main() function is in a static library (.a)
* we can be sure that main() actually gets linked in */
L_dummy_main_reference:
.long main
|
