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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 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
- .global _start
- .global __uClibc_main
- .type _start,%function
- .type __uClibc_main,%function
- .text
- _start:
- /* clear the frame pointer */
- mov fp, #0
- /* 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 a3 */
- add r2, r1, r0, lsl #2
- add r2, r2, #4
- /* Ok, now run uClibc's main() -- shouldn't return */
- bl __uClibc_main
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