uclibc-ng/libc/sysdeps/linux/arm/crt0pic.S

/* 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


@ 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

	/* pull argc, argv and envp off the stack */
	ldr r0,[sp, #0]
	ldr r1,[sp, #4]
	ldr r2,[sp, #8]

	/* Ok, now run uClibc's main() -- shouldn't return */
	bl	__uClibc_main