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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

   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 

.text

        .global _start

        .type   _start,%function

#if defined L_crt0 || ! defined __UCLIBC_CTOR_DTOR__

        .type   __uClibc_main,%function

#else

        .weak   _init

        .weak   _fini

        .type   __uClibc_start_main,%function

#endif

/* 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 */

        .type   main,%function

.text

_start:

        /* 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 from normal

         * MMU-full Linux 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

#if (defined L_crt1 || defined L_gcrt1 ) && defined __UCLIBC_CTOR_DTOR__

        /* Store the address of _init in r3 as an argument to main() */

        ldr r3, =_init

        /* Push _fini onto the stack as the final argument to main() */

        ldr r4, =_fini

        stmfd sp!, {r4}

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

        bl      __uClibc_start_main

#else

        bl      __uClibc_main

#endif

        /* Crash if somehow `exit' returns anyways.  */

        bl abort

/* We need this stuff to make gdb behave itself, otherwise

   gdb will chokes with SIGILL when trying to debug apps.

*/

        .section ".note.ABI-tag", "a"

        .align 4

        .long 1f - 0f

        .long 3f - 2f

        .long  1

0:      .asciz "GNU"

1:      .align 4

2:      .long 0

        .long 2,0,0

3:      .align 4

#if defined L_gcrt1 && defined __UCLIBC_PROFILING__

# include "./gmon-start.S"

#endif