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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 <features.h>

.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