Geek Answers Handbook

Download ELF on MIPS, malloc issue

I am uploading a simple statically linked ELF binary to MIPS (32-bit). After matching loadable segments, this is how I set up the stack before moving on to my ELF CRT target function _start:

__asm__("                                                             \
      addi       $2,         %[envN],      0                         ;\
    .env_loop:                                                        \
      addi       $2,         $2,          -4                         ;\
      lw         $3,         0($2)                                   ;\
      addi       $sp,        $sp,         -4                         ;\
      sw         $3,         0($sp)                                  ;\
      bne        $2,         %[env0],      .env_loop                 ;\
      addi       $2,         %[argN],      0                         ;\
    .arg_loop:                                                        \
      addi       $2,         $2,          -4                         ;\
      lw         $3,         0($2)                                   ;\
      addi       $sp,        $sp,         -4                         ;\
      sw         $3,         0($sp)                                  ;\
      bne        $2,         %[arg0],      .arg_loop                 ;\
      addi       $2,         %[argc],      0                         ;\
      addi       $sp,        $sp,         -4                         ;\
      sw         $2,         0($sp)                                  ;\
      addi       $2,         %[func],      0                         ;\
      jr         $2                                                  ;"
    :
    : [envN] "r" (envp + envc + 1),
      [env0] "r" (envp),
      [argN] "r" (argv + argc + 1),
      [arg0] "r" (argv),
      [argc] "r" ((int32_t)argc),
      [func] "r" (entry_point)
    : "$2", "$3", "cc", "memory"
);

So I push the environment variables, command line arguments, argcon the stack, and finally jump to the target ELF entry point. This works correctly, and I end up inside my loaded main program function with the correct command line arguments and all but one: it mallocdoes not work! Any call returns null to it and sets errno to ENOMEM.

MIPS, (qemu-system-mips), , , , . , ; x86, x86_64 arm, , - malloc MIPS .

-, ? -, , MIPS, , ? , , - , , .

Linux musl libc. , musl expand_heap, , , (musl malloc , ).

( libc; ), (printf, fopen ..) , -, malloc (, , realloc/calloc, , ). .

+4
2

, MIPS, , aux :

// main() pseudo arguments.
#define AT_PAGESZ 6
argv:
        .word   name
        .word   0                       // End of argv.
        .word   0                       // End of envp.
        // Auxv
        .word   AT_PAGESZ
        .word   4096                    // Page size.
        .word   0

, auxv MIPS musl.

+3

MIPS, , " ", 3-30 MIPS ABI, : http://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf - ?

+1

More articles:


All Articles