Currently having trouble (assembly and c)

[ChickenChowMinh]

I have this assembly code that I'm trying to convert to C. I'm currently having trouble understanding it though. I've tried to compile it with Nasm, but I get numerous amounts of error. It could be the way I'm compiling it though..because this code is supposed to work. Could anyone help me out understand what this means?

    .file    "mystery.c"
    .text
.globl add
    .type    add, @function
add:
    pushl    %ebp
    movl    %esp, %ebp
    movl    12(%ebp), %eax
    addl    8(%ebp), %eax
    popl    %ebp
    ret
    .size    add, .-add
.globl compute_fib
    .type    compute_fib, @function
compute_fib:
    pushl    %ebp
    movl    %esp, %ebp
    pushl    %ebx
    subl    $28, %esp
    movl    8(%ebp), %eax
    movl    num(,%eax,4), %eax
    cmpl    $-1, %eax
    je    .L4
    movl    8(%ebp), %eax
    movl    num(,%eax,4), %eax
    movl    %eax, -24(%ebp)
    jmp    .L6
.L4:
    movl    $-1, -8(%ebp)
    cmpl    $0, 8(%ebp)
    jne    .L7
    movl    $0, -8(%ebp)
    jmp    .L9
.L7:
    cmpl    $1, 8(%ebp)
    jne    .L10
    movl    $1, -8(%ebp)
    jmp    .L9
.L10:
    movl    8(%ebp), %eax
    subl    $2, %eax
    movl    %eax, (%esp)
    call    compute_fib
    movl    %eax, %ebx
    movl    8(%ebp), %eax
    subl    $1, %eax
    movl    %eax, (%esp)
    call    compute_fib
    movl    %ebx, 4(%esp)
    movl    %eax, (%esp)
    call    add
    movl    %eax, -8(%ebp)
.L9:
    movl    8(%ebp), %eax
    movl    num(,%eax,4), %eax
    cmpl    $-1, %eax
    jne    .L12
    movl    8(%ebp), %edx
    movl    -8(%ebp), %eax
    movl    %eax, num(,%edx,4)
.L12:
    movl    8(%ebp), %eax
    movl    num(,%eax,4), %eax
    movl    %eax, -24(%ebp)
.L6:
    movl    -24(%ebp), %eax
    addl    $28, %esp
    popl    %ebx
    popl    %ebp
    ret
    .size    compute_fib, .-compute_fib
    .section    .rodata
.LC0:
    .string    "Value:   %d\n"
    .text
.globl main
    .type    main, @function
main:
    leal    4(%esp), %ecx
    andl    $-16, %esp
    pushl    -4(%ecx)
    pushl    %ebp
    movl    %esp, %ebp
    pushl    %ecx
    subl    $36, %esp
    movl    4(%ecx), %eax
    addl    $4, %eax
    movl    (%eax), %eax
    movl    %eax, (%esp)
    call    atoi
    movl    %eax, -12(%ebp)
    movl    $0, -8(%ebp)
    jmp    .L16
.L17:
    movl    -8(%ebp), %eax
    movl    $-1, num(,%eax,4)
    addl    $1, -8(%ebp)
.L16:
    cmpl    $199, -8(%ebp)
    jle    .L17
    movl    -12(%ebp), %eax
    movl    %eax, (%esp)
    call    compute_fib
    movl    %eax, 4(%esp)
    movl    $.LC0, (%esp)
    call    printf
    movl    $0, %eax
    addl    $36, %esp
    popl    %ecx
    popl    %ebp
    leal    -4(%ecx), %esp
    ret
    .size    main, .-main
    .comm    num,800,32
    .ident    "GCC: (GNU) 4.1.2 20080704 (Red Hat 4.1.2-51)"
    .section    .note.GNU-stack,"",@progbits

[GReaper]

No wonder why you can't understand it and it's giving you errors. This assembly is the output of GCC, which is then fed into GASM to assemble. It's not meant for NASM.

EDIT: Pass this assembly to GCC as *.s in order to assemble and link it.

[ChickenChowMinh]

Okay, so I trying to do this, but the command I'm putting in may be wrong.

command: "gcc -c mystery.s"

I keep getting these errors..
error: suffix or operands invalid for 'push'
error: suffix or operands invalid for 'pop'

[Salem]

But are you trying to compile this 32-bit code on a 64 bit machine?

I get the same errors when compiling in 64-bit mode.

However,

$ gcc -Wa,--32  bar.s
/usr/bin/ld: i386 architecture of input file `/tmp/ccyHtwVV.o' is incompatible with i386:x86-64 output
collect2: ld returned 1 exit status

shows it will compile OK as 32-bit code, but without the necessary libraries, it still won't create an executable file.

Besides, how much "mystery" can there be in a file containing a function called compute_fib which calls itself recursively.

[ChickenChowMinh]

haha you're right. I was too busy looking at the first few lines of main that I didn't realize that this program actually computes fibonacci values. Thanks so much.