CODEWITHSUNDEEP
macosassemblyx86-64intel-syntax
Miguel Guerra
Miguel Guerra

Reputation: 165

error in backend: 32-bit absolute addressing is not supported in 64-bit mode

I'm working on ASM intel_syntax noprefix on a mac using gcc, and for some reason I keep getting this error in backend: 32-bit absolute addressing is not supported in 64-bit mode

Does this have something to do with the variables, since, at the moment, I've been using the ASM inline?

Here's my code:

#include <stdio.h>

char c, b;

int main() {

    printf("Give me letter: ");
    scanf(" %c", &c);
    
_

    _asm(   ".intel_syntax noprefix;"
        "xor eax, eax;"     // clear eax
        "mov al, byte ptr [c];" // save c in eax
        "cmp eax, 65;"      // eax ? "A"
        "jl Fin;"       // eax < "A" -> Fin
        "cmp eax, 90;"      // eax ? "Z"
        "jg UpC;"       // eax >= Z -> Up Case
        "add eax, 32;"      // make low case
        "jmp Fin;"      // -> Fin   
    "UpC:   cmp eax, 97;"       // eax ? "a"
        "jl Fin;"       // eax < "a" -> Fin
        "cmp eax, 122;"     // eax ? "z"
        "jg Fin;"       // eax > "z" -> Fin
        "sub eax, 32;"      // make Up Case
    "Fin:   mov byte ptr [b], al;"  // save res in b
        ".att_syntax");
    
    printf("Case changed : %c\n", b);
}

Upvotes: 8

Views: 8159

Answers (1)

Jester
Jester

Reputation: 58762

Yes, as the error says, on osx you are not allowed to use absolute references which byte ptr [c] assembles to. As a workaround you could try byte ptr c[rip].

Note that it is very bad practice to switch syntax in inline assembly block, you should use -masm=intel compiler switch. Also, gcc inline asm is not supposed to be used like that, normally you use the constraint mechanism to reference arguments.

Upvotes: 6

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