Decompile x86 code with segment registers

[don1001]

Hi,
I was decompiling x86 code and noticed segment registers are not handled correctly e.g.

Asm:

.text:08048907 0x08048907:
.text:08048907    push ebp
.text:08048908    mov ebp, esp
.text:0804890a    sub esp, 0x38
.text:0804890d    mov eax, [ebp+0x08]
.text:08048910    mov [ebp-0x1C], eax
.text:08048913    mov eax, [ebp+0x0C]
.text:08048916    mov [ebp-0x20], eax
.text:08048919    mov eax, gs:[0x00000014]
.text:0804891f    mov [ebp-0x0C], eax
.text:08048922    xor eax, eax
.text:08048924    mov edx, [ebp-0x20]
.text:08048927    mov eax, [0x0804B1B8]
.text:0804892c    mov dword ptr [esp+0x0C], 0x00
.text:08048934    mov [esp+0x08], edx
.text:08048938    mov edx, [ebp-0x1C]
.text:0804893b    mov [esp+0x04], edx
.text:0804893f    mov [esp], eax
.text:08048942    call _recv
.text:08048947    mov ecx, [ebp-0x0C]
.text:0804894a    xor ecx, gs:[0x00000014] ;using a canary value stored at GS+0x14
.text:08048951    jz 0x08048958
.text:08048953    call ___stack_chk_fail
.text:08048958
.text:08048958 0x08048958:
.text:08048958    leave
.text:08048959    ret

IDA:

ssize_t __cdecl sub_8048907(void *a1, size_t a2)
{
  int v2; // ST2C_4@1
  ssize_t result; // eax@1
  int v4; // ecx@1

  v2 = *MK_FP(__GS__, 20);
  result = recv(fd, a1, a2, 0);
  v4 = *MK_FP(__GS__, 20) ^ v2;
  return result;
}

RetDec

// Address range: 0x8048907 - 0x8048959
int32_t function_8048907(int32_t * buf, int32_t length) {
    int32_t v1 = recv((int32_t)g10, buf, length, 0); // 0x8048942
    int32_t result; // 0x8048959
    if (*(int32_t *)20 != *(int32_t *)20) { //decompiled incorrectly
        // 0x8048953
        __stack_chk_fail();
        int32_t * v2;
        result = (int32_t)&v2;
        // branch -> 0x8048958
    } else {
        result = v1;
    }
    // 0x8048958
    return result;
}

Could you implement something like IDA does ? MK_FP make far pointer to handle gs, fs registers.

[PeterMatula]

Yeah, segments registers are kinda ignored right now, I will have to look into it - how to properly handle and represent this.

[PeterMatula]

This should be fixed by #391. I was adding some test for it, but since there is no sample here, I cannot add it. Try it yourself and re-open/report an issue if it does not work, or send me a sample to test.