Bug 30418 - use of labels that happen to match register names or keywords
Summary: use of labels that happen to match register names or keywords
Status: UNCONFIRMED
Alias: None
Product: binutils
Classification: Unclassified
Component: gas (show other bugs)
Version: unspecified
: P2 normal
Target Milestone: ---
Assignee: Not yet assigned to anyone
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2023-05-04 04:04 UTC by LIU Hao
Modified: 2024-01-26 19:05 UTC (History)
3 users (show)

See Also:
Host:
Target: x86_64-*-*
Build:
Last reconfirmed:


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Description LIU Hao 2023-05-04 04:04:36 UTC
Possible dup of https://sourceware.org/bugzilla/show_bug.cgi?id=12240

This is how MSVC handles such names:
(https://gcc.godbolt.org/z/TonjYaxqj)

```
static int* volatile rip;
static unsigned int volatile eax;

int
get_value(void)
  {
    return rip[eax];
  }
```

MSVC outputs:
```
get_value PROC                                      ; COMDAT
        mov     ecx, DWORD PTR eax
        mov     rax, QWORD PTR rip
        mov     eax, DWORD PTR [rax+rcx*4]
        ret     0
get_value ENDP
```

GCC outputs:
```
get_value:
        mov     rdx, QWORD PTR rip[rip]
        mov     eax, DWORD PTR eax[rip]
        mov     eax, DWORD PTR [rdx+rax*4]
        ret
```

In the case of MSVC, `DWORD PTR eax` is unambiguously parsed as the label `eax` and `DWORD PTR [eax]` is unambiguously parsed as the register `eax`. The address of all labels are always relative to RIP, but it is implied, and brackets are not written explicitly.
Comment 1 LIU Hao 2023-05-04 04:06:57 UTC
I'm gonna file another report to GCC for removal of the explicit RIP and bracket.