Re: Feature Request: Add Intel/NASM Syntax Option for Inline Assembly

LIU Hao via Gcc-help <[email protected]> Tue, 16 Dec 2025 10:10:10 +0800

Newsgroups	gmane.comp.gcc.help
Message-ID	<[email protected]>

在 2025-12-16 06:42, Tadeo The rocket builder via Gcc-help 写道:
> Would it be possible to add support for Intel syntax in inline assembly?
> For example:
> - Keep the existing __asm__ keyword with AT&T syntax for compatibility
> - Add a new keyword like __asm_intel__ or __asmnasm__ for Intel/NASM syntax
> - Or add a syntax flag/attribute to switch between syntaxes
> 
> This would greatly help OS developers who primarily use NASM for their .asm
> files and want consistent syntax when using inline assembly in C code.

NASM is essentially a new dialect. Given how assembly templates are hard-coded in GCC source, it would 
require adding a third dialect here and there.

Besides, GCC passes inline assembly to the assembler without parsing, so it doesn't do translation; in 
that case you need Clang, which does not support NASM syntax either.


> I'm currently developing CoolisOS (an x86-64 operating system) and this
> feature would make the codebase more maintainable.
> 
> Thank you for considering this request!

My best advice is to build everything with `-masm=intel` and stick to MASM syntax; it's supported by all 
compilers and provides best compatibility.

There's a pitfall, however:

    MASM:  vaddps ymm0, ymm1, DWORD BCST [rax]
    LLVM:  vaddps ymm0, ymm1, DWORD PTR [rax]{1to8}
    NASM:  vaddps ymm0, ymm1, DWORD [rax]{1to8}

GAS accepts both MASM and LLVM syntax, but all the other assemblers choke on each other's syntax. It's 
quite tricky.



-- 
Best regards,
LIU Hao

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