Can I use Intel syntax of x86 assembly with GCC?

c gcc assembly x86 inline-assembly
Hlib picture Hlib · Feb 19, 2012 · Viewed 39.9k times · Source

I want to write a small low level program. For some parts of it I will need to use assembly language, but the rest of the code will be written on C/C++.

So, if I will use GCC to mix C/C++ with assembly code, do I need to use AT&T syntax or can I use Intel syntax? Or how do you mix C/C++ and asm (intel syntax) in some other way?

I realize that maybe I don't have a choice and must use AT&T syntax, but I want to be sure..

And if there turns out to be no choice, where I can find full/official documentation about the AT&T syntax?

Thanks!

Answer

ninjalj picture ninjalj · Feb 19, 2012

If you are using separate assembly files, gas has a directive to support Intel syntax:

.intel_syntax noprefix

which uses Intel syntax and doesn't need the % prefix before register names.

(You can also run as with -msyntax=intel -mnaked-reg to have that as the default instead of att, in case you don't want to put .intel_syntax noprefix at the top of your files.)

If you are using inline assembly, you can compile your C/C++ sources with gcc -masm=intel (See How to set gcc to use intel syntax permanently? for details.) This may not work with clang.

Using .intel_syntax noprefix at the start of inline asm, and switching back with .att_syntax can work, but will break if you use any m constraints. The memory reference will still be generated in AT&T syntax.

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