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As this question shows, with g++, I can do g++ -S -masm=intel test.cpp. Also, with clang, I can do clang++ -S test.cpp, but -masm=intel is not supported by clang (warning argument unused during compilation: -masm=intel). How do I get intel syntax with clang?

Community
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Jesse Good
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3 Answers3

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As noted below by @thakis, newer versions of Clang (3.5+) accept the -masm=intel argument.

For older versions, this should get clang to emit assembly code with Intel syntax:

clang++ -S -mllvm --x86-asm-syntax=intel test.cpp

You can use -mllvm <arg> to pass in llvm options from the clang command line. Sadly this option doesn't appear to be well documented, and thus I only found it by browsing through the llvm mailing lists.

Brennan Vincent
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dcoles
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    http://llvm.org/bugs/show_bug.cgi?id=17465 requests support for -masm=intel and beyond. – Trass3r Oct 22 '13 at 15:30
  • @dcoles Not working for clang 3.7. I executed `$clang -S -mllvm --x86-asm-syntax=intel file.c`. Am I doint something wrong here? It's not giving any error and silently exiting. – Saumya Suhagiya Aug 06 '15 at 16:28
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    @saumya-suhagiya I've just confirmed that this still works with clang 3.8.0-svn244195-1~exp1. The command shown above will generate a file called `test.s`. You change this output location to a custom location using the `-o ` option. – dcoles Aug 06 '15 at 16:58
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    @dcoles Hi, perhaps a not so smart question. Is it possible to compile and link the assembly code with `nasm`? – Alexander Cska Jan 29 '16 at 21:55
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    @AlexanderCska I'm not sure this is possible without some manual fixup. While the syntax for NASM is similar to Intel's, there is some incompatibilities between them. – dcoles Feb 02 '16 at 23:20
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As of clang r208683 (clang 3.5+), it understands -masm=intel. So if your clang is new enough, you can just use that.

thakis
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  • It seems to me that the code generated by `-masm=intel` cannot be compiled by `clang` again? I am running clang 3.8. – Yai0Phah Jun 12 '19 at 11:56
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Presuming you can have Clang emit normal LLVM byte codes, you can then use llc to compile to assembly language, and use its --x86-asm-syntax=intel option to get the result in Intel syntax.

Kerrek SB
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Jerry Coffin
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  • Thanks again. I also found out `llc` by default turns optimizations on (-02) while gcc and clang use no optimizations (-O0) by default (it took me forever to figure out why the assembly output was different). – Jesse Good Jun 12 '12 at 04:18