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I am porting xv6 from GCC to Clang, and met the following error message:

clang -m32 -gdwarf-2 -Wa,-divide   -c -o swtch.o swtch.S
clang-3.8: error: unsupported argument '-divide' to option 'Wa,'

Note that -Wa is used to pass arguments to the assembler, and I couldn't figure out what is the -divide option.

As a fix, currently I switched off the integrated assembler by passing the no-integrated-as option to Clang. But I want to use Clang's integrated assember. Is it safe to ignore this option? Or is there an alternative way to give that option to Clang?

Jeehoon Kang
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1 Answers1

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The gas manual documentation for --divide says:

On SVR4-derived platforms, the character / is treated as a comment character, which means that it cannot be used in expressions. The --divide option turns / into a normal character. This does not disable / at the beginning of a line starting a comment, or affect using `#' for starting a comment.

On my Linux desktop, --divide does nothing: as assembles mov $(15/2), %eax just fine with or without --divide.

So you should be fine to take it out. If it's a problem and clang does treat / as a comment character on some platforms, it should usually result in build-time failure, not binaries with hidden bugs.

And yes, -divide apparently does the same thing as --divide. But you might want to try --divide in case clang's assembler only supports the more-standard double-- form.

Peter Cordes
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