[llvm-dev] Automake Assembler Assumptions with LLVM-MC

Daniel Sanders via llvm-dev llvm-dev at lists.llvm.org
Wed May 18 06:10:50 PDT 2016


It's my understanding that llvm-mc is intended to be a testing tool for LLVM developers rather than an assembler for end users. Users should be assembling with clang.

> -----Original Message-----
> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of John
> Leidel (jleidel) via llvm-dev
> Sent: 18 May 2016 13:35
> To: llvm-dev at lists.llvm.org
> Subject: [llvm-dev] Automake Assembler Assumptions with LLVM-MC
> All, we recently had a user report an issue associated with utilizing LLVM-MC
> as the desired assembler in place of GNU’s GAS.  They are utilizing a tangled
> mess of automake scripts to build this respective software package and have
> decided to manually override the “CCAS” macro to point directly to LLVM-MC
> (rather than using Clang).  Apparently, automake assumes that whatever
> “compiler” (as it is referenced in the automake documentation) is used for
> assembling files must accept the “-c” and “-o” options.  LLVM-MC correctly
> yells at the user given that “-c” is not a valid option (as it should).  However,
> GAS does not.  It happily accepts “-c” as a valid option.  We peered into the
> Bintutils 2.24 source and there is no explicit “-c” option support.  This appears
> to be an option parsing bug in Binutils that either 1) collides with a known
> long option or 2) somehow wanders into the “-ac” parsing logic.  Either way,
> its not a valid option that does anything.
> Given that LLVM-MC has basic support for handling GNU GAS options, what’s
> the policy on being “bug for bug” compatible with GAS?  My personal opinion
> is the user should fall back to using the compiler frontend to build their
> assembly options, but this is a valid question nonetheless.  Thoughts?
> Automake documentation on this topic is here:
> https://www.gnu.org/software/automake/manual/html_node/Assembly-
> Support.html
> - John D. Leidel
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