Re: inline asm semantics: output constraint width smaller than input

From: H. Peter Anvin
Date: Fri Jan 23 2009 - 13:22:27 EST

Ingo Molnar wrote:


I am trying to build the kernel with LLVM 2.5 prerelease (using llvm-gcc-4.2 frontend), however I am running into some inline asm semantics issues, and after some discussion on LLVM bugzilla I would like to know if you would be accepting patches for this:

The problem is when "a" output constraint is used with a variable of smaller width than the "0" input constraint.

IMO, that's an LLVM bug and should be fixed in LLVM while it is in prerelease. That particular constraint is a serious one, and will haunt us for many years if we allow ourselves to go down the path of having to fix that every time it crops up.

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