Messages in this thread | | | Date | Fri, 23 Jan 2009 22:42:47 +0200 | From | Török Edwin <> | Subject | Re: inline asm semantics: output constraint width smaller than input |
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On 2009-01-23 20:52, Török Edwin wrote: > On 2009-01-23 20:30, Ingo Molnar wrote: > >> * Török Edwin <edwintorok@gmail.com> wrote: >> >> >> >>> Having said that, llvm-gcc is not yet able to compile the full Linux >>> kernel on its own [for example the boot code, due to asm(".code16gcc")], >>> but with LLVM 2.4 it was possible to build "arch=UM", and "arch=X86" (by >>> using gcc to build the bootcode). I'd like LLVM 2.5 to be able to build >>> the kernel, so I'll file bugs for llvm/kernel depending on where the >>> problem is. >>> >>> >> Could we get LLVM folks on the Cc: and see how difficult it would be to >> fix this on the LLVM side? Asm constraints are used all around the place >> and different input/output types are very common. >> > >
Hi Ingo,
Could you describe what are the semantics you need for inline asm constraints in the kernel? GCC doesn't document all the corner cases, and defining inline asm = "whatever gcc accepts" is not very useful for LLVM.
So far we've encountered the problem with input/output operand tied to same register, but having different widths: - output wider than input, both integers: do you need this case? - output narrower than input, both integers: this is the common case, right? - can it also happen that input is pointer, output is integer of different width? - .. any other mismatches?
Could you also describe why put_user/the example from pcbios needs the different widths?
Best regards, --Edwin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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