Re: [Xen-devel] [PATCH v3 5/5] x86: remove usage of .skip with non-absolute expressions

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Jan 29, 2018 at 12:43:10PM +0000, Wei Liu wrote:
> On Mon, Jan 29, 2018 at 12:26:43PM +0000, Roger Pau Monne wrote:
> > Clang assembler doesn't support using .skip with non-absolute
> > expressions:
> > 
> 
> But so is GNU as. From its manual for .skip:
> 
> "This directive emits size bytes, each of value fill. Both size and fill
> are absolute expressions."

I guess clang and as have different interpretations of what's an
absolute expression. Sadly I don't seem to be able to find neither
definitions.

I've already reported this to upstream clang long time ago, but
it doesn't seem to make any progress:

https://bugs.llvm.org/show_bug.cgi?id=27369

And I don't think I can hack this myself.

> > entry.S:109:15: error: expected absolute expression
> >         .skip .Lcr4_alt_end - .Lcr4_alt, 0x90
> >               ^
> > 
> 
> OOI what makes .Lcr4_alt_end - .Lcr4_alt non-absolute?

Clang doesn't consider symbols as absolute expressions, at least in the
context of .skip.

Thanks, Roger.

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