Re: [PATCH] build/xen: fix symbol generation with LLVM LD

["Roger Pau Monné" <roger.pau@citrix.com>]

On Fri, May 06, 2022 at 02:56:56PM +0200, Jan Beulich wrote:
> On 05.05.2022 16:21, Roger Pau Monne wrote:
> > --- a/xen/include/xen/compiler.h
> > +++ b/xen/include/xen/compiler.h
> > @@ -125,10 +125,11 @@
> >  #define __must_be_array(a) \
> >    BUILD_BUG_ON_ZERO(__builtin_types_compatible_p(typeof(a), typeof(&a[0])))
> >  
> > -#ifdef CONFIG_CC_HAS_VISIBILITY_ATTRIBUTE
> > -/* Results in more efficient PIC code (no indirections through GOT or PLT). */
> > -#pragma GCC visibility push(hidden)
> > -#endif
> > +/*
> > + * Results in more efficient PIC code (no indirections through GOT or PLT)
> > + * and is also required by some of the assembly constructs.
> > + */
> > +#pragma GCC visibility push(protected)
> >  
> >  /* Make the optimizer believe the variable can be manipulated arbitrarily. */
> >  #define OPTIMIZER_HIDE_VAR(var) __asm__ ( "" : "+g" (var) )
> 
> This has failed my pre-push build test, with massive amounts of errors
> about asm() constraints in the alternative call infrastructure. This
> was with gcc 11.3.0.

Hm, great. I guess I will have to use protected with clang and hidden
with gcc then, for lack of a better solution.

I'm slightly confused as to why my godbolt example:

https://godbolt.org/z/chTnMWxeP

Seems to work with gcc 11 then.  I will have to investigate a bit I
think.

Thanks, and sorry for the trouble.