From: Kirill A. Korinsky <kirill@korins.ky>
Subject: Re: ld.so/sparc64: fix UA64 relocation mask selection and byte order
To: Mark Kettenis <mark.kettenis@xs4all.nl>
Cc: tech@openbsd.org
Date: Thu, 09 Jul 2026 17:24:32 +0200

On Thu, 09 Jul 2026 17:01:34 +0200,
Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> 
> > Date: Thu, 09 Jul 2026 15:30:52 +0200
> > From: Kirill A. Korinsky <kirill@korins.ky>
> > 
> > On Thu, 09 Jul 2026 14:55:45 +0200,
> > Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> > > 
> > > I think we do.  These "unaligned" relocations might not work in a
> > > multi-threaded context as threads may observed a partially updated
> > > state.
> > 
> > Make sense. This, actually, not that hard to change.
> > 
> > Something like that should do it.
> 
> And what about the UA32 and UA16 relocations?
>

As far as I see the code of lld it do not allow UA32 and UA16 for dynamic reallocations.

> 
> > I will include it into my large llvm-toolchain diff and into PR for llvm-upstream.
> > 
> > diff --git gnu/llvm/lld/ELF/SyntheticSections.cpp gnu/llvm/lld/ELF/SyntheticSections.cpp
> > index 57fcfc4cf3a..14ef5ed3c5b 100644
> > --- gnu/llvm/lld/ELF/SyntheticSections.cpp
> > +++ gnu/llvm/lld/ELF/SyntheticSections.cpp
> > @@ -1734,18 +1734,22 @@ void RelocationBaseSection::finalizeContents() {
> >  
> >  void DynamicReloc::finalize(Ctx &ctx, SymbolTableBaseSection *symt) {
> >    r_offset = getOffset();
> > -  if (ctx.arg.emachine == EM_SPARCV9 && type == R_SPARC_UA64 &&
> > -      needsDynSymIndex() && !sym->isPreemptible) {
> > -    if (r_offset % 8 != 0) {
> > +  bool wasSparcUA64 = ctx.arg.emachine == EM_SPARCV9 && type == R_SPARC_UA64;
> > +  if (wasSparcUA64) {
> > +    if (r_offset % 8 == 0) {
> > +      type = R_SPARC_64;
> > +    } else if (needsDynSymIndex() && !sym->isPreemptible) {
> >        Err(ctx) << "R_SPARC_UA64 relocation at offset " << r_offset
> >                 << " against non-preemptible symbol " << sym
> >                 << " is not 8-byte aligned";
> > -    } else {
> > -      type = ctx.target->relativeRel;
> > -      isAgainstSymbol = false;
> > -      expr = R_ABS;
> >      }
> >    }
> > +  if (wasSparcUA64 && type == R_SPARC_64 && needsDynSymIndex() &&
> > +      !sym->isPreemptible) {
> > +    type = ctx.target->relativeRel;
> > +    isAgainstSymbol = false;
> > +    expr = R_ABS;
> > +  }
> >    r_sym = getSymIndex(symt);
> >    addend = computeAddend(ctx);
> >    isFinal = true; // Catch errors
> > 
> > 
> > -- 
> > wbr, Kirill
> > 

-- 
wbr, Kirill