From: Mark Kettenis <mark.kettenis@xs4all.nl>
Subject: Re: ld.so/sparc64: fix UA64 relocation mask selection and byte order
To: Kirill A. Korinsky <kirill@korins.ky>
Cc: tech@openbsd.org
Date: Thu, 09 Jul 2026 17:01:34 +0200

> 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?


> 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
>