Re: RISC-V ABI issue with ULEB128

[Peter Robinson]

On Tue, Jan 2, 2024 at 5:15 PM David Abdurachmanov
<david.abdurachmanov(a)gmail.com&gt; wrote:
>  On Tue, Jan 2, 2024 at 6:26 PM Peter Robinson <pbrobinson(a)gmail.com&gt; wrote:
>  >
>  > On Tue, Jan 2, 2024 at 2:05 PM David Abdurachmanov
>  > <david.abdurachmanov(a)gmail.com&gt; wrote:
>  > >
>  > > On Tue, Jan 2, 2024 at 3:54 PM Florian Weimer <fweimer(a)redhat.com&gt;
> wrote:
>  > > >
>  > > > * David Abdurachmanov:
>  > > >
>  > > > > On Tue, Jan 2, 2024 at 1:09 PM Richard W.M. Jones
> <rjones(a)redhat.com&gt; wrote:
>  > > > >>
>  > > > >>
>  > > > >> I'm not sure exactly the effect on RISC-V binaries, but I
> wanted to
>  > > > >> raise it here to get the attention of the Fedora toolchain team
> ...
>  > > > >>
>  > > > >> Here's the bug:
>  > > > >>
>  > > > >> https://sourceware.org/bugzilla/show_bug.cgi?id=31179
>  > > > >> RISC-V: The SET/ADD/SUB fix breaks ABI compatibility with 2.41
> objects
>  > > > >>
>  > > > >> It refers to this change in binutils 2.41:
>  > > > >>
>  > > > >>
> https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=73d931e560059a8...
>  > > > >>
>  > > > >> As far as I understand the issue (which is not too far) this
> mainly
>  > > > >> affects shipped *.o and *.a files (ie. static libraries and
> similar)
>  > > > >> which were compiled with binutils < 2.41, which either
> won't link
>  > > > >> correctly or will give a linker error when using GNU ld from
> binutils 2.41.
>  > > > >
>  > > > > Correction. This is broken in <= 2.41 (incl. the current stable
>  > > > > binutils release).
>  > > > >
>  > > > >>
>  > > > >> Unclear if it also affects *.so files (which would be a much
> more
>  > > > >> serious ABI break), and also if it affects most binaries or just
> a
>  > > > >> few.  I initially thought this only affected programs using 128
> bit
>  > > > >> ints, so didn't think it was too important, but after reading
> the
>  > > > >> commit I'm not sure that is really true.
>  > > > >
>  > > > > Nelson Chu committed (5 days ago) a change:
>  > > > >
>  > > > >
> https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=73d931e560059a8...
>  > > > >
>  > > > > This will accept whatever is produced by <= 2.41 and the final
> binary
>  > > > > will be correct. There is also a new ld flag (--check-uleb128) which
>  > > > > can produce a warning if it detects an issue.
>  > > > >
>  > > > > I plan/hope to use binutils 2.42 in Fedora/RISCV 40. That would
> happen
>  > > > > before I start mass rebuilding, and that should fix this.
>  > > >
>  > > > Cc:ing Nick and Siddhesh for awareness.
>  > > >
>  > > > The current plan is to use binutils 2.41 for the mass rebuild.
>  > >
>  > > In Fedora/RISCV we typically end up using the latest available
>  > > binutils. We are slightly different from upstream/normal Fedora.
>  >
>  > Which is fine when you're an out of mainline architecture but these
>  > sorts of things need to be resolved well and truly before any
>  > incorporation can happen.
>
>  100% true. We have plenty of stuff that isn't yet submitted to the
>  official dist-git. 
Is that delta easily viewable somewhere?

> I have been considering not going for 2.42 for Fedora 40, but we will
> do this again one more time (hopefully it's the last time, but you
> never know).
>
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