[Bug bootstrap/115284] [15 regression] SEGV in check_format_arg on Solaris/SPARC

[hp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115284

--- Comment #12 from Hans-Peter Nilsson <hp at gcc dot gnu.org> ---
(In reply to ro@CeBiTec.Uni-Bielefeld.DE from comment #11)
> > --- Comment #10 from Hans-Peter Nilsson <hp at gcc dot gnu.org> ---

> >> The failure is even earlier here: in a sparc64-unknown-linux-gnu
> >> bootstrap, building a libstdc++ .gch file in stage 2 breaks:
> >
> > Great, thanks!  That means that tricking my pc into believing it's a sparc by
> > means of using the binfmt machinery that Jeff mentioned in the thread where I
> > mentioned the revert on gcc-patches, would work.  (I don't have the details and
> > don't remember if I'd actually tried it, certainly not recently; I just know
> > about the concept.)
> 
> I can't help but wonder if this wouldn't be a total waste of your time:
> considering what the qemu wiki docments for SPARC support
> 
> https://wiki.qemu.org/Documentation/Platforms/SPARC
> 
> seems not too encouraging for 64-bit systems.

Thanks for the warning, but I'm confused as it doesn't look too bad to me; for
example the status field for SPARC64 says "working" at least for non-historic
qemu versions.  What am I missing?  Are you thinking of something specific
there?

> When I think about what
> it took myself to get recent macOS working on qemu-kvm (although the
> procedure is resonably well documented, with firmware and all
> available), I'd consider such an attempt a positive nightmare.

Also, I wouldn't be using qemu-system-sparc64 IIUC: with the binfmt trick I'd
be using qemu-user.

That "experience" (assuming success) would also lead to a template or identical
solution for other targets, which is the most interesting part.  The cfarm is
nice to have, but the machines are a bit crowded.

> When all it takes for you to either get your ssh client working to
> access a ready-made and not too slow SPARC system (or in the worst case,
> build OpenSSH from source), I know which route I'd take ;-)

A different nightmare, leading to a nightmare of chasing a bootstrap failure on
a system I'm not familiar with (referring to solaris on the cfarm machine).

> > What's not so great is that the described reproducer is a bootstrap, so the
> > debug situation is unpleasant.  The first step I'd do, would be to just do a
> > cross-build (or native --disable-bootstrap) and just run the testsuite
> > before/after the patch-set (or just 933ab59c59bdc1) and see if the problem
> > manifests there.

> I've tried that now on both
> 
> * sparc-sun-solaris2.11 (c and c++ only): no additional testsuite
>   failures are apparent there, which is not too astonishing given that
>   the bootstrap failure occurs in stage 3, suggesting a mis-compiled
>   stage 2 cc1plus, and

Oh, too bad.  Thanks for doing that!

> * sparc64-unknown-linux-gnu (again, c and c++ only): there are testsuite
>   failures all over the place, but I'd have to perform another bootstrap
>   with your patches removed to make an exact comparison.

Hm, the part where you compare results against a baseline is pretty central.

One the one hand, when it doesn't manifest for sparc64-solaris just through the
testsuite, the odds are against it manifesting that simple for sparc64-linux. 
On the other hand, an existing reproducer is so much easier to handle.  Thank
you and thanks in advance for the last step!