linux-kernel - Re: [PATCHSET] saner elf compat

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Message-ID: <20201222213835.GU3579531@ZenIV.linux.org.uk>
Date:   Tue, 22 Dec 2020 21:38:35 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     "Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        linux-mips@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCHSET] saner elf compat

On Tue, Dec 22, 2020 at 08:04:31PM +0000, Al Viro wrote:

> FWIW, on debian/mips64el (both stretch and buster) the test fails with the
> distro kernels (4.9- and 4.19-based) as well as with 5.10-rc1 and
> 5.10-rc1+that series, all in the same way:
> [Current thread is 1 (LWP 4154)]
> (gdb) p/x foo
> Cannot find thread-local storage for LWP 4154, executable file <pathname>
> Cannot find thread-local variables on this target
> 
> buster has libc6-2.28, so that should be fine for the test in question
> (libthread_db definitely recent enough).  That was n32 gdb; considering
> how much time it had taken to build that sucker I hadn't tried o32
> yet.
> 
> Note that it's not just with native coredumps - gcore-produced ones give
> the same result.  That was gdb from binutils-gdb.git; I'm not familiar
> with gdb guts to start debugging it, so if you have any suggestions
> in that direction that do not include a full rebuild...  In any case,
> I won't get around to that until the next week.
> 
> Incidentally, build time is bloody awful - 3 days, with qemu-3.1 on
> 3.5GHz amd64 host, all spent pretty much entirely in userland (both
> from guest and host POV).  g++-8 is atrociously slow...
> 
> That said, I don't see what in that series could possibly mess the
> things up for tls, while leaving the registers working; the only
> thing that realistically might've been fucked up is prstatus layout
> (and possibly size), and that would've screwed the registers as
> well.

... and it smells like the damn thing needs n32 debug info from libthread_db.so
and/or libpthread.so.  Which is not packaged by debian libc6 mips64el build.
Sorry, any debugging of that crap is going to happen in January ;-/