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Date: Fri, 10 Jan 2020 11:22:14 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Cc: Patrick Oppenlander <patrick.oppenlander@...il.com>
Subject: Re: another armv7-m exception handling problem
* Rich Felker <dalias@...c.org> [2019-10-21 15:29:37 -0400]:
> On Mon, Oct 21, 2019 at 09:08:57PM +0200, Szabolcs Nagy wrote:
> > * Rich Felker <dalias@...c.org> [2019-10-21 15:03:18 -0400]:
> > > On Mon, Oct 21, 2019 at 08:09:56PM +0200, Szabolcs Nagy wrote:
> > > > * Patrick Oppenlander <patrick.oppenlander@...il.com> [2019-10-21 15:43:40 +1100]:
> > > > > Not sure if this is a musl, gcc or ld bug.
> > > > >
> > > > > Running gcc-8.3.0 musl 1.1.24 static pie.
> > > >
> > > > providing binutils version number is useful if there is
> > > > a chance that it's an ld bug.
> > > >
> > > > this seems to be
> > > > https://sourceware.org/bugzilla/show_bug.cgi?id=22269
> > > >
> > > > which was supposed to be fixed by
> > > > https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=95b03e4ad68e7a90f5096b47df595636344b783a
> > > >
> > > > but apperently there are still missing cases.
> > > > (it does not help that the ld test for this bug
> > > > greps for R_*_NONE dynrelocs but not R_*_RELATIVE
> > > > which i is just as bad for undef weak syms in pie)
> > > > i added a note to the bug.
> > > >
> > > > if you add __attribute__((visibility("hidden")))
> > > > to the example given by Rich then it works, the
> > > > bug only affects static pie linking.
> > >
> > > That's really weird. How does it end up having an outstanding
> > > *relative* relocation when it's not defined locally? I could
> > > understand having a bogus outstanding symbolic one, but relative makes
> > > no sense and suggests ld is doing something very wrong...
> >
> > i'd guess it creates a relative reloc for every
> > got entry that stores some symbol's address
> > which is known to be local, which makes sense,
> > except for undefined weak symbols which should
> > have fixed 0 address.
> >
> > and i'd guess there is some logic that special
> > cases local undef weak in pic so hidden works,
> > and that check should be extended to cover the
> > static pie case.
>
> In 2.33.1, the offending code (creating the bad relative relocation)
> is at line 11637. It's possible some earlier code path leading to it
> is wrong, around line 11515 or so, but I think there just needs to be
> an extra else path before this one that covers undefined/undefweak.
fyi i have a patch now, hopefully will be included into binutils 2.34
https://sourceware.org/ml/binutils/2020-01/msg00096.html
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