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From: "fw at deneb dot enyo.de" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug dynamic-link/25680] ifuncmain9picstatic and ifuncmain9picstatic
 crash in IFUNC resolver due to stack canary
 (--enable-stack-protector=all)
Date: Sun, 15 Mar 2020 12:25:58 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D25680

--- Comment #4 from Florian Weimer <fw at deneb dot enyo.de> ---
(In reply to Sergei Trofimovich from comment #3)
> Does it mean --enable-stack-protector=3Dall is not really a supported opt=
ion
> for glibc? If' it's not I can hack a patch that complains loudly about the
> option being experimental.

It is supported in the sense that it is there and you can build glibc with =
it,
but some edge cases in the test suite have not been covered. (At this time,=
 I'm
not sure if this is a test bug or a bug in the static initialization sequen=
ce,
though.)

> My main worry is that resolver in ifuncmain9picstatic's source code only
> happens to be a part of glibc. It could have been an external program. Any
> external program might decide to enable -fstack-protector-all and will get
> non-working resolver as a result. Is there a doc that describes this and
> other limitations imposed on IFUNC resolves by glibc? I wonder what else =
we
> break by accident.

It's a valid concern. We probably have to reorder the initialization sequen=
ce
because on some architecture (notably powerpc as of commit
67385a01d229751569b6aac067ffdcd813a15d7a ("powerpc: Add hwcap/hwcap2/platfo=
rm
data to TCB."), IFUNC resolvers are expected to access the TCB to choose the
appropriate implementation.

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