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Message-ID: <20210122181922.pcxyomeg5xcf2umu@work-tp>
Date: Fri, 22 Jan 2021 15:19:22 -0300
From: Raoni Fassina Firmino <raoni@...ux.ibm.com>
To: Rich Felker <dalias@...c.org>
Cc: Florian Weimer <fweimer@...hat.com>, musl@...ts.openwall.com,
libc-alpha@...rceware.org, linuxppc-dev@...ts.ozlabs.org,
Nicholas Piggin <npiggin@...il.com>, Alan Modra <amodra@...il.com>
Subject: Re: Re: [PATCH v2] powerpc/64/signal: balance return
predictor stack in signal trampoline
On Fri, Jan 22, 2021 at 09:44:05AM -0500, Rich Felker wrote:
> Maybe I'm missing something but I don't see how this would break musl;
> we just inspect the PC in the mcontext, which I don't see any changes
> to and which should still point to the next instruction of the
> interrupted context. I don't have a test environment though so I'll
> have to wait for feedback from ppc users to be sure. Are there any
> further details on how it's breaking glibc?
For glibc, backtrace() compares the return-address from each stack frame
to the value of `__kernel_sigtramp_rt64` to identify the frame with the
mcontext information, but now the return-address is not the start of the
routine, but the middle of it, so it fails to catch this special frame.
o/
Raoni Fassina
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