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Date: Fri, 22 Jan 2021 15:19:22 -0300
From: Raoni Fassina Firmino <>
To: Rich Felker <>
Cc: Florian Weimer <>,,,,
        Nicholas Piggin <>, Alan Modra <>
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.

Raoni Fassina

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