Date: Fri, 22 Jan 2021 13:31:27 -0500 From: Rich Felker <dalias@...c.org> To: 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 03:19:22PM -0300, Raoni Fassina Firmino wrote: > 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. Is there a reason it's backtracing rather than just looking at the interrupted context (pointed to by the third argument to the signal handler)? Rich
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