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Date: Wed, 8 Jul 2020 18:53:31 -0500
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: Failure to build librseq on ppc
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Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
 Boqun Feng <boqun.feng@gmail.com>,
 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
 Michael Jeanson <mjeanson@efficios.com>
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

Hi!

On Wed, Jul 08, 2020 at 10:27:27PM +1000, Michael Ellerman wrote:
> Segher Boessenkool <segher@kernel.crashing.org> writes:
> > You'll have to show the actual failing machine code, and with enough
> > context that we can relate this to the source code.
> >
> > -save-temps helps, or use -S instead of -c, etc.
> 
> Attached below.

Thanks!

> I think that's from:
> 
> #define LOAD_WORD       "ld "
> 
> #define RSEQ_ASM_OP_CMPEQ(var, expect, label)                                   \
>                 LOAD_WORD "%%r17, %[" __rseq_str(var) "]\n\t"                   \

The way this hardcodes r17 *will* break, btw.  The compiler will not
likely want to use r17 as long as your code (after inlining etc.!) stays
small, but there is Murphy's law.

Anyway...  something in rseq_str is wrong, missing %X<n>.  This may
have to do with the abuse of inline asm here, making a fix harder :-(


Segher