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Date:   Fri, 20 Aug 2021 13:12:01 -0500
From:   Segher Boessenkool <segher@kernel.crashing.org>
To:     Michael Ellerman <mpe@ellerman.id.au>
Cc:     Paul Mackerras <paulus@samba.org>, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
Message-ID: <20210820181201.GT1583@gate.crashing.org>
References: <91b1d242525307ceceec7ef6e832bfbacdd4501b.1629436472.git.christophe.leroy@csgroup.eu> <871r6oe2i8.fsf@mpe.ellerman.id.au> <20210820171845.GS1583@gate.crashing.org>
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On Fri, Aug 20, 2021 at 12:18:45PM -0500, Segher Boessenkool wrote:
> On Fri, Aug 20, 2021 at 10:15:11PM +1000, Michael Ellerman wrote:
> > Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> > > Copied from commit 89bbe4c798bc ("powerpc/64: indirect function call
> > > use bctrl rather than blrl in ret_from_kernel_thread")
> > >
> > > blrl is not recommended to use as an indirect function call, as it may
> > > corrupt the link stack predictor.
> > 
> > Do we know if any 32-bit CPUs have a link stack predictor or similar?
> 
> 74xx do.

7450 and later, that is.  Will I ever get that right, sigh.


Segher