linux-kernel - Re: [PATCH] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel

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Message-ID: <20210820181201.GT1583@gate.crashing.org>
Date:   Fri, 20 Aug 2021 13:12:01 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Paul Mackerras <paulus@...ba.org>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel_thread

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@...roup.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