linux-kernel - Re: [RFC PATCH 7/7 v1]powerpc: Deliver SEGV signal on protection key violation.

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Date:   Fri, 16 Jun 2017 12:15:37 -0700
From:   Ram Pai <linuxram@...ibm.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        dave.hansen@...el.com, paulus@...ba.org,
        aneesh.kumar@...ux.vnet.ibm.com
Subject: Re: [RFC PATCH 7/7 v1]powerpc: Deliver SEGV signal on protection key
 violation.

On Fri, Jun 16, 2017 at 08:33:01PM +1000, Benjamin Herrenschmidt wrote:
> On Fri, 2017-06-16 at 14:50 +0530, Anshuman Khandual wrote:
> > On 06/06/2017 06:35 AM, Ram Pai wrote:
> > > The value of the AMR register at the time of the exception
> > > is made available in gp_regs[PT_AMR] of the siginfo.
> > 
> > But its already available there in uctxt->uc_mcontext.regs->amr
> > while inside the signal delivery context in the user space. The
> > pt_regs already got updated with new AMR register. Then why we
> > need gp_regs to also contain AMR as well ?
> 
> Also changing gp_regs layout/size is a major ABI issue...

Ben,
	
gp_regs size is not changed, nor is the layout. A unused field in
the gp_regs is used to fill in the AMR contents. Old binaries will not
be knowing about this unused field, and hence should not break.

New binaries can leverage this already existing but newly defined
field; to read the contents of AMR.

Is it still a concern?
RP

> 
> Ben.

-- 
Ram Pai