linux-kernel - Re: [PATCH 1/3] powerpc: Emulation support for load/store instructions on LE

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Message-Id: <581C1D32.50108@linux.vnet.ibm.com>
Date:   Fri, 4 Nov 2016 11:01:30 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
To:     Andrew Donnellan <andrew.donnellan@....ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     chris@...troguy.com, aneesh.kumar@...ux.vnet.ibm.com,
        ast@...nel.org, linux-kernel@...r.kernel.org, oss@...error.net,
        paul.gortmaker@...driver.com, duwe@....de,
        Anton Blanchard <anton@...ba.org>,
        lsorense@...lub.uwaterloo.ca, bauerman@...ux.vnet.ibm.com,
        oohall@...il.com, naveen.n.rao@...ux.vnet.ibm.com,
        linuxppc-dev@...ts.ozlabs.org, paulus@...ba.org,
        viro@...iv.linux.org.uk,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/3] powerpc: Emulation support for load/store
 instructions on LE



On Friday 04 November 2016 07:37 AM, Andrew Donnellan wrote:
> On 03/11/16 21:27, Ravi Bangoria wrote:
>> Yes, kernel-space hw-breakpoint feature is broken on LE without this.
>
> Is there any actual user-visible feature that depends on this, or is this solely for debugging and development purposes?
>
> It would of course be *nice* to have it in stable trees (particularly so we pick it up in distros) but I'm not convinced that enabling HW breakpoints on a platform where it has *never* worked qualifies as an "actual bug".
>
> (BTW many thanks for fixing this - I had a shot at it late last year but never quite got there!)

Thanks Andrew,

kprobe, uprobe, hw-breakpoint and xmon are the only user of emulate_step.

Kprobe / uprobe single-steps instruction if they can't emulate it, so there
is no problem with them. As I mention, hw-breakpoint is broken. However
I'm not sure about xmon, I need to check that.

So yes, there is no user-visible feature that depends on this.

-Ravi