linux-kernel - Re: [PATCH v2 1/6] powerpc/perf: Define big-endian version of perf_mem_data

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 13 Mar 2017 16:45:51 +0530
From:   Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mpe@...erman.id.au, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org,
        Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Wang Nan <wangnan0@...wei.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v2 1/6] powerpc/perf: Define big-endian version of
 perf_mem_data_src



On Tuesday 07 March 2017 03:53 PM, Peter Zijlstra wrote:
> On Tue, Mar 07, 2017 at 03:28:17PM +0530, Madhavan Srinivasan wrote:
>>
>> On Monday 06 March 2017 04:52 PM, Peter Zijlstra wrote:
>>> On Mon, Mar 06, 2017 at 04:13:08PM +0530, Madhavan Srinivasan wrote:
>>>> From: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
>>>>
>>>> perf_mem_data_src is an union that is initialized via the ->val field
>>>> and accessed via the bitmap fields. For this to work on big endian
>>>> platforms, we also need a big-endian represenation of perf_mem_data_src.
>>> Doesn't this break interpreting the data on a different endian machine?
>> IIUC, we will need this patch to not to break the interpreting data
>> on a different endian machine. Data collected from power8 LE/BE
>> guests with this patchset applied. Kindly correct me if I missed
>> your question here.
> So your patch adds compile time bitfield differences. My worry was that
> there was no dynamic conversion routine in the tools (it has for a lot
> of other places).
>
> This yields two questions:
>
>   - are these two static layouts identical? (seeing that you illustrate
>     cross-endian things working this seems likely).
>
>   - should you not have fixed this in the tool only? This patch
>     effectively breaks ABI on big-endian architectures.

IIUC, we are the first BE user for this feature
(Kindly correct me if I am wrong), so technically we
are not breaking ABI here :) .  But let me also look  at
the dynamic conversion part.

Maddy

>