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List: kde-frameworks-devel
Subject: Re: Review Request 127968: kshareddatacache: Fix invalid use of & to avoid unaligned reads
From: Michael Pyne <mpyne () kde ! org>
Date: 2016-05-20 23:10:07
Message-ID: 20160520231007.15344.6030 () mimi ! kde ! org
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> On May 19, 2016, 11:17 p.m., Michael Pyne wrote:
> > This is an error upstream in the MurmurHash 1.0 aligned implementation (which \
> > still contains the error, see \
> > https://sites.google.com/site/murmurhash/MurmurHashAligned.cpp?attredirects=0 )
> > In our case KSharedDataCache will never pass an unaligned block into the hash \
> > function so 'align' was always 0 (and boolean false) anyways. So I concur with \
> > not bumping the cache version and agree with your patch. Thanks for taking a \
> > look!
>
> Fabian Vogt wrote:
> I didn't know this aligned implementation actually had an upstream, it's actually \
> fixed there, the latest source is on GitHub: \
> https://github.com/aappleby/smhasher/blob/master/src/MurmurHash1.cpp#L87
Ah, great news then. I'll have to update the URL in the KSharedDataCache sources then \
for posterity.
- Michael
-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
https://git.reviewboard.kde.org/r/127968/#review95630
-----------------------------------------------------------
On May 20, 2016, 8:08 a.m., Fabian Vogt wrote:
>
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/127968/
> -----------------------------------------------------------
>
> (Updated May 20, 2016, 8:08 a.m.)
>
>
> Review request for KDE Frameworks, David Faure and Michael Pyne.
>
>
> Repository: kcoreaddons
>
>
> Description
> -------
>
> That the & is wrong here is obvious:
> align can never be 2 inside the if condition as ```(2 & bool)``` is always false,
> yet the switch on align contains a case for 2.
> Instead it drops into the while loop for an 4-byte aligned pointer.
>
> This doesn't change the returned values on platforms where unaligned reads
> are permitted, so I didn't bump the version.
>
>
> Diffs
> -----
>
> src/lib/caching/kshareddatacache.cpp 50bbf64
>
> Diff: https://git.reviewboard.kde.org/r/127968/diff/
>
>
> Testing
> -------
>
> Ran make test, all passed.
>
>
> Thanks,
>
> Fabian Vogt
>
>
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This is an automatically generated e-mail. To reply, visit:
<a href="https://git.reviewboard.kde.org/r/127968/">https://git.reviewboard.kde.org/r/127968/</a>
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<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: \
10px;"> <p style="margin-top: 0;">On May 19th, 2016, 11:17 p.m. UTC, <b>Michael \
Pyne</b> wrote:</p> <blockquote style="margin-left: 1em; border-left: 2px solid \
#d0d0d0; padding-left: 10px;"> <pre style="white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;">This is an error upstream in the MurmurHash 1.0 aligned implementation \
(which still contains the error, see \
https://sites.google.com/site/murmurhash/MurmurHashAligned.cpp?attredirects=0 )
In our case KSharedDataCache will never pass an unaligned block into the hash \
function so 'align' was always 0 (and boolean false) anyways. So I concur \
with not bumping the cache version and agree with your patch. Thanks for taking a \
look!</pre> </blockquote>
<p>On May 20th, 2016, 6:51 a.m. UTC, <b>Fabian Vogt</b> wrote:</p>
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: \
10px;"> <pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: \
-pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;"><p style="padding: \
0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: inherit;">I \
didn't know this aligned implementation actually had an upstream, it's actually fixed \
there, the latest source is on GitHub: \
https://github.com/aappleby/smhasher/blob/master/src/MurmurHash1.cpp#L87</p></pre> \
</blockquote>
</blockquote>
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: \
-pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">Ah, great news then. \
I'll have to update the URL in the KSharedDataCache sources then for \
posterity.</pre> <br />
<p>- Michael</p>
<br />
<p>On May 20th, 2016, 8:08 a.m. UTC, Fabian Vogt wrote:</p>
<table bgcolor="#fefadf" width="100%" cellspacing="0" cellpadding="12" style="border: \
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<div>Review request for KDE Frameworks, David Faure and Michael Pyne.</div>
<div>By Fabian Vogt.</div>
<p style="color: grey;"><i>Updated May 20, 2016, 8:08 a.m.</i></p>
<div style="margin-top: 1.5em;">
<b style="color: #575012; font-size: 10pt;">Repository: </b>
kcoreaddons
</div>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" \
style="border: 1px solid #b8b5a0"> <tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">That the & is wrong here is obvious: align can \
never be 2 inside the if condition as <code style="text-rendering: inherit;color: \
#4444cc;padding: 0;white-space: normal;margin: 0;line-height: inherit;">(2 & \
bool)</code> is always false, yet the switch on align contains a case for 2.
Instead it drops into the while loop for an 4-byte aligned pointer.</p>
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">This doesn't change the returned values on platforms \
where unaligned reads are permitted, so I didn't bump the version.</p></pre>
</td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Testing </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" style="border: \
1px solid #b8b5a0"> <tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">Ran make test, all passed.</p></pre> </td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
<ul style="margin-left: 3em; padding-left: 0;">
<li>src/lib/caching/kshareddatacache.cpp <span style="color: \
grey">(50bbf64)</span></li>
</ul>
<p><a href="https://git.reviewboard.kde.org/r/127968/diff/" style="margin-left: \
3em;">View Diff</a></p>
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