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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-9707) Fix register lists for crc32c inline assembly
Date Wed, 10 Jul 2013 13:07:49 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-9707?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13704523#comment-13704523
] 

Kihwal Lee commented on HADOOP-9707:
------------------------------------

Sorry I thought I posted +1 almong with my findings yesterday. 

+1 for the patch. 

I also looked at the documentation Brian quoteded. I tried many things to make compilers generate
a problematic RTL, but was unsuccessful until the loop unrolling was enabled. I could clearly
see the defect in there. 

Thanks for finding and providing the fix. 

                
> Fix register lists for crc32c inline assembly
> ---------------------------------------------
>
>                 Key: HADOOP-9707
>                 URL: https://issues.apache.org/jira/browse/HADOOP-9707
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: util
>    Affects Versions: 3.0.0, 2.1.0-beta
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Minor
>         Attachments: hadoop-9707.txt
>
>
> The inline assembly used for the crc32 instructions has an incorrect clobber list: the
computed CRC values are "in-out" variables and thus need to use the "matching constraint"
syntax in the clobber list.
> This doesn't seem to cause a problem now in Hadoop, but may break in a different compiler
version which allocates registers differently, or may break when the same code is used in
another context.

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