[Bug string/20327] New: POWER8 strcasecmp returns incorrect result

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=20327

            Bug ID: 20327
           Summary: POWER8 strcasecmp returns incorrect result
           Product: glibc
           Version: 2.24
            Status: NEW
          Severity: normal
          Priority: P2
         Component: string
          Assignee: unassigned at sourceware dot org
          Reporter: fweimer at redhat dot com
                CC: raji at linux dot vnet.ibm.com
  Target Milestone: ---
            Target: ppc64le. ppc64

We have received a report of a build failure of krb5

  https://bugzilla.redhat.com/show_bug.cgi?id=1351737

induced by this commit:

commit c8376f3e07602aaef9cb843bb73cb5f2b860634a
Author: raji <raji@oc4354787705.ibm.com>
Date:   Tue Jun 14 14:51:16 2016 +0530

    powerpc: strcasecmp/strncasecmp optmization for power8

    This implementation utilizes vectors to improve performance
    compared to current byte by byte implementation for POWER7.
    The performance improvement is upto 4x.  This patch is tested
    on powerpc64 and powerpc64le.

I tried to reproduce this outside the krb5 build.  It does not seem to be a
simple alignment issue.

At the start of strcasecmp, the arguments are:

(gdb) print (char *)$r3
$73 = 0x3fffb7e11fd8 "des3-cbc-sha1-kd"
(gdb) print (char *)$r4
$74 = 0x4e1b02f4 "des3-cbc-sha1-kd"

The surrounding memory looks like this:

0x3fffb7e11fc8: 100 'd' 101 'e' 115 's' 51 '3'  45 '-'  104 'h' 109 'm' 97 'a'
0x3fffb7e11fd0: 99 'c'  45 '-'  115 's' 104 'h' 97 'a'  49 '1'  0 '\000'       
0 '\000'
0x3fffb7e11fd8: 100 'd' 101 'e' 115 's' 51 '3'  45 '-'  99 'c'  98 'b'  99 'c'
0x3fffb7e11fe0: 45 '-'  115 's' 104 'h' 97 'a'  49 '1'  45 '-'  107 'k' 100 'd'
0x3fffb7e11fe8: 0 '\000'        0 '\000'        0 '\000'        0 '\000'       
0 '\000'        0 '
\000'   0 '\000'        0 '\000'
0x3fffb7e11ff0: 84 'T'  114 'r' 105 'i' 112 'p' 108 'l' 101 'e' 32 ' '  68 'D'

0x4e1b02e4:     105 'i' 110 'n' 115 's' 0 '\000'        33 '!'  0 '\000'       
0 '\000'        0 '
\000'
0x4e1b02ec:     0 '\000'        0 '\000'        0 '\000'        0 '\000'       
97 'a'  101 'e' 115
 's'    0 '\000'
0x4e1b02f4:     100 'd' 101 'e' 115 's' 51 '3'  45 '-'  99 'c'  98 'b'  99 'c'
0x4e1b02fc:     45 '-'  115 's' 104 'h' 97 'a'  49 '1'  45 '-'  107 'k' 100 'd'
0x4e1b0304:     0 '\000'        57 '9'  54 '6'  0 '\000'        49 '1'  0
'\000'        0 '\000'
     0 '\000'
0x4e1b030c:     0 '\000'        0 '\000'        0 '\000'        0 '\000'       
18 '\022'       96
'`'     -54 '\312'      -86 '\252'

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