On 11/6/18 6:35 PM, Andres Freund wrote:
On 2018-11-06 18:24:55 +0100, Tomas Vondra wrote:
I've recently updated to Fedora 28, and in that environment I get quite a
few new valgrind issues (see the attached log).
Essentially, all the reports start with either
==5971== Invalid read of size 32
==5971== at 0x5957EB1: __wcsnlen_avx2 (in /usr/lib64/libc-2.27.so)
==5971== by 0x589E871: wcsrtombs (in /usr/lib64/libc-2.27.so)
==5971== by 0x5834000: wcstombs (in /usr/lib64/libc-2.27.so)
==5971== by 0x97DD82: wchar2char (pg_locale.c:1641)
I think this isn't actually a bug, just a missing suppression. The avx2
code uses instructions to scan for 0 bytes in multiple bytes at the same
time. Therefore it can encounter a byte marked as undefined, even if it
never actually uses that value.
OK, my thoughts exactly.
or
==5971== Conditional jump or move depends on uninitialised value(s)
==5971== at 0x5822123: __gconv_transform_internal_utf8 (in
/usr/lib64/libc-2.27.so)
==5971== by 0x589E8A4: wcsrtombs (in /usr/lib64/libc-2.27.so)
==5971== by 0x5834000: wcstombs (in /usr/lib64/libc-2.27.so)
==5971== by 0x97DD82: wchar2char (pg_locale.c:1641)
or some other combination of that. In all cases the call stack is
wchar2char > wcstombs > wcsrtombs > something
I think I came to the same conclusion here, but I'm not quite sure.
Looking at gconv code at [1], it seems it's reading the data as int32
values and using shifts to extract individual bytes. I'm pretty sure
this confuses valgrind so it thinks it's accessing all the bytes.
[1]
https://sourceware.org/git/?p=glibc.git;a=blob;f=iconv/gconv_simple.c;h=506c92caf228d61f92986c39a2ddf9c0a134b4c0;hb=HEAD
FWIW, I've supressed these on my valgrind animal a while ago.
OK, I propose to add these suppressions into the current list.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
