Bug 577896 – Qt5: incorrect CPU feature detection with -march=native?

• Status: RESOLVED TEST-REQUEST
• Product: Gentoo Linux

[Description Oleh 2016-03-21 04:40:51 UTC]

on a certain CPU's (currently, it's intel 4xxx) applications that compiled with qt5 exhibit runtime (start) failure due to "Incompatible processor" (in Actual Results)





Reproducible: Always

Steps to Reproduce:
1. USE="qt5 -qt4" emerge qpdfview
2. run qpdfview in terminal
3. notice a runtime problem as in 'Actual Results'
Actual Results:  
Incompatible processor. This Qt build requires the following features:
rtm
Aborted. Incompatible processor: missing feature 0x400 - rtm.


This is same (or very close) behavior described in:

1. https://forums.gentoo.org/viewtopic-t-1035266.html
2. http://comments.gmane.org/gmane.comp.kde.devel.bugs/1653744
3. https://bugs.kde.org/show_bug.cgi?id=354931

march native gives rtm instruction is disabled:

LANG=C gcc -march=native -Q --help=target | grep rtm
-mrtm [disabled]

dev-qt/qtcore: 5.5.1-r1 used

[Comment 1 Oleh 2016-03-21 04:41:16 UTC]

Created attachment 428690 [details]
cpuinfo

[Comment 2 Oleh 2016-03-21 04:49:57 UTC]

http://code.qt.io/cgit/qt/qtbase.git/tree/src/corelib/tools/qsimd_p.h?id=fae33bfbe35f8d082b420ee09662ff60634cb355&h=5.4#n264

http://code.qt.io/cgit/qt/qtbase.git/tree/src/corelib/tools/qsimd.cpp?id=fae33bfbe35f8d082b420ee09662ff60634cb355&h=5.4#n499

[Comment 3 Oleh 2016-03-21 05:48:38 UTC]

this could be probably fixed with 5.6.0 release, they have changed how cpu instructions detected. It's not in portage tree yet.

http://code.qt.io/cgit/qt/qtbase.git/commit/src/corelib/tools/qsimd_p.h?h=v5.6.0&id=6a8251a89b6a61258498f4af1ba7b3d5b7f7096c

[Comment 4 Davide Pesavento (RETIRED) 2016-04-23 19:03:57 UTC]

5.6.0 is in tree now. Please test and report back.