Ok, I have been trying to track this bug down for weeks and spent quite a lot of time on it. I am now pretty much sure that this is a bug within gcc even though it's quite hard to prove. So before I sum it up again here, first two links to my original bug reports over at the Gentoo and Xorg bugzilla:
https://bugs.gentoo.org/show_bug.cgi?id=127608 https://bugs.freedesktop.org/show_bug.cgi?id=6533 When the Xorg server package is being compiled with anything above -O0, only the first switch to the VT works. Every other switch results in a black screen, even though I am able to enter commands blindly. After Xorg has been stopped, sometimes the VT is being restored, even though some VTs are left in a garbled state like some kind of video memory corruption occured. The most interesting part is: this only happens with gcc 4.1 and above. If I compile the Xorg server with gcc 3.4.5 or 4.0.3, everything works just fine. I have tried 4.1.1 and 4.2 snapshots a few days ago but the problem remained. What's also note worthy: just replacing the Xorg binary with for example an -O0 compiled one, fixes the problem too. So no matter what wrong code is being produced, it's in Xorg server binary. I have tried to nail the bug down with to some specific CFLAG but I had no luck. Tried the following so far one by one: -march=athlon64 -mtune=athlon64 -O1 -pipe -fno-defer-pop -fno-delayed-branch -fno-guess-branch-probability -fno-cprop-registers -fno-loop-optimize -fno-if-conversion -fno-if-conversion2 -fno-tree-ccp -fno-tree-dce -fno-tree-dominator-opts -fno-tree-dse -fno-tree-ter -fno-tree-lrs -fno-tree-sra -fno-tree-copyrename -fno-tree-fre -fno-tree-ch -fno-merge-constants -fno-tree-loop-optimize -fno-omit-frame-pointer -fno-tree-sink -fno-tree-copy-prop -fno-tree-vect-loop-version -fno-tree-salias -fno-default-inline -fno-inline -fno-early-inlining -fno-peephole -fno-peephole2 -fno-move-loop-invariants -fno-ivopts -fno-schedule-insns -fno-strength-reduce -fno-align-functions -fno-align-jumps -fno-align-labels -fno-align-loops I also tried to debug the problem with gdb but I it's more like looking for the needle in the haystack if you don't know what you are looking for. My system is a pure 64bit Gentoo system, everything compiled with gcc 4.1.0 and just -march=athlon64 -mtune=athlon64 -O2 -pipe -ftracer -fweb -frename-registers as CFLAGS. Running glibc 2.4 and kernel 2.6.16. If you need any more detailed informations, help or alike, I will gladly help. It's just that I am currently stuck and don't know what else I could try to find the needle. -- Summary: gcc 4.1.x/4.2 produces wrong code for Xorg server (1.0.2, modular) Product: gcc Version: 4.1.0 Status: UNCONFIRMED Severity: major Priority: P3 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: ua_bugz_gcc at mortal-soul dot de http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27152
