Chris Lalancette wrote: > Avi Kivity wrote: > >> Now it uses %rsi instead of %esi, and any junk in the upper bits will >> cause the ja to be taken. >> >> We need to get a reduced testcase to the gcc folks, this is a serious >> bug. Any changes in the code to work around this would be fragile. >> >> > > Avi, > I've now filed a bug in the upstream gcc database: > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36040 > > And I came up with a reduced test case, available here: > > http://people.redhat.com/clalance/rsi-test-case.tar.bz2 > > If I compile the code in the above and look at the disassembly, it shows the > problem; however, I can't reproduce the bug by actually running the code. I > suspect the %rsi register is always 0 when we start in this userland code, so > I > never run into the bogus ja, but I just thought I'd mention it. > >
Hmm, looking back at the dump: > 1811: 8d 86 00 00 ff 3f lea 0x3fff0000(%rsi),%eax > 1817: 83 f8 03 cmp $0x3,%eax > 181a: 0f 87 e2 01 00 00 ja 1a02 <svm_set_msr+0x27f> So while gcc is using %rsi, it loads the result back into %eax, which has the effect of dropping back into 32-bits. So looks like gcc was right here. Sorry for spreading confusion and apologies to gcc. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
