Date: Tue, 23 Jan 2007 23:59:04 +0100 From: Tijl Coosemans <tijl@ulyssis.org> To: freebsd-emulation@freebsd.org Cc: Jung-uk Kim <jkim@freebsd.org> Subject: Re: linuxolator: tls_test results amd64 Message-ID: <200701232359.07434.tijl@ulyssis.org> In-Reply-To: <200701232343.47316.tijl@ulyssis.org> References: <790a9fff0701211041j1176d00gd6dd75d0989cf4ec@mail.gmail.com> <200701231555.57521.jkim@FreeBSD.org> <200701232343.47316.tijl@ulyssis.org>
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On Tuesday 23 January 2007 23:43, Tijl Coosemans wrote: > On Tuesday 23 January 2007 21:55, Jung-uk Kim wrote: > > On Tuesday 23 January 2007 03:13 pm, Tijl Coosemans wrote: > > > On Tuesday 23 January 2007 20:00, Jung-uk Kim wrote: > > > > Second problem is MSR_KGSBASE is scrubbed by something during > > > > context switch, i.e., it becomes 0 some times. > > > > Saved pcb_gsbase seems always correct. MSR_KGSBASE is not, which is > > supposedly swapped with MSR_GSBASE via swapgs. Maybe I am confused, > > or maybe my CPU is too old (it's C0 stepping and I know there are > > some segmentation issues with the revision) but that's what I see. I > > need more time for testing (or resting?). > > Ok, I understand why pcb_gsbase is always correct. It is never written > to except for cpu_set_user_tls, i386_set_gsbase and set_thread_area. > cpu_switch only reads from it to restore gsbase. At least, that's what > cpu_switch does in case of 64 bit programs, not 32 bit it seems. Why > is that? Why is there a jmp on line 186 in sys/amd64/amd64/cpu_switch.S? This doesn't explain why gsbase becomes 0 by the way. I still think that's because glibc does "mov index,%gs" after calling set_thread_area.
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