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* Klaus S. Madsen <ksm@hjernemadsen.org> wrote: > > > 524 int r; > > > 525 #ifdef __PIC__ > > > 526 asm volatile ( > > > 527 "pushl %%ebx\n\t" > > > 528 "movl %2, %%ebx\n\t" > > > 529 "int $0x80\n\t" > > > 530 "popl %%ebx" > > > (gdb) bt > > > #0 0xb7facf4a in run_vm86 () at lrmi.c:526 > > > #1 0xb7fad61b in LRMI_int (i=16, r=0xbffca670) at lrmi.c:844 > > > #2 0x0804acfc in do_vbe_service (AX=20227, BX=0, regs=0xbffca670) > > > at vbetool/vbetool.c:158 > > > #3 0x0804af7e in __get_mode () at vbetool/vbetool.c:453 > > > #4 0x0804a30f in s2ram_hacks () at s2ram-x86.c:268 > > > #5 0x0804954f in main (argc=1, argv=0x0) at s2ram-main.c:92 > > > > > > I have tried to bisect the problem, and it fingered the following > > > commit: > > > > > > commit 82bc03fc158e28c90d7ed9919410776039cb4e14 > > > Author: Ingo Molnar <mingo@elte.hu> > > > > > > x86: add PWT to NOCACHE flags > > > > > > Reverting this commit in the bisected tree (by executing git show > > > 82bc03fc158e28c90d7ed9919410776039cb4e14 | patch -R -p1), makes the > > > segfault go away. I've run make clean between each kernel compile, to > > > be sure the tree was correctly compiled. > > > > thanks for tracking this down. It would be nice to figure out why this > > change made a difference. Perhaps VM86 mode has some restrictions in > > what type of pagetables it can operate in - and the CPU just refuses to > > properly emulate those 16-bit instructions? (this would be very weird). > > We are trying to execute 16-bit BIOS code here, right? > > > > which instruction is the segfault coming from - the int $0x80? So in > > vm86 mode we generated a #GPF which shows up as a SIGSEGV? > I must say, that I don't quite understand why gdb fingers the "asm > volatile" line and not one of the assembly lines, when reporting the > segfault. But I'm not really well versed in lowlevel gdb use, so if you > could give me a about how I get gdb to disassemble the code at the > instruction pointer, I'll return with the result. typing 'disassemble' should do the trick. If you have a specific address outside of the current instruction pointer, then doing disassembly on a range: disassemble 0xb7facf4a 0xb7facf8a should work too. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | |||||||||
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