Frederik Deweerdt wrote: > On Thu, Dec 21, 2006 at 11:22:05AM -0800, Jeremy Fitzhardinge wrote: > >> Frederik Deweerdt wrote: >> >>> Following the i386 pda patches, it's not possible to set gs or fs value >>> from gdb anymore. The following patch restores the old behaviour of >>> getting and setting thread.gs of thread.fs respectively. >>> Here's a gdb session *before* the patch: >>> (gdb) info reg >>> [...] >>> fs 0x33 51 >>> gs 0x33 51 >>> (gdb) set $fs=0xffff >>> (gdb) info reg >>> [...] >>> fs 0x33 51 >>> gs 0x33 51 >>> (gdb) set $gs=0xffffffff >>> (gdb) info reg >>> [...] >>> fs 0xffff 65535 >>> gs 0x33 51 >>> >>> Another one *after* the patch: >>> (gdb) info reg >>> [...] >>> fs 0xd8 216 >>> >>> >> This doesn't look right. This is the kernel's %fs, not usermode's >> (which should be 0). >> >> >>> gs 0x33 51 >>> (gdb) set $fs=0xffff >>> (gdb) info reg >>> [...] >>> fs 0xffff 65535 >>> gs 0x33 51 >>> (gdb) set $gs=0xffff >>> (gdb) info reg >>> [...] >>> fs 0xffff 65535 >>> gs 0xffff 65535 >>> >>> >> Hm. This shouldn't be possible since this is a bad selector, but I >> guess ptrace/gdb doesn't really know that. If you run the target (even >> single step it), these should revert to 0. >> >> > Here's a third session that looks better: > > (gdb) info reg > [...] > fs 0x0 0 > gs 0x33 51 > (gdb) set $fs=0xffff > (gdb) info reg > [...] > fs 0xffff 65535 > gs 0x33 51 > (gdb) set $gs=0xffff > (gdb) info reg > [...] > fs 0xffff 65535 > gs 0xffff 65535 > (gdb) n > Single stepping until exit from function main, > which has no line number information. > Cannot find user-level thread for LWP 10751: generic error > (gdb) set $gs=0x33 > (gdb) set $fs=0 > (gdb) n > Single stepping until exit from function main, > which has no line number information. > 0x08048c05 in __i686.get_pc_thunk.bx () > (gdb) info reg > [...] > fs 0x0 0 > gs 0x33 51 > > This is a -mm1 kernel + your efl_offset fix + the attached patch. > So the problem came from putreg still saving %gs to the stack where > there's no slot for it, whereas getreg got things right. > > Regards, > Frederik > > Signed-off-by: Frederik Deweerdt <[EMAIL PROTECTED]> > > > diff --git a/arch/i386/kernel/ptrace.c b/arch/i386/kernel/ptrace.c > index a803a49..d8f44db 100644 > --- a/arch/i386/kernel/ptrace.c > +++ b/arch/i386/kernel/ptrace.c > @@ -89,14 +89,14 @@ static int putreg(struct task_struct *child, > unsigned long regno, unsigned long value) > { > switch (regno >> 2) { > - case FS: > + case GS: > if (value && (value & 3) != 3) > return -EIO; > - child->thread.fs = value; > + child->thread.gs = value; > return 0; > case DS: > case ES: > - case GS: > + case FS: > if (value && (value & 3) != 3) > return -EIO; > value &= 0xffff; >
This patch is good. convert-i386-pda-code-to-use-%fs-fixes.patch touched this same code, but it didn't actually fix the problem. J - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/