lkml.org 
[lkml]   [2006]   [Dec]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [-mm patch] ptrace: make {put,get}reg work again for gs and fs
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.

> Andrew, this goes on top of ptrace-fix-efl_offset-value-according-to-i386-pda-changes.patch
> sent by Jeremy yesterday.
>

Don't think this is quite right yet. Assuming the %gs->%fs patch has
been applied, then the target %fs should be on its stack, and target %gs
will be in thread.gs. I'm not sure that thread.fs has any use, but I'd
want to double check vm86 to be sure.

J
-
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/

\
 
 \ /
  Last update: 2006-12-21 20:25    [W:1.569 / U:0.392 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site