Re: [PATCH v10 3.3-rc2 1/9] uprobes: Install and removebreakpoints.

[Srikar Dronamraju]

* Denys Vlasenko <vda.linux@xxxxxxxxxxxxxx> [2012-02-08 10:40:30]:

> On Tue, Feb 7, 2012 at 6:17 PM, Srikar Dronamraju
> <srikar@xxxxxxxxxxxxxxxxxx> wrote:
> > Changelog: (Since v10): Add code to clear REX.B prefix pointed out by Denys Vlasenko
> > and fix suggested by Masami Hiramatsu.
> ...
> > +       /*
> > +        * Point cursor at the modrm byte.  The next 4 bytes are the
> > +        * displacement.  Beyond the displacement, for some instructions,
> > +        * is the immediate operand.
> > +        */
> > +       cursor = uprobe->insn + insn_offset_modrm(insn);
> > +       insn_get_length(insn);
> > +       if (insn->rex_prefix.nbytes)
> > +               *cursor &= 0xfe;        /* Clearing REX.B bit */
> 
> It looks like cursor points to mod/reg/rm byte, not rex byte.
> Comment above says it too. You seem to be clearing a bit
> in a wrong byte. I think it should be


Oh okay, Will correct this and send out a new patch.


> 
>         /* Clear REX.b bit (extension of MODRM.rm field):
>          * we want to encode rax/rcx, not r8/r9.
>          */
>         if (insn->rex_prefix.nbytes)
>                 insn->rex_prefix.bytes[0] &= 0xfe;

-- 
Thanks and Regards
Srikar

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