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
/* 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;
--
vda
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