Re: [PATCH v2 2.6.38-rc8-tip 6/20] 6: x86: analyze instruction and determine fixups.

Srikar Dronamraju
2011-03-18T18:56:19Z

* Roland McGrath <roland@hack.frob.com> [2011-03-18 11:36:29]:

> > handle_riprel_insn() returns 0 if the instruction is not rip-relative
> > returns 1 if its rip-relative but can use XOL slots.
> > returns -1 if its rip-relative but cannot use XOL.
> >
> > We dont see any instructions that are rip-relative and cannot use XOL.
> > so the check and return are redundant and I will remove that in the next
> > patch.
>
> How is that? You can only adjust a rip-relative instruction correctly if
> the instruction copy is within 2GB of the original target address, which
> cannot be presumed to always be the case in user address space layout
> (unlike the kernel).
>

So we rewrite the copy of instruction (stored in XOL) such that it
accesses its memory operand indirectly thro a scratch register.
The contents of the scratch register are stored before singlestep and
restored later.

Can you please tell us if this doesnt work?

--
Thanks and Regards
Srikar