On 11/18/2013 04:27 PM, Andi Kleen wrote:
>
> Proposed man page:
>
> NAME
> text_poke - Safely modify running instructions (x86)
>
> SYNOPSYS
> int text_poke(void *addr, const void *opcode, size_t len,
> void (*handler)(void), int timeout);
>
> DESCRIPTION
> The text_poke system allows to safely modify code that may
> be currently executing in parallel on other threads.
> Patch the instruction at addr with the new instructions
> at opcode of length len. The target instruction will temporarily
> be patched with a break point, before it is replaced
> with the final replacement instruction. When the break point
> hits the code handler will be called in the context
> of the thread. The handler does not save any registers
> and cannot return. Typically it would consist of the
> original instruction and then a jump to after the original
> instruction. The handler is only needed during the
> patching process and can be overwritten once the syscall
> returns. timeout defines an optional timout to indicate
> to the kernel how long the patching could be delayed.
> Right now it has to be 0.
>
I think I would prefer an interface which took a list of patch points,
or implemented only the aspects which are impossible to do in user space.
All we really need in the kernel is the IPI broadcasts - the rest can be
done in user space, including intercepting SIGTRAP. For userspace it is
probably the best to just put a thread to sleep until the patching is
done, which can be done with a futex.
One advantage with doing this in userspace is that the kernel doesn't
have to be responsible avoiding holding a thread due to a slightly
different SIGTRAP -- it will all come out after the signal handler is
restored, anyway.
That being said, the user space code would really need to be librarized.
-hpa
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
