Re: [v5][PATCH] livepatch/ppc: Enable livepatching on powerpc
From: Torsten Duwe
Date: Tue Mar 08 2016 - 05:46:01 EST
On Tue, Mar 08, 2016 at 06:33:57PM +1100, Balbir Singh wrote:
> Changelog v5:
> 1. Removed the mini-stack frame created for klp_return_helper.
> As a result of the mini-stack frame, function with > 8
> arguments could not be patched
Did you get my previous mails? Those functions only require special
care, the _can_ be patched. In general, writing replacement functions
always requires attention!
Have you *tested* this patch? Replacing a function in the kernel?
Replacing a function in a module? For local calls? For global calls?
I strongly doubt so because it does not work this way.
To be fair, my last mail still was not 100% correct, but the conclusion
that the mini frame is not needed at all is invalid. Please leave it as it
was, I'm working on a test / demonstrator for how to handle these.
> + * Why do we need this?
> + * After patching we need to return to a trampoline return function
> + * that guarantees that we restore the TOC and return to the correct
> + * caller back
> + */
> + std r2, 24(r1) /* save TOC now, unconditionally. */
> + subf r0, r2, r0 /* Calculate offset from current TOC */
> + stw r0, 12(r1) /* Of the final LR and save it in CR+4 */
> + bl 5f
> +5: mflr r12
> + addi r12, r12, (klp_return_helper + 4 - .)@l
> + std r12, LRSAVE(r1)
> + * maybe inserting a klp_return_helper frame or not.
> + ld r2, 24(r1) /* restore TOC (saved by ftrace_caller) */
> + lwa r0, 12(r1) /* Load from CR+4, offset of LR w.r.t TOC */
> + add r0, r0, r2 /* Add the offset to current TOC */
> + std r0, LRSAVE(r1) /* save the real return address */
> + mtlr r0
> + blr
NAKed-by: Torsten Duwe <duwe@xxxxxxx>