"Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> writes:
> diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> index fa0921410fa4..e6837e85ec28 100644
> --- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> +++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> @@ -99,13 +99,37 @@ ftrace_call:
> bl ftrace_stub
> nop
>
> - /* Load ctr with the possibly modified NIP */
> - ld r3, _NIP(r1)
> - mtctr r3
> + /* Load the possibly modified NIP */
> + ld r15, _NIP(r1)
> +
> #ifdef CONFIG_LIVEPATCH
> - cmpd r14,r3 /* has NIP been altered? */
> + cmpd r14, r15 /* has NIP been altered? */
> +#endif
> +
> +#if defined(CONFIG_LIVEPATCH) && defined(CONFIG_KPROBES_ON_FTRACE)
> + beq 1f
> +
> + /* Check if there is an active kprobe on us */
> + subi r3, r14, 4
> + bl is_current_kprobe_addr
> + nop
> +
> + /*
> + * If r3 == 1, then this is a kprobe/jprobe.
> + * else, this is livepatched function.
> + *
> + * The subsequent conditional branch for livepatch_handler
> + * will use the result of this compare. For kprobe/jprobe,
> + * we just need to branch to the new NIP, so nothing special
> + * is needed.
> + */
> + cmpdi r3, 1
> +1:
> #endif
I added some more comments. Hopefully I got them right :D
#if defined(CONFIG_LIVEPATCH) && defined(CONFIG_KPROBES_ON_FTRACE)
+ /* NIP has not been altered, skip over further checks */
beq 1f
/* Check if there is an active kprobe on us */
@@ -118,10 +119,11 @@ ftrace_call:
* If r3 == 1, then this is a kprobe/jprobe.
* else, this is livepatched function.
*
- * The subsequent conditional branch for livepatch_handler
- * will use the result of this compare. For kprobe/jprobe,
- * we just need to branch to the new NIP, so nothing special
- * is needed.
+ * The conditional branch for livepatch_handler below will use the
+ * result of this comparison. For kprobe/jprobe, we just need to branch
to
+ * the new NIP, not call livepatch_handler. The branch below is bne, so
we
+ * want CR0[EQ] to be true if this is a kprobe/jprobe. Which means we
want
+ * CR0[EQ] = (r3 == 1).
*/
cmpdi r3, 1
1:
@@ -147,7 +149,10 @@ ftrace_call:
addi r1, r1, SWITCH_FRAME_SIZE
#ifdef CONFIG_LIVEPATCH
- /* Based on the cmpd above, if the NIP was altered handle livepatch */
+ /*
+ * Based on the cmpd or cmpdi above, if the NIP was altered and we're
+ * not on a kprobe/jprobe, then handle livepatch.
+ */
bne- livepatch_handler
#endif
cheers
