Re: [PATCH v2 2/5] powerpc: kprobes: fix handling of function offsets on ABIv2

Masami Hiramatsu
2017-04-13T04:28:16Z

On Wed, 12 Apr 2017 16:28:25 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

> commit 239aeba76409 ("perf powerpc: Fix kprobe and kretprobe handling
> with kallsyms on ppc64le") changed how we use the offset field in struct
> kprobe on ABIv2. perf now offsets from the GEP (Global entry point) if an
> offset is specified and otherwise chooses the LEP (Local entry point).
>
> Fix the same in kernel for kprobe API users. We do this by extending
> kprobe_lookup_name() to accept an additional parameter to indicate the
> offset specified with the kprobe registration. If offset is 0, we return
> the local function entry and return the global entry point otherwise.
>
> With:
> # cd /sys/kernel/debug/tracing/
> # echo "p _do_fork" >> kprobe_events
> # echo "p _do_fork+0x10" >> kprobe_events
>
> before this patch:
> # cat ../kprobes/list
> c0000000000d0748 k _do_fork+0x8 [DISABLED]
> c0000000000d0758 k _do_fork+0x18 [DISABLED]
> c0000000000412b0 k kretprobe_trampoline+0x0 [OPTIMIZED]
>
> and after:
> # cat ../kprobes/list
> c0000000000d04c8 k _do_fork+0x8 [DISABLED]
> c0000000000d04d0 k _do_fork+0x10 [DISABLED]
> c0000000000412b0 k kretprobe_trampoline+0x0 [OPTIMIZED]
>
> Acked-by: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
> arch/powerpc/kernel/kprobes.c | 4 ++--
> arch/powerpc/kernel/optprobes.c | 4 ++--
> include/linux/kprobes.h | 2 +-
> kernel/kprobes.c | 7 ++++---
> 4 files changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> index a7aa7394954d..0732a0291ace 100644
> --- a/arch/powerpc/kernel/kprobes.c
> +++ b/arch/powerpc/kernel/kprobes.c
> @@ -42,14 +42,14 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
>
> struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
>
> -kprobe_opcode_t *kprobe_lookup_name(const char *name)
> +kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)

Hmm, if we do this change, it is natural that kprobe_lookup_name()
returns the address + offset.

Thank you,

--
Masami Hiramatsu <mhiramat@kernel.org>