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

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Date:   Thu, 13 Apr 2017 13:28:04 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/5] powerpc: kprobes: fix handling of function
 offsets on ABIv2

On Wed, 12 Apr 2017 16:28:25 +0530
"Naveen N. Rao" <naveen.n.rao@...ux.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@...ux.vnet.ibm.com>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.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@...nel.org>