From mboxrd@z Thu Jan 1 00:00:00 1970 From: Masami Hiramatsu Date: Thu, 17 Jun 2021 15:02:39 +0000 Subject: Re: [PATCH -tip v7 09/13] kprobes: Setup instruction pointer in __kretprobe_trampoline_handler Message-Id: <20210618000239.f95de17418beae6d84ce783d@kernel.org> List-Id: References: <162209754288.436794.3904335049560916855.stgit@devnote2> <162209762943.436794.874947392889792501.stgit@devnote2> <20210617043909.fgu2lhnkxflmy5mk@treble> <20210617044032.txng4enhiduacvt6@treble> <20210617234001.54cd2ff60410ff82a39a2020@kernel.org> In-Reply-To: <20210617234001.54cd2ff60410ff82a39a2020@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Masami Hiramatsu , Andrii Nakryiko Cc: Josh Poimboeuf , Steven Rostedt , Ingo Molnar , X86 ML , Daniel Xu , linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kuba@kernel.org, mingo@redhat.com, ast@kernel.org, tglx@linutronix.de, kernel-team@fb.com, yhs@fb.com, linux-ia64@vger.kernel.org, Abhishek Sagar On Thu, 17 Jun 2021 23:40:01 +0900 Masami Hiramatsu wrote: > On Wed, 16 Jun 2021 23:40:32 -0500 > Josh Poimboeuf wrote: > > > On Wed, Jun 16, 2021 at 11:39:11PM -0500, Josh Poimboeuf wrote: > > > On Thu, May 27, 2021 at 03:40:29PM +0900, Masami Hiramatsu wrote: > > > > To simplify the stacktrace with pt_regs from kretprobe handler, > > > > set the correct return address to the instruction pointer in > > > > the pt_regs before calling kretprobe handlers. > > > > > > > > Suggested-by: Josh Poimboeuf > > > > Signed-off-by: Masami Hiramatsu > > > > Tested-by: Andrii Nakryik > > > > --- > > > > Changes in v3: > > > > - Cast the correct_ret_addr to unsigned long. > > > > --- > > > > kernel/kprobes.c | 3 +++ > > > > 1 file changed, 3 insertions(+) > > > > > > > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > > > > index 54e5b89aad67..1598aca375c9 100644 > > > > --- a/kernel/kprobes.c > > > > +++ b/kernel/kprobes.c > > > > @@ -1914,6 +1914,9 @@ unsigned long __kretprobe_trampoline_handler(struct pt_regs *regs, > > > > BUG_ON(1); > > > > } > > > > > > > > + /* Set the instruction pointer to the correct address */ > > > > + instruction_pointer_set(regs, (unsigned long)correct_ret_addr); > > > > + > > > > /* Run them. */ > > > > first = current->kretprobe_instances.first; > > > > while (first) { > > > > > > > > > > Hi Masami, > > > > > > I know I suggested this patch, but I believe it would only be useful in > > > combination with the use of UNWIND_HINT_REGS in SAVE_REGS_STRING. But I > > > think that would be tricky to pull off correctly. Instead, we have > > > UNWIND_HINT_FUNC, which is working fine. > > > > > > So I'd suggest dropping this patch, as the unwinder isn't actually > > > reading regs->ip after all. > > > > ... and I guess this means patches 6-8 are no longer necessary. > > OK, I also confirmed that dropping those patche does not make any change > on the stacktrace. > Let me update the series without those. Oops, Andrii, can you also test the kernel without this patch? (you don't need to drop patch 6-8) This changes the kretprobe to pass the return address via regs->ip to handler. Dynamic-event doesn't use it, but I'm not sure bcc is using it or not. Thank you, > > Thank you, > > > > > -- > > Josh > > > > > -- > Masami Hiramatsu -- Masami Hiramatsu