From: Masami Hiramatsu <mhiramat@kernel.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Josh Poimboeuf <jpoimboe@redhat.com>, X86 ML <x86@kernel.org>,
Daniel Xu <dxu@dxuuu.xyz>,
linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
kuba@kernel.org, mingo@redhat.com, ast@kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
Peter Zijlstra <peterz@infradead.org>,
kernel-team@fb.com, yhs@fb.com, linux-ia64@vger.kernel.org,
Abhishek Sagar <sagar.abhishek@gmail.com>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>
Subject: Re: [PATCH -tip v8 05/13] x86/kprobes: Add UNWIND_HINT_FUNC on kretprobe_trampoline code
Date: Sat, 10 Jul 2021 00:31:40 +0900 [thread overview]
Message-ID: <20210710003140.8e561ad33d42f9ac78de6a15@kernel.org> (raw)
In-Reply-To: <YOK8pzp8B2V+1EaU@gmail.com>
On Mon, 5 Jul 2021 10:02:47 +0200
Ingo Molnar <mingo@kernel.org> wrote:
>
> * Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> > From: Josh Poimboeuf <jpoimboe@redhat.com>
> >
> > Add UNWIND_HINT_FUNC on kretporbe_trampoline code so that ORC
> > information is generated on the kretprobe_trampoline correctly.
>
> What is a 'kretporbe'?
Oops, it's a typo.
>
> > Note that when the CONFIG_FRAME_POINTER=y, since the
> > kretprobe_trampoline skips updating frame pointer, the stack frame
> > of the kretprobe_trampoline seems non-standard. So this marks it
> > is STACK_FRAME_NON_STANDARD() and undefine UNWIND_HINT_FUNC.
>
> What does 'marks it is' mean?
Sorry, I meant, this marks the kretprobe_trampoline as non-standard
stack frame by STACK_FRAME_NON_STANDARD().
>
> 'undefine' UNWIND_HINT_FUNC?
>
> Doesn't the patch do the exact opposite:
>
> > +#define UNWIND_HINT_FUNC \
> > + UNWIND_HINT(ORC_REG_SP, 8, UNWIND_HINT_TYPE_FUNC, 0)
>
> But it does undefine it in a specific spot:
Yes, if you think this is not correct way, what about the following?
#ifdef CONFIG_FRAME_POINTER
STACK_FRAME_NON_STANDARD(kretprobe_trampoline);
#define KRETPROBE_UNWIND_HINT_FUNC
#else
#define KRETPROBE_UNWIND_HINT_FUNC UNWIND_HINT_FUNC
#endif
> > Anyway, with the frame pointer, FP unwinder can unwind the stack
> > frame correctly without that hint.
> >
> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> > Tested-by: Andrii Nakryik <andrii@kernel.org>
>
> I have to say these changelogs are very careless.
Sorry for inconvenience...
>
> > +#else
> > +
>
> In headers, in longer CPP blocks, please always mark the '#else' branch
> with what it is the else branch of.
OK.
>
> See the output of:
>
> kepler:~/tip> git grep '#else' arch/x86/include/asm/ | head
Thanks for the hint!
>
> > +#ifdef CONFIG_FRAME_POINTER
> > +/*
> > + * kretprobe_trampoline skips updating frame pointer. The frame pointer
> > + * saved in trampoline_handler points to the real caller function's
> > + * frame pointer. Thus the kretprobe_trampoline doesn't seems to have a
> > + * standard stack frame with CONFIG_FRAME_POINTER=y.
> > + * Let's mark it non-standard function. Anyway, FP unwinder can correctly
> > + * unwind without the hint.
>
> s/doesn't seems to have a standard stack frame
> /doesn't have a standard stack frame
>
> There's nothing 'seems' about the situation - it's a non-standard function
> entry and stack frame situation, and the unwinder needs to know about it.
OK.
>
> > +STACK_FRAME_NON_STANDARD(kretprobe_trampoline);
> > +#undef UNWIND_HINT_FUNC
> > +#define UNWIND_HINT_FUNC
> > +#endif
> > /*
> > * When a retprobed function returns, this code saves registers and
> > * calls trampoline_handler() runs, which calls the kretprobe's handler.
> > @@ -1031,6 +1044,7 @@ asm(
> > /* We don't bother saving the ss register */
> > #ifdef CONFIG_X86_64
> > " pushq %rsp\n"
> > + UNWIND_HINT_FUNC
> > " pushfq\n"
> > SAVE_REGS_STRING
> > " movq %rsp, %rdi\n"
> > @@ -1041,6 +1055,7 @@ asm(
> > " popfq\n"
> > #else
> > " pushl %esp\n"
> > + UNWIND_HINT_FUNC
> > " pushfl\n"
> > SAVE_REGS_STRING
> > " movl %esp, %eax\n"
>
> Why not provide an appropriate annotation method in <asm/unwind_hints.h>,
> so that other future code can use it too instead of reinventing the wheel?
Would you mean we should define the UNWIND_HINT_FUNC as a macro
which depends on CONFIG_FRAME_POINTER, in <asm/unwind_hints.h>?
Josh, what would you think?
Thank you,
--
Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2021-07-09 15:31 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-18 7:05 [PATCH -tip v8 00/13] kprobes: Fix stacktrace with kretprobes on x86 Masami Hiramatsu
2021-06-18 7:05 ` [PATCH -tip v8 01/13] ia64: kprobes: Fix to pass correct trampoline address to the handler Masami Hiramatsu
2021-07-05 7:46 ` Ingo Molnar
2021-07-05 10:05 ` Masami Hiramatsu
2021-06-18 7:05 ` [PATCH -tip v8 02/13] kprobes: treewide: Replace arch_deref_entry_point() with dereference_symbol_descriptor() Masami Hiramatsu
2021-07-05 7:48 ` Ingo Molnar
2021-07-05 12:03 ` Masami Hiramatsu
2021-07-07 18:28 ` Andrii Nakryiko
2021-07-08 4:08 ` Masami Hiramatsu
2021-06-18 7:05 ` [PATCH -tip v8 03/13] kprobes: treewide: Remove trampoline_address from kretprobe_trampoline_handler() Masami Hiramatsu
2021-07-05 7:03 ` Ingo Molnar
2021-07-05 10:03 ` Masami Hiramatsu
2021-07-05 7:49 ` Ingo Molnar
2021-06-18 7:05 ` [PATCH -tip v8 04/13] kprobes: Add kretprobe_find_ret_addr() for searching return address Masami Hiramatsu
2021-07-05 7:42 ` Ingo Molnar
2021-07-05 14:11 ` Masami Hiramatsu
2021-06-18 7:06 ` [PATCH -tip v8 05/13] x86/kprobes: Add UNWIND_HINT_FUNC on kretprobe_trampoline code Masami Hiramatsu
2021-07-05 8:02 ` Ingo Molnar
2021-07-09 15:31 ` Masami Hiramatsu [this message]
2021-07-10 1:41 ` Masami Hiramatsu
2021-07-10 19:01 ` Josh Poimboeuf
2021-07-10 19:24 ` [PATCH 1/2] objtool: Add frame-pointer-specific function ignore Josh Poimboeuf
2021-07-11 1:16 ` Masami Hiramatsu
2021-07-29 2:31 ` Masami Hiramatsu
2021-07-10 19:25 ` [PATCH 2/2] objtool: Ignore unwind hints for ignored functions Josh Poimboeuf
2021-07-11 2:07 ` Masami Hiramatsu
2021-06-18 7:06 ` [PATCH -tip v8 06/13] ARC: Add instruction_pointer_set() API Masami Hiramatsu
2021-06-18 7:06 ` [PATCH -tip v8 07/13] ia64: " Masami Hiramatsu
2021-06-18 7:06 ` [PATCH -tip v8 08/13] arm: kprobes: Make a space for regs->ARM_pc at kretprobe_trampoline Masami Hiramatsu
2021-07-05 8:04 ` Ingo Molnar
2021-07-05 14:40 ` Masami Hiramatsu
2021-06-18 7:06 ` [PATCH -tip v8 09/13] kprobes: Enable stacktrace from pt_regs in kretprobe handler Masami Hiramatsu
2021-06-18 14:04 ` Josh Poimboeuf
2021-06-18 7:06 ` [PATCH -tip v8 10/13] x86/kprobes: Push a fake return address at kretprobe_trampoline Masami Hiramatsu
2021-07-05 8:17 ` Ingo Molnar
2021-07-09 14:55 ` Masami Hiramatsu
2021-06-18 7:07 ` [PATCH -tip v8 11/13] x86/unwind: Recover kretprobe trampoline entry Masami Hiramatsu
2021-07-05 11:36 ` Peter Zijlstra
2021-07-05 15:42 ` Masami Hiramatsu
2021-07-06 7:55 ` Peter Zijlstra
2021-07-06 15:11 ` Steven Rostedt
2021-07-07 8:20 ` Peter Zijlstra
2021-07-07 8:36 ` Peter Zijlstra
2021-07-07 10:15 ` Masami Hiramatsu
2021-07-07 10:20 ` Peter Zijlstra
2021-07-07 10:45 ` Masami Hiramatsu
2021-07-07 13:29 ` Masami Hiramatsu
2021-07-07 14:42 ` Matt Wu
2021-07-11 14:09 ` Masami Hiramatsu
2021-07-11 15:28 ` Matt Wu
2021-07-12 4:57 ` Masami Hiramatsu
2021-06-18 7:07 ` [PATCH -tip v8 12/13] tracing: Show kretprobe unknown indicator only for kretprobe_trampoline Masami Hiramatsu
2021-06-18 7:07 ` [PATCH -tip v8 13/13] x86/kprobes: Fixup return address in generic trampoline handler Masami Hiramatsu
2021-07-05 8:34 ` Ingo Molnar
2021-07-06 12:57 ` Masami Hiramatsu
2021-06-18 17:44 ` [PATCH -tip v8 00/13] kprobes: Fix stacktrace with kretprobes on x86 Andrii Nakryiko
2021-06-28 13:50 ` Masami Hiramatsu
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