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From: Mark Rutland <mark.rutland@arm.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Mark Brown <broonie@kernel.org>, Miroslav Benes <mbenes@suse.cz>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, live-patching@vger.kernel.org
Subject: Re: [RFC PATCH 0/3] arm64: Implement reliable stack trace
Date: Tue, 20 Oct 2020 11:03:52 +0100	[thread overview]
Message-ID: <20201020100352.GA48360@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20201016111431.GB84361@C02TD0UTHF1T.local>

On Fri, Oct 16, 2020 at 12:14:31PM +0100, Mark Rutland wrote:
> Mark B's reply dropped this, but the next paragraph covered that:
> 
> | I was planning to send a mail once I've finished writing a test, but
> | IIUC there are some windows where ftrace/kretprobes
> | detection/repainting may not work, e.g. if preempted after
> | ftrace_return_to_handler() decrements curr_ret_stack, but before the
> | arch trampoline asm restores the original return addr. So we might
> | need something like an in_return_trampoline() to detect and report
> | that reliably.
> 
> ... so e.g. for a callchain A->B->C, where C is instrumented there are
> windows where B might be missing from the trace, but the trace is
> reported as reliable.

I'd missed a couple of details, and I think I see how each existing
architecture prevents this case now.

Josh, just to confirm the x86 case, am I right in thinking that the ORC
unwinder will refuse to unwind from the return_to_handler and
kretprobe_trampoline asm? IIRC objtool shouldn't build unwind info for
those as return_to_handler is marked with SYM_CODE_{START,END}() and
kretprobe_trampoline is marked with STACK_FRAME_NON_STANDARD().

Both powerpc and s390 refuse to reliably unwind through exceptions, so
they can rely on function call boundaries to keep the callchain in a
sane state.

Thanks,
Mark.

  reply	other threads:[~2020-10-20 10:04 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20201012172605.10715-1-broonie@kernel.org>
     [not found] ` <alpine.LSU.2.21.2010151533490.14094@pobox.suse.cz>
     [not found]   ` <20201015141612.GC50416@C02TD0UTHF1T.local>
     [not found]     ` <20201015154951.GD4390@sirena.org.uk>
2020-10-15 21:29       ` [RFC PATCH 0/3] arm64: Implement reliable stack trace Josh Poimboeuf
2020-10-16 11:14         ` Mark Rutland
2020-10-20 10:03           ` Mark Rutland [this message]
2020-10-20 15:58             ` Josh Poimboeuf
2020-10-16 12:15         ` Mark Brown
2020-10-19 23:41           ` Josh Poimboeuf
2020-10-20 15:39             ` Mark Brown
2020-10-20 16:28               ` Josh Poimboeuf

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