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From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kairui Song <kasong@redhat.com>, Alexei Starovoitov <ast@fb.com>,
	Song Liu <songliubraving@fb.com>,
	lkml <linux-kernel@vger.kernel.org>,
	Kernel Team <Kernel-team@fb.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	"bpf@vger.kernel.org" <bpf@vger.kernel.org>
Subject: Re: Getting empty callchain from perf_callchain_kernel()
Date: Fri, 24 May 2019 10:53:19 +0200	[thread overview]
Message-ID: <20190524085319.GE2589@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190523152413.m2pbnamihu3s2c5s@treble>

On Thu, May 23, 2019 at 10:24:13AM -0500, Josh Poimboeuf wrote:

> Here's the latest version which should fix it in all cases (based on
> tip/master):
> 
>   https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/commit/?h=bpf-orc-fix

That patch suffers an inconsitency, the comment states:

  'if they have "jump_table" in the name'

while the actual code implements:

  'if the name starts with "jump_table"'

Other than that, I suppose that works just fine ;-)

> There's no need to put special cases in the FP unwinder when we can
> instead just fix the frame pointer usage in the JIT code.
> 
> For ORC, I'm thinking we may be able to just require that all generated
> code (BPF and others) always use frame pointers.  Then when ORC doesn't
> recognize a code address, it could try using the frame pointer as a
> fallback.

Yes, this seems like a sensible approach. We'd also have to audit the
ftrace and kprobe trampolines, IIRC they only do framepointer setup for
CONFIG_FRAME_POINTER currently, which should be easy to fix (after the
patches I have to fix the FP generation in the first place:

  https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=x86/wip
)

  parent reply	other threads:[~2019-05-24  8:53 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-16 23:51 Song Liu
2019-05-17  7:46 ` Peter Zijlstra
2019-05-17  8:10   ` Peter Zijlstra
2019-05-17  8:15     ` Kairui Song
2019-05-17  8:32       ` Kairui Song
2019-05-17 16:22         ` Song Liu
2019-05-17  9:10       ` Peter Zijlstra
2019-05-17 18:40         ` Song Liu
2019-05-17 21:06           ` Alexei Starovoitov
2019-05-17 21:48             ` Song Liu
2019-05-19 18:07               ` Kairui Song
2019-05-20 17:22                 ` Song Liu
2019-05-22 13:51                   ` Peter Zijlstra
2019-05-19 18:06         ` Kairui Song
2019-05-20 17:16           ` Song Liu
2019-05-20 17:19           ` Song Liu
2019-05-22 14:02           ` Peter Zijlstra
2019-05-22 14:49             ` Alexei Starovoitov
2019-05-22 17:45               ` Josh Poimboeuf
2019-05-22 23:46                 ` Josh Poimboeuf
2019-05-23  6:48                   ` Kairui Song
2019-05-23  8:27                     ` Song Liu
2019-05-23  9:11                       ` Kairui Song
2019-05-23 13:32                     ` Josh Poimboeuf
2019-05-23 14:50                       ` Kairui Song
2019-05-23 15:24                         ` Josh Poimboeuf
2019-05-23 16:41                           ` Kairui Song
2019-05-23 17:27                             ` Josh Poimboeuf
2019-05-24  2:20                               ` Kairui Song
2019-05-24 23:23                                 ` Josh Poimboeuf
2019-05-27 11:57                                   ` Kairui Song
2019-06-06 16:04                                     ` Song Liu
2019-06-06 23:58                                       ` Josh Poimboeuf
2019-06-11 21:03                                       ` Josh Poimboeuf
2019-05-24  8:53                           ` Peter Zijlstra [this message]
2019-05-24 13:05                             ` Josh Poimboeuf
2019-06-12  3:05                             ` Josh Poimboeuf
2019-06-12  8:54                               ` Peter Zijlstra
2019-06-12 14:50                                 ` Josh Poimboeuf
2019-06-13 20:26                                   ` Josh Poimboeuf
2019-06-12 13:10                               ` Steven Rostedt
2019-06-12 14:26                                 ` Josh Poimboeuf
2019-05-22 18:07       ` Josh Poimboeuf
2019-05-22 21:55         ` Alexei Starovoitov
2019-05-17 16:32     ` Song Liu

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