From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] ARM: perf: allow tracing with kernel tracepoints events
Date: Thu, 26 Jun 2014 10:00:45 +0100 [thread overview]
Message-ID: <20140626090045.GB376@arm.com> (raw)
In-Reply-To: <CAFrcx1=gwRzU9heY8o9sphWUiga63NGdpN+cUh81Njr-X-OEGQ@mail.gmail.com>
On Wed, Jun 25, 2014 at 03:54:14PM +0100, Jean Pihet wrote:
> Hi Will,
Hello,
> On 25 June 2014 11:01, Will Deacon <will.deacon@arm•com> wrote:
> > On Fri, Jun 20, 2014 at 09:10:35AM +0100, Jean Pihet wrote:
> >> On 18 June 2014 14:53, Will Deacon <will.deacon@arm•com> wrote:
> >> > On Tue, Jun 17, 2014 at 06:11:05PM +0100, Jean Pihet wrote:
> >> >> Tested with perf record and tracepoints filtering (-e <tracepoint>), with
> >> >> unwinding using fp (--call-graph fp) and dwarf info (--call-graph dwarf).
> >> >
> >> > Whilst the old ACPS unwinding only needs PC, FP and SP, is this definitely
> >> > true for exidx and DWARF-based unwinding? Given that libunwind ends up
> >> > running a state machine for the latter, can we guarantee that we won't hit
> >> > instructions that require access to other general purpose registers?
> >> Yes. dwarf unwinding does not need anything extra. Once seeded all the
> >> rest is extracted from the dwarf trace info.
> >
> > Ok, but what if the LR isn't saved on the stack, for example? What if the
> > code you're trying to unwind is hand-written assembly annotated with CFI
> > directives?
> Then in that case the unwinding is not possible unless the
> hand-crafted asm is compatible with the requested unwinding method
> (fp, dwarf etc.). Do you expect problems there, if so can you give
> more details?
To use a readily available AArch64 example, take a look at
__kernel_gettimeofday in arch/arm64/kernel/vdso/gettimeofday.S
It starts by moving the link register into x2, so that it can later call
__do_get_tspec without clobbering it. Furthermore, it doesn't make use of
the stack at all.
How can you unwind that using your current code?
Will
next prev parent reply other threads:[~2014-06-26 9:00 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-16 15:01 [PATCH] [RFC] ARM: perf: allow tracing with kernel tracepoints events Jean Pihet
2014-05-19 15:39 ` Will Deacon
2014-05-19 15:58 ` Jean Pihet
2014-06-17 17:11 ` [PATCH] " Jean Pihet
2014-06-18 12:53 ` Will Deacon
2014-06-20 8:10 ` Jean Pihet
2014-06-25 9:01 ` Will Deacon
2014-06-25 14:54 ` Jean Pihet
2014-06-26 9:00 ` Will Deacon [this message]
2014-06-27 14:53 ` Jean Pihet
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