Em Mon, Jan 26, 2015 at 01:51:23PM +0000, Russell King - ARM Linux escreveu:
> On Mon, Jan 26, 2015 at 10:27:11AM +0000, Will Deacon wrote:
> > On Sun, Jan 25, 2015 at 03:56:52PM +0000, Russell King - ARM Linux wrote:
> > > On Sat, Jan 24, 2015 at 04:23:42PM -0600, Felipe Balbi wrote:
> > > > yeah, I'll try a few older kernels, also see if I can reproduce on other
> > > > boards.
> > > Perf works for me with CONFIG_FRAME_POINTER=y, but that's only for kernel
> > > space, and for userspace where the programs have been built for ARM mode
> > > with frame pointers.
> > > The kernel may work without CONFIG_FRAME_POINTER set, but I've never
> > > tested that, and I'd suggest that (given my experience looking at oops
> > > dumps) it's not all that reliable.
> > > Lastly, userspace without frame pointers is pretty much hopeless.
> > FWIW, perf can now use libunwind for unwinding the userspace side of
> > things, so it's not quite as bad as it used to be. For the kernel side,
> > if the unwinder isn't working properly it would be nice to know *why*,
> > but I agree that it tends to be far flakier than the frame-pointer method.
> I don't see how userspace could be unwound without capturing the entire
> userspace stack on every perf event - and that could be a considerable
> size. We have no way to know within the kernel which words on the
That is what you can do using 'perf record --call-graph dwarf':
-g enables call-graph recording
--call-graph <mode[,dump_size]>
setup and enables call-graph (stack chain/backtrace)
recording: fp dwarf
That will use:
PERF_SAMPLE_REGS_USER = 1U << 12,
PERF_SAMPLE_STACK_USER = 1U << 13,
struct perf_event_attr {
<SNIP>
/*
* Defines set of user regs to dump on samples.
* See asm/perf_regs.h for details.
*/
__u64 sample_regs_user;
/*
* Defines size of the user stack to dump on samples.
*/
__u32 sample_stack_user;
<SNIP>
}
> userspace stack are part of the callchain and which aren't - the only
> way we'd know is by loading the userspace's unwind tables, having the
> kernel parsing them and generate a list of functions.
Or deferring it to userspace to do that later.
- Arnaldo
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