Messages in this thread | | | Date | Thu, 1 Oct 2015 12:47:06 -0700 | From | Drew Richardson <> | Subject | Re: [PATCH] arm: perf: Fix userspace call stack walking |
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On Thu, Oct 01, 2015 at 08:10:41PM +0100, Russell King - ARM Linux wrote: > On Thu, Oct 01, 2015 at 10:26:47AM -0700, Drew Richardson wrote: > > The layout of stack frames has changed over time. Testing using a > > arm-linux-gnueabi gcc-4.2 from 2007 the original code didn't work but > > this new code does. It also works with clang as well as newer versions > > of gcc. > > Can you point to a modern ARM distribution where perf actually works with > calltraces into userspace?
I am not aware of an ARM distribution where it works, that's the problem. I optimistically said 'The layout of stack frames has changed over time,' but I couldn't find any case where it worked (including digging up an ARM compiler from 2007)
This is from 4.3-rc3 on Gentoo using 'perf record -ga ./dhrystone' then 'perf report -g'.
1.36% dhrystone dhrystone [.] Func_3 | --- Func_3 | |--85.61%-- 0x59 | --14.39%-- 0x7ec5d5ac
And this is after the proposed changes
1.99% dhrystone dhrystone [.] Func_3 | --- Func_3 | |--87.45%-- cmd_report | Proc_1 | main | 0x0 | --12.55%-- Proc_1 main 0x0
The call stack unwinding isn't perfect, for example leaf functions may not write a stack frame at all, but it's hopefully better than it was.
Drew Richardson
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