Messages in this thread | | | Date | Fri, 24 May 2019 10:53:19 +0200 | From | Peter Zijlstra <> | Subject | Re: Getting empty callchain from perf_callchain_kernel() |
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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 )
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