linux-kernel - Re: trace-cmd errors on kvm events

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Date:	Fri, 8 Apr 2011 21:50:49 +0100
From:	Stefan Hajnoczi <stefanha@...il.com>
To:	David Ahern <dsahern@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	KVM mailing list <kvm@...r.kernel.org>
Subject: Re: trace-cmd errors on kvm events

On Fri, Apr 8, 2011 at 7:53 PM, David Ahern <dsahern@...il.com> wrote:
> 2.6.38.2 kernel with trace-cmd git pulled this morning:
>
> trace-cmd record -e kvm
>
> trace-cmd report 2>&1 | less
>
> trace-cmd: No such file or directory
>  function ftrace_print_symbols_seq not defined
>  failed to read event print fmt for kvm_nested_vmexit_inject
>  function ftrace_print_symbols_seq not defined
>  failed to read event print fmt for kvm_nested_vmexit
>  function ftrace_print_symbols_seq not defined
>  failed to read event print fmt for kvm_exit
>  bad op token {
>  failed to read event print fmt for kvm_emulate_insn
>
>        qemu-kvm-1864  [002]  2253.714134: kvm_entry:            vcpu 1
>        qemu-kvm-1863  [008]  2253.714136: kvm_exit:             [FAILED
> TO PARSE] exit_reason=44 guest_rip=0xc01185ed isa=1 info1=4272 info2=0
>        qemu-kvm-1864  [002]  2253.714138: kvm_exit:             [FAILED
> TO PARSE] exit_reason=44 guest_rip=0xc01185ed isa=1 info1=4272 info2=0
>        qemu-kvm-1863  [008]  2253.714145: kvm_emulate_insn:     [FAILED
> TO PARSE] rip=3222373869 csbase=0 len=2 insn=<89>^H]<C3><8B>^U<EC><95>K<C0>U
> <89><E5>]<8D>^E flags=5 failed=0
>
> I have not used trace-cmd much, so I am not familiar with the code. Is
> this a known issue? Suggestions on how to debug?

I think there have been issues for a long time.  I've never gotten
perf or trace-cmd to be happy with kvm:* events.  Here is a related
thread from a while back:

https://lkml.org/lkml/2010/5/26/194

When I looked a while back the problem was due to how there is some
preprocessor magic in Linux that ends up exporting C expressions as
strings to userspace and neither perf nor trace-cmd have the parsing
smarts to evaluate the C expressions at runtime.

I ended up using ftrace instead which handles everything inside the
kernel and compiles in those C expressions.

Stefan
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