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

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Message-ID: <4D9F7736.4070509@gmail.com>
Date:	Fri, 08 Apr 2011 14:59:34 -0600
From:	David Ahern <dsahern@...il.com>
To:	Stefan Hajnoczi <stefanha@...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 04/08/11 14:50, Stefan Hajnoczi wrote:
> 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.

Hmm.. ok. I thought it had been added - to trace-cmd at least. And I
recall Avi recently sending a patch to trace-cmd folks - I took that to
mean it works. Evidently, not.

David


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