Re: [Qemu-devel] anybody using MMIO tracing?

[Hollis Blanchard <hollis_blanchard@mentor.com>]

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On 11/06/2015 03:15 AM, Peter Maydell wrote:
> On 6 November 2015 at 11:12, Stefan Hajnoczi <stefanha@gmail.com> wrote:
>> On Mon, Nov 02, 2015 at 09:18:03AM -0800, Hollis Blanchard wrote:
>>> I'm trying to use the memory_region_ops_read/write tracepoints. They produce
>>> output like this:
>>>
>>>     memory_region_ops_write 0.000 pid=8861 mr=0x185b1e8 addr=0x0
>>>     value=0x3 size=0x4
>>>     memory_region_ops_write 165.000 pid=8861 mr=0x185b1e8 addr=0x80
>>>     value=0xffffffff size=0x4
>>>     memory_region_ops_write 155.000 pid=8861 mr=0x1914240 addr=0x0
>>>     value=0x3 size=0x4
>>>     memory_region_ops_write 2.000 pid=8861 mr=0x185b320 addr=0x0
>>>     value=0x3 size=0x4
>>>     memory_region_ops_write 134.000 pid=8861 mr=0x1914240 addr=0x4
>>>     value=0x80 size=0x4
>>>
>>> How do I discover which devices are represented by MemoryRegions 0x185b1e8
>>> and 0x1914240? Or alternatively how do I discover the full addresses?
>> As a KVM user I use the kvm:kvm_mmio and kvm:kvm_pio kernel trace
>> events.
> Is there a reason why we can't print the mr->name in this tracing?

That works, and I was going to suggest it if there's no better answer. 
I'm not sure however if it's possible to disambiguate the trace messages 
if you have multiple instances of the same device type. Other 
improvements could be important too, like displaying which core was 
performing the access. So maybe just displaying the name first is a good 
step forward for now, and separately there's an improvement wishlist for 
the future.

I was just confused because Paolo's original patch 
<http://osdir.com/ml/qemu-devel/2013-07/msg04848.html> said "This is 
quite handy to debug softmmu targets", so I figured I must be missing 
something that would make it handy. :-)

By the way, docs/tracing.txt says:

    The "simple" backend currently does not capture string arguments, it
    simply
    records the char* pointer value instead of the string that is
    pointed to.

This seems no longer to be the case, because string arguments display 
fine for me...

Hollis Blanchard
Mentor Graphics Emulation Division


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