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Res: [Qemu-devel] full dynamic instruction trace for MIPS target


From: Boris Cámara
Subject: Res: [Qemu-devel] full dynamic instruction trace for MIPS target
Date: Tue, 6 Apr 2010 16:18:08 -0700 (PDT)

Hi Vince,
The aproach you are using on http://www.csl.cornell.edu/~vince/projects/qemu-trace/ to get the PC dump is similar to mine but as you dont disable the TB caches It is not a full execution trace. You only dump the PC when they are compiled and inserted on the TB cache. When qemu needs to execute the same code again, tb_find_slow() will find it was cached so your code wont dump the executed PCs again beacuse tb_gen_code()  wont be called this time.

On    http://www.csl.cornell.edu/~vince/projects/qemusim/ I found the same logic because you call the helper function inside of gen_intermediate_code_internal() which is called by tb_find_slow() too.

So, as far as i understand if tb_find_slow() find the  previously cached PC on the TB vector, your dump_pc() helper functions will not be called again for this TB.

Did you get correct values for your counters in bbvs[bb] ?

I didnt run your patch yet so I m not sure that I said is 100% correct. :)



De: Vince Weaver <address@hidden>
Para: Boris Cámara <address@hidden>
Cc: address@hidden
Enviadas: Segunda-feira, 5 de Abril de 2010 22:41:52
Assunto: Re: [Qemu-devel] full dynamic instruction trace for MIPS target


> I think the correct way to get the full instruction trace on a MIPS
> emulated processor is:

the way you describe is slow because you are constantly re-generating the
TBs.  The best way to do this is to add your instrumentation to the TBs.

I have code that does that for a recent version of Qemu here:
  http://www.csl.cornell.edu/~vince/projects/qemusim/

although it outputs Basic-Block vectors, not a full memory trace like you
want.  It has been validated to match proper instruction counts using
hardware performnce counters though.

I also have code creating full instruction/memory traces for Qemu MIPS
that can be found here:
  http://www.csl.cornell.edu/~vince/projects/qemu-trace/

but it's against Qemu from 2007 pre-dating the TCG changeover so of
limited use probably.  I hvae some code somewhere that updated this to
work with TCG but I don't know what happened to it.

Vince





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