Re: [Qemu-devel] Tracing guest virtual addresses

["Lluís Vilanova" <vilanova@ac.upc.edu>]

Lluís Vilanova writes:

> Jayanto Minocha writes:
>> Lluis,
>> My modifications were almost the same as those done by Emilio. There were
>> no memory trace events in the trace file.

> I'll take a look at it after I finish revamping the generic translation loop
> series (hopefully today).

I just sent a patch that should fix it:

  https://lists.gnu.org/archive/html/qemu-devel/2017-06/msg05491.html


Cheers,
  Lluis



>> -J

>> On Tue, Jun 20, 2017 at 10:20 AM, Emilio G. Cota <cota@braap.org> wrote:

>>> On Tue, Jun 20, 2017 at 14:02:02 +0300, Lluís Vilanova wrote:
>>> > Jayanto Minocha writes:
>>> >
>>> > > Hi,
>>> > > I think there have been a few threads on the mailing list regarding
>>> tracing
>>> > > guest virtual addresses for load and store instructions, but I have
>>> been
>>> > > unable to get it to work. I am trying this for an AArch64 machine, and
>>> am
>>> > > using the softmmu.
>>> >
>>> > > The tracing infrastructure provides the following event:
>>> >
>>> > > vcpu tcg guest_mem_before(...).
>>> >
>>> > > But that is only used to instrument the cpu_ld/cpu_st macros, which is
>>> only
>>> > > called in the case of a tlb miss.
>>> >
>>> > > I've been going over the archives, and it looks like I need to
>>> instrument
>>> > > tcg_out_tlb_load. Am I on the right path ?
>>> >
>>> > That event should trace all guest memory accesses performed by the CPU.
>>> If you
>>> > found any case where this does not hold, it is likely a bug and I'd
>>> appreciate
>>> > it if you can point me to the smallest possible failing example.
>>> 
>>> I'm having trouble with this as well, although I'm pretty sure I must be
>>> doing
>>> something wrong (never used the tracing infrastructure before). Here's what
>>> I'm doing:
>>> 
>>> $ git show --pretty=short
>>> commit e85c0d14014514a2f0faeae5b4c23fab5b234de4
>>> Merge: 65a0e3e 7f3cf2d
>>> Author: Peter Maydell <peter.maydell@linaro.org>
>>> 
>>> Merge remote-tracking branch 'remotes/mst/tags/for_upstream' into
>>> staging
>>> 
>>> 
>>> $ git diff
>>> diff --git a/accel/tcg/trace-events b/accel/tcg/trace-events
>>> index 2de8359..385a462 100644
>>> --- a/accel/tcg/trace-events
>>> +++ b/accel/tcg/trace-events
>>> @@ -2,7 +2,7 @@
>>> 
>>> # TCG related tracing (mostly disabled by default)
>>> # cpu-exec.c
>>> -disable exec_tb(void *tb, uintptr_t pc) "tb:%p pc=0x%"PRIxPTR
>>> +exec_tb(void *tb, uintptr_t pc) "tb:%p pc=0x%"PRIxPTR
>>> disable exec_tb_nocache(void *tb, uintptr_t pc) "tb:%p pc=0x%"PRIxPTR
>>> disable exec_tb_exit(void *last_tb, unsigned int flags) "tb:%p flags=%x"
>>> 
>>> diff --git a/trace-events b/trace-events
>>> index bae63fd..7df49a3 100644
>>> --- a/trace-events
>>> +++ b/trace-events
>>> @@ -106,7 +106,7 @@ vcpu guest_cpu_reset(void)
>>> #
>>> # Mode: user, softmmu
>>> # Targets: TCG(all)
>>> -disable vcpu tcg guest_mem_before(TCGv vaddr, uint8_t info) "info=%d",
>>> "vaddr=0x%016"PRIx64" info=%d"
>>> +vcpu tcg guest_mem_before(TCGv vaddr, uint8_t info) "info=%d",
>>> "vaddr=0x%016"PRIx64" info=%d"
>>> 
>>> # @num: System call number.
>>> # @arg*: System call argument value.
>>> 
>>> $ mkdir build
>>> $ cd build
>>> $ ../configure --target-list=arm-softmmu,x86_64-linux-user
>>> --enable-trace-backends=simple && make -j 12
>>> [...]
>>> 
>>> $ cat ../ev
>>> guest_mem_before_exec
>>> guest_mem_before_trans
>>> exec_tb
>>> 
>>> $ x86_64-linux-user/qemu-x86_64 -trace events=../ev /bin/date
>>> Tue Jun 20 13:11:49 EDT 2017
>>> 
>>> $ ls -lt | head | grep trace
>>> -rw-rw-r--  1 cota cota   169721 Jun 20 13:11 trace-2150
>>> 
>>> $ scripts/simpletrace.py trace-events-all trace-2150
>>> exec_tb 0.000 pid=2150 tb=0x7f5896667010 pc=0x4000801cc0
>>> exec_tb 21.648 pid=2150 tb=0x7f5896667088 pc=0x4000805c00
>>> [...]
>>> 
>>> 100% of the file is exec_tb lines, i.e. no memory references whatsoever.
>>> 
>>> Similar results with arm-softmmu.
>>> 
>>> Thanks,
>>> 
>>> Emilio
>>> 
>>>