Re: [Qemu-devel] Tracing guest virtual addresses

[Jayanto Minocha]

Lluis,

My modifications were almost the same as those done by Emilio. There were
no memory trace events in the trace file.

-J

On Tue, Jun 20, 2017 at 10:20 AM, Emilio G. Cota <address@hidden> 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 <address@hidden>
>
>     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
>
>