Re: [Qemu-devel] [PATCH, RFC] trace: implement guest tracepoint passthrough

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Aug 26, 2011 at 8:06 PM, Blue Swirl <blauwirbel@gmail.com> wrote:
> Let guests inject tracepoint data via fw_cfg device.
>
> Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
> ---
> The patch is used like this:
> ../configure --with-guest-trace-file=/src/openbios-devel/trace-events
> make
> sparc64-softmmu/qemu-system-sparc64 -trace file=foo
> # ugly hack to combine the file, but my laziness^Wpython-fu is too
> weak to add handling of "--guest-trace-file
> /src/openbios-devel/trace-events" to simpletrace.py
> cat ../trace-events /src/openbios-devel/trace-events >/tmp/trace-events
> # examine trace file with OpenBIOS trace data with simpletrace.py
> ../scripts/simpletrace.py /tmp/trace-events foo
> ob_ide_read_blocks 0.000 dest=0xfff0bed0 blk=0x0 n=0x1
> ob_ide_read_blocks 6491.806 dest=0xfff0bed0 blk=0x0 n=0x1
>
> An example of a generated guest-trace.c file:
> /* This file is autogenerated by tracetool, do not edit. */
> #include "trace.h"
> #include "guest-trace.h"
>
> void guest_trace(uint64_t event_id, uint64_t arg1, uint64_t arg2,
>                 uint64_t arg3, uint64_t arg4, uint64_t arg5, uint64_t arg6)
>
> {
>    switch (event_id) {
>
>    case 0:
>        trace_esp_do_command(arg1, arg2, arg3);
>        break;
>
>    case 1:
>        trace_ob_ide_pio_insw(arg1);
>        break;
>
>    case 2:
>        trace_ob_ide_read_blocks(arg1, arg2, arg3);
>        break;
>
>    default:
>        break;
>   }
> }
>
> ---
>  Makefile.objs     |   15 +++++++++++-
>  configure         |    9 +++++++-
>  guest-trace.h     |    3 ++
>  hw/fw_cfg.c       |   31 +++++++++++++++++++++++++++
>  hw/fw_cfg.h       |   10 ++++++--
>  scripts/tracetool |   60 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>  6 files changed, 120 insertions(+), 8 deletions(-)
>  create mode 100644 guest-trace.h

The ability to trace from the guest can be handy, so I think we should
have this feature.  Please add documentation on how to hook it up
(e.g. how people would use this for other firmware/guest code and/or
other architectures).

Guest and QEMU need to agree on event IDs.  The guest code needs to be
built with QEMU and they may not function with other QEMU builds or
guest builds.  This is fine for development but not feasible when QEMU
and the guest code are built or provided separately.

I suggest we merge this as a development feature that can be used when
bringing up new architectures, debugging guest code, or for some types
of performance work.  This feature falls under the Do-It-Yourself
area, where things could break relatively easy but developers who wish
to use it should be able to get it working in their area.

> +linetog_all()
> +{
> +    local name args argc arg
> +    name=$(get_name "$1")
> +    argc=$(get_argc "$1")
> +    fieldno=1

local fieldno

Stefan