Re: [Qemu-devel] [PATCH 0/3] scripts/qemu-gdb: Add event tracing support

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Thu, May 14, 2015 at 05:43:52PM +0100, Peter Maydell wrote:
> This patchset adds support for two new commands to our
> gdb scripts, which allow dynamically enabling and disabling
> tracing of events, like this:
> 
> (gdb) source scripts/qemu-gdb.py 
> (gdb) qemu trace-enable translate_block
> Enabled trace event translate_block
> Breakpoint 1 at 0xb634f: file ../trace/generated-tracers.h, line 4734.
> (gdb) run
> [...]
> translate_block: tb:0x7fffc69ce010, pc:0x40000000, tb_code:0x7fffd39ce000
> translate_block: tb:0x7fffc69ce078, pc:0x40010000, tb_code:0x7fffd39ce140
> translate_block: tb:0x7fffc69ce0e0, pc:0x40010034, tb_code:0x7fffd39ce180
> translate_block: tb:0x7fffc69ce148, pc:0x40013700, tb_code:0x7fffd39ce1d0
> translate_block: tb:0x7fffc69ce1b0, pc:0x40013710, tb_code:0x7fffd39ce270
> translate_block: tb:0x7fffc69ce218, pc:0x4001003c, tb_code:0x7fffd39ce310
> [etc]
> 
> This works by setting custom breakpoints on the stub functions
> trace_<eventname> that the null tracing backend creates. It
> probably doesn't work with an optimised build, but on the other
> hand because it's purely implemented within gdb you can use a
> tool like 'rr' (http://rr-project.org/) to record a run with no
> tracing enabled and then turn the tracing on and off as you desire
> during the replay.
> 
> Patches one and two do some initial splitting of qemu-gdb.py into
> separate modules just to keep it from growing unhelpfully large.
> 
> -- PMM
> 
> 
> Peter Maydell (3):
>   scripts/qemu-gdb: Split MtreeCommand into its own module
>   scripts/qemu-gdb: Split CoroutineCommand into its own file
>   scripts/qemu-gdb: Add support for printing trace events
> 
>  scripts/qemu-gdb.py          | 144 +++------------------------------
>  scripts/qemugdb/__init__.py  |  28 +++++++
>  scripts/qemugdb/coroutine.py |  91 +++++++++++++++++++++
>  scripts/qemugdb/mtree.py     |  82 +++++++++++++++++++
>  scripts/qemugdb/trace.py     | 188 +++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 398 insertions(+), 135 deletions(-)
>  create mode 100644 scripts/qemugdb/__init__.py
>  create mode 100644 scripts/qemugdb/coroutine.py
>  create mode 100644 scripts/qemugdb/mtree.py
>  create mode 100644 scripts/qemugdb/trace.py

Happy with this series although I'm not sure if it's needed since GDB
has static probes support for our SystemTap/DTrace tracepoints.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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