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Re: [PATCH -tip v5 0/7] tracing: kprobe-based event tracer and x86 instruction decoder
- From: Ingo Molnar <mingo at elte dot hu>
- To: Masami Hiramatsu <mhiramat at redhat dot com>
- Cc: Steven Rostedt <rostedt at goodmis dot org>, lkml <linux-kernel at vger dot kernel dot org>, Avi Kivity <avi at redhat dot com>, "H. Peter Anvin" <hpa at zytor dot com>, Frederic Weisbecker <fweisbec at gmail dot com>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Andrew Morton <akpm at linux-foundation dot org>, Andi Kleen <andi at firstfloor dot org>, Jim Keniston <jkenisto at us dot ibm dot com>, "K.Prasad" <prasad at linux dot vnet dot ibm dot com>, KOSAKI Motohiro <kosaki dot motohiro at jp dot fujitsu dot com>, systemtap <systemtap at sources dot redhat dot com>, kvm <kvm at vger dot kernel dot org>
- Date: Sat, 9 May 2009 06:43:02 +0200
- Subject: Re: [PATCH -tip v5 0/7] tracing: kprobe-based event tracer and x86 instruction decoder
- References: <20090509004829.5505.38720.stgit@localhost.localdomain>
* Masami Hiramatsu <mhiramat@redhat.com> wrote:
> Hi,
>
> Here are the patches of kprobe-based event tracer for x86, version
> 5, which allows you to probe various kernel events through ftrace
> interface.
>
> This version supports only x86(-32/-64) (but porting it on other
> arch just needs kprobes/kretprobes and register and stack access
> APIs).
>
> This patchset also includes x86(-64) instruction decoder which
> supports non-SSE/FP opcodes and includes x86 opcode map. I think
> it will be possible to share this opcode map with KVM's decoder.
>
> This series can be applied on the latest linux-2.6-tip tree.
>
> This patchset includes following changes:
> - Add x86 instruction decoder [1/7]
> - Check insertion point safety in kprobe [2/7]
> - Cleanup fix_riprel() with insn decoder [3/7]
> - Add kprobe-tracer plugin [4/7]
> - Fix kernel_trap_sp() on x86 according to systemtap runtime. [5/7]
> - Add arch-dep register and stack fetching functions [6/7]
> - Support fetching various status (register/stack/memory/etc.) [7/7]
>
> Future items:
> - .init function tracing support.
> - Support primitive types(long, ulong, int, uint, etc) for args.
Ok, this looks pretty complete already.
Two high-level comments:
- There's no self-test - would it be possible to add one? See
trace_selftest* in kernel/trace/
- No generic integration.
It would be nice if these ops:
> E.g.
> echo p do_sys_open a0 a1 a2 a3 > /debug/tracing/kprobe_events
>
> This sets a kprobe on the top of do_sys_open() function with recording
> 1st to 4th arguments.
>
> echo r do_sys_open rv rp >> /debug/tracing/kprobe_events
were just generally available in just about any other tracer - a bit
like the event tracer.
It would also be nice to use the 'function attributes' facilities of
the function tracer, combined with a new special syntax of the
function-filter regex parser, to enable the recovery of return
values (or the call arguments), for selected set of functions.
For example, today we can already do things like:
echo 'sys_read:traceon:4' > /debug/tracing/set_ftrace_filter
for 'trace triggers': the above will trigger tracing to be enabled
on the entry of sys_read(), 4 times.
Likewise, something like:
echo 'sys_read:args' > /debug/tracing/set_ftrace_filter
echo 'sys_read:return' > /debug/tracing/set_ftrace_filter
Could activate kprobes based argument and return-value tracing.
Ingo