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5a0d9050db
Disable newly created kprobe events by default, not to disturb another user using ftrace. "Disturb" means when someone is using ftrace and another user tries to use perf-tools, (in near future) if he defines new kprobe event via perf-tools, then new events will mess up the frace buffer. Fix this to allow proper and transparent kprobes events concurrent usage between ftrace users and perf users. Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com> Acked-by: Steven Rostedt <rostedt@goodmis.org> Cc: Jim Keniston <jkenisto@us.ibm.com> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Frank Ch. Eigler <fche@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Jason Baron <jbaron@redhat.com> Cc: K.Prasad <prasad@linux.vnet.ibm.com> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Li Zefan <lizf@cn.fujitsu.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Cc: Tom Zanussi <tzanussi@gmail.com> LKML-Reference: <20090914204937.18779.59422.stgit@dhcp-100-2-132.bos.redhat.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
153 lines
6.0 KiB
Plaintext
153 lines
6.0 KiB
Plaintext
Kprobe-based Event Tracer
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=========================
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Documentation is written by Masami Hiramatsu
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Overview
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--------
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This tracer is similar to the events tracer which is based on Tracepoint
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infrastructure. Instead of Tracepoint, this tracer is based on kprobes(kprobe
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and kretprobe). It probes anywhere where kprobes can probe(this means, all
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functions body except for __kprobes functions).
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Unlike the function tracer, this tracer can probe instructions inside of
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kernel functions. It allows you to check which instruction has been executed.
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Unlike the Tracepoint based events tracer, this tracer can add and remove
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probe points on the fly.
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Similar to the events tracer, this tracer doesn't need to be activated via
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current_tracer, instead of that, just set probe points via
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/sys/kernel/debug/tracing/kprobe_events. And you can set filters on each
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probe events via /sys/kernel/debug/tracing/events/kprobes/<EVENT>/filter.
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Synopsis of kprobe_events
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-------------------------
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p[:[GRP/]EVENT] SYMBOL[+offs]|MEMADDR [FETCHARGS] : Set a probe
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r[:[GRP/]EVENT] SYMBOL[+0] [FETCHARGS] : Set a return probe
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GRP : Group name. If omitted, use "kprobes" for it.
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EVENT : Event name. If omitted, the event name is generated
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based on SYMBOL+offs or MEMADDR.
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SYMBOL[+offs] : Symbol+offset where the probe is inserted.
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MEMADDR : Address where the probe is inserted.
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FETCHARGS : Arguments. Each probe can have up to 128 args.
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%REG : Fetch register REG
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sN : Fetch Nth entry of stack (N >= 0)
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sa : Fetch stack address.
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@ADDR : Fetch memory at ADDR (ADDR should be in kernel)
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@SYM[+|-offs] : Fetch memory at SYM +|- offs (SYM should be a data symbol)
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aN : Fetch function argument. (N >= 0)(*)
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rv : Fetch return value.(**)
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ra : Fetch return address.(**)
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+|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(***)
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NAME=FETCHARG: Set NAME as the argument name of FETCHARG.
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(*) aN may not correct on asmlinkaged functions and at the middle of
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function body.
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(**) only for return probe.
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(***) this is useful for fetching a field of data structures.
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Per-Probe Event Filtering
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-------------------------
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Per-probe event filtering feature allows you to set different filter on each
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probe and gives you what arguments will be shown in trace buffer. If an event
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name is specified right after 'p:' or 'r:' in kprobe_events, the tracer adds
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an event under tracing/events/kprobes/<EVENT>, at the directory you can see
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'id', 'enabled', 'format' and 'filter'.
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enabled:
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You can enable/disable the probe by writing 1 or 0 on it.
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format:
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This shows the format of this probe event.
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filter:
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You can write filtering rules of this event.
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id:
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This shows the id of this probe event.
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Event Profiling
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---------------
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You can check the total number of probe hits and probe miss-hits via
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/sys/kernel/debug/tracing/kprobe_profile.
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The first column is event name, the second is the number of probe hits,
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the third is the number of probe miss-hits.
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Usage examples
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--------------
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To add a probe as a new event, write a new definition to kprobe_events
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as below.
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echo p:myprobe do_sys_open dfd=a0 filename=a1 flags=a2 mode=a3 > /sys/kernel/debug/tracing/kprobe_events
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This sets a kprobe on the top of do_sys_open() function with recording
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1st to 4th arguments as "myprobe" event. As this example shows, users can
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choose more familiar names for each arguments.
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echo r:myretprobe do_sys_open rv ra >> /sys/kernel/debug/tracing/kprobe_events
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This sets a kretprobe on the return point of do_sys_open() function with
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recording return value and return address as "myretprobe" event.
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You can see the format of these events via
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/sys/kernel/debug/tracing/events/kprobes/<EVENT>/format.
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cat /sys/kernel/debug/tracing/events/kprobes/myprobe/format
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name: myprobe
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ID: 75
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format:
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field:unsigned short common_type; offset:0; size:2;
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field:unsigned char common_flags; offset:2; size:1;
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field:unsigned char common_preempt_count; offset:3; size:1;
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field:int common_pid; offset:4; size:4;
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field:int common_tgid; offset:8; size:4;
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field: unsigned long ip; offset:16;tsize:8;
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field: int nargs; offset:24;tsize:4;
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field: unsigned long dfd; offset:32;tsize:8;
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field: unsigned long filename; offset:40;tsize:8;
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field: unsigned long flags; offset:48;tsize:8;
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field: unsigned long mode; offset:56;tsize:8;
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print fmt: "(%lx) dfd=%lx filename=%lx flags=%lx mode=%lx", REC->ip, REC->dfd, REC->filename, REC->flags, REC->mode
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You can see that the event has 4 arguments as in the expressions you specified.
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echo > /sys/kernel/debug/tracing/kprobe_events
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This clears all probe points.
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Right after definition, each event is disabled by default. For tracing these
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events, you need to enable it.
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echo 1 > /sys/kernel/debug/tracing/events/kprobes/myprobe/enable
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echo 1 > /sys/kernel/debug/tracing/events/kprobes/myretprobe/enable
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And you can see the traced information via /sys/kernel/debug/tracing/trace.
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cat /sys/kernel/debug/tracing/trace
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# tracer: nop
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#
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# TASK-PID CPU# TIMESTAMP FUNCTION
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# | | | | |
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<...>-1447 [001] 1038282.286875: myprobe: (do_sys_open+0x0/0xd6) dfd=3 filename=7fffd1ec4440 flags=8000 mode=0
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<...>-1447 [001] 1038282.286878: myretprobe: (sys_openat+0xc/0xe <- do_sys_open) rv=fffffffffffffffe ra=ffffffff81367a3a
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<...>-1447 [001] 1038282.286885: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=40413c flags=8000 mode=1b6
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<...>-1447 [001] 1038282.286915: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) rv=3 ra=ffffffff81367a3a
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<...>-1447 [001] 1038282.286969: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=4041c6 flags=98800 mode=10
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<...>-1447 [001] 1038282.286976: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) rv=3 ra=ffffffff81367a3a
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Each line shows when the kernel hits an event, and <- SYMBOL means kernel
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returns from SYMBOL(e.g. "sys_open+0x1b/0x1d <- do_sys_open" means kernel
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returns from do_sys_open to sys_open+0x1b).
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