[PATCH v1 9/9] uretprobes: Documentation update
From: Anton Arapov
Date: Wed Apr 03 2013 - 12:09:23 EST
add the uretprobe syntax and update an example
Signed-off-by: Anton Arapov <anton@xxxxxxxxxx>
---
Documentation/trace/uprobetracer.txt | 114 ++++++++++++++++++++---------------
1 file changed, 67 insertions(+), 47 deletions(-)
diff --git a/Documentation/trace/uprobetracer.txt b/Documentation/trace/uprobetracer.txt
index 24ce682..d9c3e68 100644
--- a/Documentation/trace/uprobetracer.txt
+++ b/Documentation/trace/uprobetracer.txt
@@ -1,6 +1,8 @@
- Uprobe-tracer: Uprobe-based Event Tracing
- =========================================
- Documentation written by Srikar Dronamraju
+ Uprobe-tracer: Uprobe-based Event Tracing
+ =========================================
+
+ Documentation written by Srikar Dronamraju
+
Overview
--------
@@ -13,78 +15,94 @@ current_tracer. Instead of that, add probe points via
/sys/kernel/debug/tracing/events/uprobes/<EVENT>/enabled.
However unlike kprobe-event tracer, the uprobe event interface expects the
-user to calculate the offset of the probepoint in the object
+user to calculate the offset of the probepoint in the object.
Synopsis of uprobe_tracer
-------------------------
- p[:[GRP/]EVENT] PATH:SYMBOL[+offs] [FETCHARGS] : Set a probe
+ p[:[GRP/]EVENT] PATH:SYMBOL[+offs] [FETCHARGS] : Set a uprobe
+ r[:[GRP/]EVENT] PATH:SYMBOL[+offs] [FETCHARGS] : Set a return uprobe (uretprobe)
+ -:[GRP/]EVENT : Clear uprobe or uretprobe event
- GRP : Group name. If omitted, use "uprobes" for it.
- EVENT : Event name. If omitted, the event name is generated
- based on SYMBOL+offs.
- PATH : path to an executable or a library.
- SYMBOL[+offs] : Symbol+offset where the probe is inserted.
+ GRP : Group name. If omitted, "uprobes" is the default value.
+ EVENT : Event name. If omitted, the event name is generated based
+ on SYMBOL+offs.
+ PATH : Path to an executable or a library.
+ SYMBOL[+offs] : Symbol+offset where the probe is inserted.
- FETCHARGS : Arguments. Each probe can have up to 128 args.
- %REG : Fetch register REG
+ FETCHARGS : Arguments. Each probe can have up to 128 args.
+ %REG : Fetch register REG
Event Profiling
---------------
- You can check the total number of probe hits and probe miss-hits via
+You can check the total number of probe hits and probe miss-hits via
/sys/kernel/debug/tracing/uprobe_profile.
- The first column is event name, the second is the number of probe hits,
+The first column is event name, the second is the number of probe hits,
the third is the number of probe miss-hits.
Usage examples
--------------
-To add a probe as a new event, write a new definition to uprobe_events
-as below.
+ * Add a probe as a new uprobe event, write a new definition to uprobe_events
+as below: (sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash)
+
+ echo 'p: /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events
+
+ * Add a probe as a new uretprobe event:
+
+ echo 'r: /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events
+
+ * Unset registered event:
- echo 'p: /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events
+ echo '-:bash_0x4245c0' >> /sys/kernel/debug/tracing/uprobe_events
- This sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash
+ * Print out the events that are registered:
- echo > /sys/kernel/debug/tracing/uprobe_events
+ cat /sys/kernel/debug/tracing/uprobe_events
- This clears all probe points.
+ * Clear all events:
-The following example shows how to dump the instruction pointer and %ax
-a register at the probed text address. Here we are trying to probe
-function zfree in /bin/zsh
+ echo > /sys/kernel/debug/tracing/uprobe_events
+
+Following example shows how to dump the instruction pointer and %ax register
+at the probed text address. Probe zfree function in /bin/zsh:
# cd /sys/kernel/debug/tracing/
- # cat /proc/`pgrep zsh`/maps | grep /bin/zsh | grep r-xp
+ # cat /proc/`pgrep zsh`/maps | grep /bin/zsh | grep r-xp
00400000-0048a000 r-xp 00000000 08:03 130904 /bin/zsh
# objdump -T /bin/zsh | grep -w zfree
0000000000446420 g DF .text 0000000000000012 Base zfree
-0x46420 is the offset of zfree in object /bin/zsh that is loaded at
-0x00400000. Hence the command to probe would be :
+ 0x46420 is the offset of zfree in object /bin/zsh that is loaded at
+ 0x00400000. Hence the command to uprobe would be:
+
+ # echo 'p:zfree_entry /bin/zsh:0x46420 %ip %ax' > uprobe_events
+
+ And the same for the uretprobe would be:
- # echo 'p /bin/zsh:0x46420 %ip %ax' > uprobe_events
+ # echo 'r:zfree_exit /bin/zsh:0x46420 %ip %ax' >> uprobe_events
-Please note: User has to explicitly calculate the offset of the probepoint
+Please note: User has to explicitly calculate the offset of the probe-point
in the object. We can see the events that are registered by looking at the
uprobe_events file.
# cat uprobe_events
- p:uprobes/p_zsh_0x46420 /bin/zsh:0x00046420 arg1=%ip arg2=%ax
+ p:uprobes/zfree_entry /bin/zsh:0x00046420 arg1=%ip arg2=%ax
+ r:uprobes/zfree_exit /bin/zsh:0x00046420 arg1=%ip arg2=%ax
-The format of events can be seen by viewing the file events/uprobes/p_zsh_0x46420/format
+Format of events can be seen by viewing the file events/uprobes/zfree_entry/format
- # cat events/uprobes/p_zsh_0x46420/format
- name: p_zsh_0x46420
+ # cat events/uprobes/zfree_entry/format
+ name: zfree_entry
ID: 922
format:
- field:unsigned short common_type; offset:0; size:2; signed:0;
- field:unsigned char common_flags; offset:2; size:1; signed:0;
- field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
- field:int common_pid; offset:4; size:4; signed:1;
- field:int common_padding; offset:8; size:4; signed:1;
+ field:unsigned short common_type; offset:0; size:2; signed:0;
+ field:unsigned char common_flags; offset:2; size:1; signed:0;
+ field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
+ field:int common_pid; offset:4; size:4; signed:1;
+ field:int common_padding; offset:8; size:4; signed:1;
- field:unsigned long __probe_ip; offset:12; size:4; signed:0;
- field:u32 arg1; offset:16; size:4; signed:0;
- field:u32 arg2; offset:20; size:4; signed:0;
+ field:unsigned long __probe_ip; offset:12; size:4; signed:0;
+ field:u32 arg1; offset:16; size:4; signed:0;
+ field:u32 arg2; offset:20; size:4; signed:0;
print fmt: "(%lx) arg1=%lx arg2=%lx", REC->__probe_ip, REC->arg1, REC->arg2
@@ -94,6 +112,7 @@ Right after definition, each event is disabled by default. For tracing these
# echo 1 > events/uprobes/enable
Lets disable the event after sleeping for some time.
+
# sleep 20
# echo 0 > events/uprobes/enable
@@ -104,10 +123,11 @@ And you can see the traced information via /sys/kernel/debug/tracing/trace.
#
# TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | |
- zsh-24842 [006] 258544.995456: p_zsh_0x46420: (0x446420) arg1=446421 arg2=79
- zsh-24842 [007] 258545.000270: p_zsh_0x46420: (0x446420) arg1=446421 arg2=79
- zsh-24842 [002] 258545.043929: p_zsh_0x46420: (0x446420) arg1=446421 arg2=79
- zsh-24842 [004] 258547.046129: p_zsh_0x46420: (0x446420) arg1=446421 arg2=79
-
-Each line shows us probes were triggered for a pid 24842 with ip being
-0x446421 and contents of ax register being 79.
+ zsh-24842 [006] 258544.995456: zfree_entry: (0x446420) arg1=446420 arg2=79
+ zsh-24842 [007] 258545.000270: zfree_exit: (0x446540 <- 0x446420) arg1=446540 arg2=0
+ zsh-24842 [002] 258545.043929: zfree_entry: (0x446420) arg1=446420 arg2=79
+ zsh-24842 [004] 258547.046129: zfree_exit: (0x446540 <- 0x446420) arg1=446540 arg2=0
+
+Output shows us uprobe was triggered for a pid 24842 with ip being 0x446420
+and contents of ax register being 79. And uretprobe was triggered with ip at
+0x446540 with counterpart function entry at 0x446420.
--
1.8.1.4
--
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