--- /dev/null
+=========================================
+Uprobe-tracer: Uprobe-based Event Tracing
+=========================================
+
+:Author: Srikar Dronamraju
+
+
+Overview
+--------
+Uprobe based trace events are similar to kprobe based trace events.
+To enable this feature, build your kernel with CONFIG_UPROBE_EVENTS=y.
+
+Similar to the kprobe-event tracer, this doesn't need to be activated via
+current_tracer. Instead of that, add probe points via
+/sys/kernel/debug/tracing/uprobe_events, and enable it 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.
+
+Synopsis of uprobe_tracer
+-------------------------
+::
+
+ p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe
+ r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe)
+ -:[GRP/]EVENT : Clear uprobe or uretprobe event
+
+ GRP : Group name. If omitted, "uprobes" is the default value.
+ EVENT : Event name. If omitted, the event name is generated based
+ on PATH+OFFSET.
+ PATH : Path to an executable or a library.
+ OFFSET : Offset where the probe is inserted.
+
+ FETCHARGS : Arguments. Each probe can have up to 128 args.
+ %REG : Fetch register REG
+ @ADDR : Fetch memory at ADDR (ADDR should be in userspace)
+ @+OFFSET : Fetch memory at OFFSET (OFFSET from same file as PATH)
+ $stackN : Fetch Nth entry of stack (N >= 0)
+ $stack : Fetch stack address.
+ $retval : Fetch return value.(*)
+ $comm : Fetch current task comm.
+ +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
+ NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
+ FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
+ (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types
+ (x8/x16/x32/x64), "string" and bitfield are supported.
+
+ (*) only for return probe.
+ (**) this is useful for fetching a field of data structures.
+
+Types
+-----
+Several types are supported for fetch-args. Uprobe tracer will access memory
+by given type. Prefix 's' and 'u' means those types are signed and unsigned
+respectively. 'x' prefix implies it is unsigned. Traced arguments are shown
+in decimal ('s' and 'u') or hexadecimal ('x'). Without type casting, 'x32'
+or 'x64' is used depends on the architecture (e.g. x86-32 uses x32, and
+x86-64 uses x64).
+String type is a special type, which fetches a "null-terminated" string from
+user space.
+Bitfield is another special type, which takes 3 parameters, bit-width, bit-
+offset, and container-size (usually 32). The syntax is::
+
+ b<bit-width>@<bit-offset>/<container-size>
+
+For $comm, the default type is "string"; any other type is invalid.
+
+
+Event Profiling
+---------------
+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 third is the number of probe miss-hits.
+
+Usage examples
+--------------
+ * 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_bash_0x4245c0' >> /sys/kernel/debug/tracing/uprobe_events
+
+ * Print out the events that are registered::
+
+ cat /sys/kernel/debug/tracing/uprobe_events
+
+ * Clear all events::
+
+ 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
+ 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 uprobe would be::
+
+ # echo 'p:zfree_entry /bin/zsh:0x46420 %ip %ax' > uprobe_events
+
+And the same for the uretprobe would be::
+
+ # echo 'r:zfree_exit /bin/zsh:0x46420 %ip %ax' >> uprobe_events
+
+.. 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/zfree_entry /bin/zsh:0x00046420 arg1=%ip arg2=%ax
+ r:uprobes/zfree_exit /bin/zsh:0x00046420 arg1=%ip arg2=%ax
+
+Format of events can be seen by viewing the file events/uprobes/zfree_entry/format.
+::
+
+ # 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 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
+
+Right after definition, each event is disabled by default. For tracing these
+events, you need to enable it by::
+
+ # echo 1 > events/uprobes/enable
+
+Lets disable the event after sleeping for some time.
+::
+
+ # sleep 20
+ # echo 0 > events/uprobes/enable
+
+And you can see the traced information via /sys/kernel/debug/tracing/trace.
+::
+
+ # cat trace
+ # tracer: nop
+ #
+ # TASK-PID CPU# TIMESTAMP FUNCTION
+ # | | | | |
+ 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.
+++ /dev/null
- Uprobe-tracer: Uprobe-based Event Tracing
- =========================================
-
- Documentation written by Srikar Dronamraju
-
-
-Overview
---------
-Uprobe based trace events are similar to kprobe based trace events.
-To enable this feature, build your kernel with CONFIG_UPROBE_EVENTS=y.
-
-Similar to the kprobe-event tracer, this doesn't need to be activated via
-current_tracer. Instead of that, add probe points via
-/sys/kernel/debug/tracing/uprobe_events, and enable it 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.
-
-Synopsis of uprobe_tracer
--------------------------
- p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe
- r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe)
- -:[GRP/]EVENT : Clear uprobe or uretprobe event
-
- GRP : Group name. If omitted, "uprobes" is the default value.
- EVENT : Event name. If omitted, the event name is generated based
- on PATH+OFFSET.
- PATH : Path to an executable or a library.
- OFFSET : Offset where the probe is inserted.
-
- FETCHARGS : Arguments. Each probe can have up to 128 args.
- %REG : Fetch register REG
- @ADDR : Fetch memory at ADDR (ADDR should be in userspace)
- @+OFFSET : Fetch memory at OFFSET (OFFSET from same file as PATH)
- $stackN : Fetch Nth entry of stack (N >= 0)
- $stack : Fetch stack address.
- $retval : Fetch return value.(*)
- $comm : Fetch current task comm.
- +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
- NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
- FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
- (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types
- (x8/x16/x32/x64), "string" and bitfield are supported.
-
- (*) only for return probe.
- (**) this is useful for fetching a field of data structures.
-
-Types
------
-Several types are supported for fetch-args. Uprobe tracer will access memory
-by given type. Prefix 's' and 'u' means those types are signed and unsigned
-respectively. 'x' prefix implies it is unsigned. Traced arguments are shown
-in decimal ('s' and 'u') or hexadecimal ('x'). Without type casting, 'x32'
-or 'x64' is used depends on the architecture (e.g. x86-32 uses x32, and
-x86-64 uses x64).
-String type is a special type, which fetches a "null-terminated" string from
-user space.
-Bitfield is another special type, which takes 3 parameters, bit-width, bit-
-offset, and container-size (usually 32). The syntax is;
-
- b<bit-width>@<bit-offset>/<container-size>
-
-For $comm, the default type is "string"; any other type is invalid.
-
-
-Event Profiling
----------------
-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 third is the number of probe miss-hits.
-
-Usage examples
---------------
- * 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_bash_0x4245c0' >> /sys/kernel/debug/tracing/uprobe_events
-
- * Print out the events that are registered:
-
- cat /sys/kernel/debug/tracing/uprobe_events
-
- * Clear all events:
-
- 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
- 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 uprobe would be:
-
- # echo 'p:zfree_entry /bin/zsh:0x46420 %ip %ax' > uprobe_events
-
- And the same for the uretprobe would be:
-
- # echo 'r:zfree_exit /bin/zsh:0x46420 %ip %ax' >> uprobe_events
-
-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/zfree_entry /bin/zsh:0x00046420 arg1=%ip arg2=%ax
- r:uprobes/zfree_exit /bin/zsh:0x00046420 arg1=%ip arg2=%ax
-
-Format of events can be seen by viewing the file events/uprobes/zfree_entry/format
-
- # 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 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
-
-Right after definition, each event is disabled by default. For tracing these
-events, you need to enable it by:
-
- # echo 1 > events/uprobes/enable
-
-Lets disable the event after sleeping for some time.
-
- # sleep 20
- # echo 0 > events/uprobes/enable
-
-And you can see the traced information via /sys/kernel/debug/tracing/trace.
-
- # cat trace
- # tracer: nop
- #
- # TASK-PID CPU# TIMESTAMP FUNCTION
- # | | | | |
- 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.
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