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Linux/Documentation/trace/uprobetracer.rst

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Diff markup

Differences between /Documentation/trace/uprobetracer.rst (Version linux-6.12-rc7) and /Documentation/trace/uprobetracer.rst (Version linux-5.18.19)


  1 =========================================           1 =========================================
  2 Uprobe-tracer: Uprobe-based Event Tracing           2 Uprobe-tracer: Uprobe-based Event Tracing
  3 =========================================           3 =========================================
  4                                                     4 
  5 :Author: Srikar Dronamraju                          5 :Author: Srikar Dronamraju
  6                                                     6 
  7                                                     7 
  8 Overview                                            8 Overview
  9 --------                                            9 --------
 10 Uprobe based trace events are similar to kprob     10 Uprobe based trace events are similar to kprobe based trace events.
 11 To enable this feature, build your kernel with     11 To enable this feature, build your kernel with CONFIG_UPROBE_EVENTS=y.
 12                                                    12 
 13 Similar to the kprobe-event tracer, this doesn     13 Similar to the kprobe-event tracer, this doesn't need to be activated via
 14 current_tracer. Instead of that, add probe poi     14 current_tracer. Instead of that, add probe points via
 15 /sys/kernel/tracing/uprobe_events, and enable  !!  15 /sys/kernel/debug/tracing/uprobe_events, and enable it via
 16 /sys/kernel/tracing/events/uprobes/<EVENT>/ena !!  16 /sys/kernel/debug/tracing/events/uprobes/<EVENT>/enable.
 17                                                    17 
 18 However unlike kprobe-event tracer, the uprobe     18 However unlike kprobe-event tracer, the uprobe event interface expects the
 19 user to calculate the offset of the probepoint     19 user to calculate the offset of the probepoint in the object.
 20                                                    20 
 21 You can also use /sys/kernel/tracing/dynamic_e !!  21 You can also use /sys/kernel/debug/tracing/dynamic_events instead of
 22 uprobe_events. That interface will provide uni     22 uprobe_events. That interface will provide unified access to other
 23 dynamic events too.                                23 dynamic events too.
 24                                                    24 
 25 Synopsis of uprobe_tracer                          25 Synopsis of uprobe_tracer
 26 -------------------------                          26 -------------------------
 27 ::                                                 27 ::
 28                                                    28 
 29   p[:[GRP/][EVENT]] PATH:OFFSET [FETCHARGS] :  !!  29   p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe
 30   r[:[GRP/][EVENT]] PATH:OFFSET [FETCHARGS] :  !!  30   r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe)
 31   p[:[GRP/][EVENT]] PATH:OFFSET%return [FETCHA !!  31   p[:[GRP/]EVENT] PATH:OFFSET%return [FETCHARGS] : Set a return uprobe (uretprobe)
 32   -:[GRP/][EVENT]                           :  !!  32   -:[GRP/]EVENT                           : Clear uprobe or uretprobe event
 33                                                    33 
 34   GRP           : Group name. If omitted, "upr     34   GRP           : Group name. If omitted, "uprobes" is the default value.
 35   EVENT         : Event name. If omitted, the      35   EVENT         : Event name. If omitted, the event name is generated based
 36                   on PATH+OFFSET.                  36                   on PATH+OFFSET.
 37   PATH          : Path to an executable or a l     37   PATH          : Path to an executable or a library.
 38   OFFSET        : Offset where the probe is in     38   OFFSET        : Offset where the probe is inserted.
 39   OFFSET%return : Offset where the return prob     39   OFFSET%return : Offset where the return probe is inserted.
 40                                                    40 
 41   FETCHARGS     : Arguments. Each probe can ha     41   FETCHARGS     : Arguments. Each probe can have up to 128 args.
 42    %REG         : Fetch register REG               42    %REG         : Fetch register REG
 43    @ADDR        : Fetch memory at ADDR (ADDR s     43    @ADDR        : Fetch memory at ADDR (ADDR should be in userspace)
 44    @+OFFSET     : Fetch memory at OFFSET (OFFS     44    @+OFFSET     : Fetch memory at OFFSET (OFFSET from same file as PATH)
 45    $stackN      : Fetch Nth entry of stack (N      45    $stackN      : Fetch Nth entry of stack (N >= 0)
 46    $stack       : Fetch stack address.             46    $stack       : Fetch stack address.
 47    $retval      : Fetch return value.(\*1)         47    $retval      : Fetch return value.(\*1)
 48    $comm        : Fetch current task comm.         48    $comm        : Fetch current task comm.
 49    +|-[u]OFFS(FETCHARG) : Fetch memory at FETC     49    +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*2)(\*3)
 50    \IMM         : Store an immediate value to      50    \IMM         : Store an immediate value to the argument.
 51    NAME=FETCHARG     : Set NAME as the argumen     51    NAME=FETCHARG     : Set NAME as the argument name of FETCHARG.
 52    FETCHARG:TYPE     : Set TYPE as the type of     52    FETCHARG:TYPE     : Set TYPE as the type of FETCHARG. Currently, basic types
 53                        (u8/u16/u32/u64/s8/s16/     53                        (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types
 54                        (x8/x16/x32/x64), "stri     54                        (x8/x16/x32/x64), "string" and bitfield are supported.
 55                                                    55 
 56   (\*1) only for return probe.                     56   (\*1) only for return probe.
 57   (\*2) this is useful for fetching a field of     57   (\*2) this is useful for fetching a field of data structures.
 58   (\*3) Unlike kprobe event, "u" prefix will j !!  58   (\*3) Unlike kprobe event, "u" prefix will just be ignored, becuse uprobe
 59         events can access only user-space memo     59         events can access only user-space memory.
 60                                                    60 
 61 Types                                              61 Types
 62 -----                                              62 -----
 63 Several types are supported for fetch-args. Up     63 Several types are supported for fetch-args. Uprobe tracer will access memory
 64 by given type. Prefix 's' and 'u' means those      64 by given type. Prefix 's' and 'u' means those types are signed and unsigned
 65 respectively. 'x' prefix implies it is unsigne     65 respectively. 'x' prefix implies it is unsigned. Traced arguments are shown
 66 in decimal ('s' and 'u') or hexadecimal ('x').     66 in decimal ('s' and 'u') or hexadecimal ('x'). Without type casting, 'x32'
 67 or 'x64' is used depends on the architecture (     67 or 'x64' is used depends on the architecture (e.g. x86-32 uses x32, and
 68 x86-64 uses x64).                                  68 x86-64 uses x64).
 69 String type is a special type, which fetches a     69 String type is a special type, which fetches a "null-terminated" string from
 70 user space.                                        70 user space.
 71 Bitfield is another special type, which takes      71 Bitfield is another special type, which takes 3 parameters, bit-width, bit-
 72 offset, and container-size (usually 32). The s     72 offset, and container-size (usually 32). The syntax is::
 73                                                    73 
 74  b<bit-width>@<bit-offset>/<container-size>         74  b<bit-width>@<bit-offset>/<container-size>
 75                                                    75 
 76 For $comm, the default type is "string"; any o     76 For $comm, the default type is "string"; any other type is invalid.
 77                                                    77 
 78                                                    78 
 79 Event Profiling                                    79 Event Profiling
 80 ---------------                                    80 ---------------
 81 You can check the total number of probe hits p     81 You can check the total number of probe hits per event via
 82 /sys/kernel/tracing/uprobe_profile. The first  !!  82 /sys/kernel/debug/tracing/uprobe_profile. The first column is the filename,
 83 the second is the event name, the third is the     83 the second is the event name, the third is the number of probe hits.
 84                                                    84 
 85 Usage examples                                     85 Usage examples
 86 --------------                                     86 --------------
 87  * Add a probe as a new uprobe event, write a      87  * Add a probe as a new uprobe event, write a new definition to uprobe_events
 88    as below (sets a uprobe at an offset of 0x4     88    as below (sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash)::
 89                                                    89 
 90     echo 'p /bin/bash:0x4245c0' > /sys/kernel/ !!  90     echo 'p /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events
 91                                                    91 
 92  * Add a probe as a new uretprobe event::          92  * Add a probe as a new uretprobe event::
 93                                                    93 
 94     echo 'r /bin/bash:0x4245c0' > /sys/kernel/ !!  94     echo 'r /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events
 95                                                    95 
 96  * Unset registered event::                        96  * Unset registered event::
 97                                                    97 
 98     echo '-:p_bash_0x4245c0' >> /sys/kernel/tr !!  98     echo '-:p_bash_0x4245c0' >> /sys/kernel/debug/tracing/uprobe_events
 99                                                    99 
100  * Print out the events that are registered::     100  * Print out the events that are registered::
101                                                   101 
102     cat /sys/kernel/tracing/uprobe_events      !! 102     cat /sys/kernel/debug/tracing/uprobe_events
103                                                   103 
104  * Clear all events::                             104  * Clear all events::
105                                                   105 
106     echo > /sys/kernel/tracing/uprobe_events   !! 106     echo > /sys/kernel/debug/tracing/uprobe_events
107                                                   107 
108 Following example shows how to dump the instru    108 Following example shows how to dump the instruction pointer and %ax register
109 at the probed text address. Probe zfree functi    109 at the probed text address. Probe zfree function in /bin/zsh::
110                                                   110 
111     # cd /sys/kernel/tracing/                  !! 111     # cd /sys/kernel/debug/tracing/
112     # cat /proc/`pgrep zsh`/maps | grep /bin/z    112     # cat /proc/`pgrep zsh`/maps | grep /bin/zsh | grep r-xp
113     00400000-0048a000 r-xp 00000000 08:03 1309    113     00400000-0048a000 r-xp 00000000 08:03 130904 /bin/zsh
114     # objdump -T /bin/zsh | grep -w zfree         114     # objdump -T /bin/zsh | grep -w zfree
115     0000000000446420 g    DF .text  0000000000    115     0000000000446420 g    DF .text  0000000000000012  Base        zfree
116                                                   116 
117 0x46420 is the offset of zfree in object /bin/    117 0x46420 is the offset of zfree in object /bin/zsh that is loaded at
118 0x00400000. Hence the command to uprobe would     118 0x00400000. Hence the command to uprobe would be::
119                                                   119 
120     # echo 'p:zfree_entry /bin/zsh:0x46420 %ip    120     # echo 'p:zfree_entry /bin/zsh:0x46420 %ip %ax' > uprobe_events
121                                                   121 
122 And the same for the uretprobe would be::         122 And the same for the uretprobe would be::
123                                                   123 
124     # echo 'r:zfree_exit /bin/zsh:0x46420 %ip     124     # echo 'r:zfree_exit /bin/zsh:0x46420 %ip %ax' >> uprobe_events
125                                                   125 
126 .. note:: User has to explicitly calculate the    126 .. note:: User has to explicitly calculate the offset of the probe-point
127         in the object.                            127         in the object.
128                                                   128 
129 We can see the events that are registered by l    129 We can see the events that are registered by looking at the uprobe_events file.
130 ::                                                130 ::
131                                                   131 
132     # cat uprobe_events                           132     # cat uprobe_events
133     p:uprobes/zfree_entry /bin/zsh:0x00046420     133     p:uprobes/zfree_entry /bin/zsh:0x00046420 arg1=%ip arg2=%ax
134     r:uprobes/zfree_exit /bin/zsh:0x00046420 a    134     r:uprobes/zfree_exit /bin/zsh:0x00046420 arg1=%ip arg2=%ax
135                                                   135 
136 Format of events can be seen by viewing the fi    136 Format of events can be seen by viewing the file events/uprobes/zfree_entry/format.
137 ::                                                137 ::
138                                                   138 
139     # cat events/uprobes/zfree_entry/format       139     # cat events/uprobes/zfree_entry/format
140     name: zfree_entry                             140     name: zfree_entry
141     ID: 922                                       141     ID: 922
142     format:                                       142     format:
143          field:unsigned short common_type;        143          field:unsigned short common_type;         offset:0;  size:2; signed:0;
144          field:unsigned char common_flags;        144          field:unsigned char common_flags;         offset:2;  size:1; signed:0;
145          field:unsigned char common_preempt_co    145          field:unsigned char common_preempt_count; offset:3;  size:1; signed:0;
146          field:int common_pid;                    146          field:int common_pid;                     offset:4;  size:4; signed:1;
147          field:int common_padding;                147          field:int common_padding;                 offset:8;  size:4; signed:1;
148                                                   148 
149          field:unsigned long __probe_ip;          149          field:unsigned long __probe_ip;           offset:12; size:4; signed:0;
150          field:u32 arg1;                          150          field:u32 arg1;                           offset:16; size:4; signed:0;
151          field:u32 arg2;                          151          field:u32 arg2;                           offset:20; size:4; signed:0;
152                                                   152 
153     print fmt: "(%lx) arg1=%lx arg2=%lx", REC-    153     print fmt: "(%lx) arg1=%lx arg2=%lx", REC->__probe_ip, REC->arg1, REC->arg2
154                                                   154 
155 Right after definition, each event is disabled    155 Right after definition, each event is disabled by default. For tracing these
156 events, you need to enable it by::                156 events, you need to enable it by::
157                                                   157 
158     # echo 1 > events/uprobes/enable              158     # echo 1 > events/uprobes/enable
159                                                   159 
160 Lets start tracing, sleep for some time and st    160 Lets start tracing, sleep for some time and stop tracing.
161 ::                                                161 ::
162                                                   162 
163     # echo 1 > tracing_on                         163     # echo 1 > tracing_on
164     # sleep 20                                    164     # sleep 20
165     # echo 0 > tracing_on                         165     # echo 0 > tracing_on
166                                                   166 
167 Also, you can disable the event by::              167 Also, you can disable the event by::
168                                                   168 
169     # echo 0 > events/uprobes/enable              169     # echo 0 > events/uprobes/enable
170                                                   170 
171 And you can see the traced information via /sy !! 171 And you can see the traced information via /sys/kernel/debug/tracing/trace.
172 ::                                                172 ::
173                                                   173 
174     # cat trace                                   174     # cat trace
175     # tracer: nop                                 175     # tracer: nop
176     #                                             176     #
177     #           TASK-PID    CPU#    TIMESTAMP     177     #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
178     #              | |       |          |         178     #              | |       |          |         |
179                  zsh-24842 [006] 258544.995456    179                  zsh-24842 [006] 258544.995456: zfree_entry: (0x446420) arg1=446420 arg2=79
180                  zsh-24842 [007] 258545.000270    180                  zsh-24842 [007] 258545.000270: zfree_exit:  (0x446540 <- 0x446420) arg1=446540 arg2=0
181                  zsh-24842 [002] 258545.043929    181                  zsh-24842 [002] 258545.043929: zfree_entry: (0x446420) arg1=446420 arg2=79
182                  zsh-24842 [004] 258547.046129    182                  zsh-24842 [004] 258547.046129: zfree_exit:  (0x446540 <- 0x446420) arg1=446540 arg2=0
183                                                   183 
184 Output shows us uprobe was triggered for a pid    184 Output shows us uprobe was triggered for a pid 24842 with ip being 0x446420
185 and contents of ax register being 79. And uret    185 and contents of ax register being 79. And uretprobe was triggered with ip at
186 0x446540 with counterpart function entry at 0x    186 0x446540 with counterpart function entry at 0x446420.
                                                      

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