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2023-12-11 d2ccde1c8e90d38cee87a1b0309ad2827f3fd30d

 kernel/Documentation/trace/uprobetracer.rst
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 However unlike kprobe-event tracer, the uprobe event interface expects the
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 user to calculate the offset of the probepoint in the object.
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+You can also use /sys/kernel/debug/tracing/dynamic_events instead of
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+uprobe_events. That interface will provide unified access to other
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+dynamic events too.
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+
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 Synopsis of uprobe_tracer
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 -------------------------
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 ::
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   p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe
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   r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe)
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+  p[:[GRP/]EVENT] PATH:OFFSET%return [FETCHARGS] : Set a return uprobe (uretprobe)
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   -:[GRP/]EVENT                           : Clear uprobe or uretprobe event
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   GRP           : Group name. If omitted, "uprobes" is the default value.
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                   on PATH+OFFSET.
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   PATH          : Path to an executable or a library.
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   OFFSET        : Offset where the probe is inserted.
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+  OFFSET%return : Offset where the return 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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    @+OFFSET	: Fetch memory at OFFSET (OFFSET from same file as PATH)
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    $stackN	: Fetch Nth entry of stack (N >= 0)
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    $stack	: Fetch stack address.
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-   $retval	: Fetch return value.(*)
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+   $retval	: Fetch return value.(\*1)
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    $comm	: Fetch current task comm.
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-   +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
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+   +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*2)(\*3)
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+   \IMM		: Store an immediate value to the argument.
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    NAME=FETCHARG     : Set NAME as the argument name of FETCHARG.
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    FETCHARG:TYPE     : Set TYPE as the type of FETCHARG. Currently, basic types
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 		       (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types
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 		       (x8/x16/x32/x64), "string" and bitfield are supported.
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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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+  (\*1) only for return probe.
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+  (\*2) this is useful for fetching a field of data structures.
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+  (\*3) Unlike kprobe event, "u" prefix will just be ignored, becuse uprobe
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+        events can access only user-space memory.
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 Types
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 -----
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@@ -69,10 +78,9 @@
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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/uprobe_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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+You can check the total number of probe hits per event via
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+/sys/kernel/debug/tracing/uprobe_profile. The first column is the filename,
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+the second is the event name, the third is the number of probe hits.
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 Usage examples
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 --------------
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     # echo 1 > events/uprobes/enable
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-Lets disable the event after sleeping for some time.
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+Lets start tracing, sleep for some time and stop tracing.
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 ::
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+    # echo 1 > tracing_on
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     # sleep 20
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+    # echo 0 > tracing_on
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+
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+Also, you can disable the event by::
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     # echo 0 > events/uprobes/enable
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 And you can see the traced information via /sys/kernel/debug/tracing/trace.