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2024-02-20 ea08eeccae9297f7aabd2ef7f0c2517ac4549acc 
 kernel/Documentation/trace/kprobetrace.rst
....@@ -20,6 +20,9 @@
2020 /sys/kernel/debug/tracing/kprobe_events, and enable it via
2121 /sys/kernel/debug/tracing/events/kprobes/<EVENT>/enable.
2222 
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+You can also use /sys/kernel/debug/tracing/dynamic_events instead of
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+kprobe_events. That interface will provide unified access to other
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+dynamic events too.
2326 
2427 Synopsis of kprobe_events
2528 -------------------------
....@@ -27,6 +30,7 @@
2730 
2831   p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS]	: Set a probe
2932   r[MAXACTIVE][:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS]	: Set a return probe
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+  p:[GRP/]EVENT] [MOD:]SYM[+0]%return [FETCHARGS]	: Set a return probe
3034   -:[GRP/]EVENT						: Clear a probe
3135 
3236  GRP		: Group name. If omitted, use "kprobes" for it.
....@@ -34,10 +38,11 @@
3438 		  based on SYM+offs or MEMADDR.
3539  MOD		: Module name which has given SYM.
3640  SYM[+offs]	: Symbol+offset where the probe is inserted.
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+ SYM%return	: Return address of the symbol
3742  MEMADDR	: Address where the probe is inserted.
3843  MAXACTIVE	: Maximum number of instances of the specified function that
3944 		  can be probed simultaneously, or 0 for the default value
40
-		  as defined in Documentation/kprobes.txt section 1.3.1.
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+		  as defined in Documentation/trace/kprobes.rst section 1.3.1.
4146 
4247  FETCHARGS	: Arguments. Each probe can have up to 128 args.
4348   %REG		: Fetch register REG
....@@ -45,16 +50,21 @@
4550   @SYM[+|-offs]	: Fetch memory at SYM +|- offs (SYM should be a data symbol)
4651   $stackN	: Fetch Nth entry of stack (N >= 0)
4752   $stack	: Fetch stack address.
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-  $retval	: Fetch return value.(*)
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+  $argN		: Fetch the Nth function argument. (N >= 1) (\*1)
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+  $retval	: Fetch return value.(\*2)
4955   $comm		: Fetch current task comm.
50
-  +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
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+  +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*3)(\*4)
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+  \IMM		: Store an immediate value to the argument.
5158   NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
5259   FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
5360 		  (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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+		  (x8/x16/x32/x64), "string", "ustring" and bitfield
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+		  are supported.
5563 
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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 the probe on function entry (offs == 0).
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+  (\*2) only for return probe.
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+  (\*3) this is useful for fetching a field of data structures.
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+  (\*4) "u" means user-space dereference. See :ref:`user_mem_access`.
5868 
5969 Types
6070 -----
....@@ -64,16 +74,50 @@
6474 in decimal ('s' and 'u') or hexadecimal ('x'). Without type casting, 'x32'
6575 or 'x64' is used depends on the architecture (e.g. x86-32 uses x32, and
6676 x86-64 uses x64).
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+These value types can be an array. To record array data, you can add '[N]'
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+(where N is a fixed number, less than 64) to the base type.
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+E.g. 'x16[4]' means an array of x16 (2bytes hex) with 4 elements.
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+Note that the array can be applied to memory type fetchargs, you can not
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+apply it to registers/stack-entries etc. (for example, '$stack1:x8[8]' is
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+wrong, but '+8($stack):x8[8]' is OK.)
6783 String type is a special type, which fetches a "null-terminated" string from
6884 kernel space. This means it will fail and store NULL if the string container
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-has been paged out.
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+has been paged out. "ustring" type is an alternative of string for user-space.
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+See :ref:`user_mem_access` for more info..
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+The string array type is a bit different from other types. For other base
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+types, <base-type>[1] is equal to <base-type> (e.g. +0(%di):x32[1] is same
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+as +0(%di):x32.) But string[1] is not equal to string. The string type itself
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+represents "char array", but string array type represents "char * array".
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+So, for example, +0(%di):string[1] is equal to +0(+0(%di)):string.
7092 Bitfield is another special type, which takes 3 parameters, bit-width, bit-
7193 offset, and container-size (usually 32). The syntax is::
7294 
7395  b<bit-width>@<bit-offset>/<container-size>
7496 
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+Symbol type('symbol') is an alias of u32 or u64 type (depends on BITS_PER_LONG)
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+which shows given pointer in "symbol+offset" style.
7599 For $comm, the default type is "string"; any other type is invalid.
76100 
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+.. _user_mem_access:
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+
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+User Memory Access
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+------------------
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+Kprobe events supports user-space memory access. For that purpose, you can use
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+either user-space dereference syntax or 'ustring' type.
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+
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+The user-space dereference syntax allows you to access a field of a data
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+structure in user-space. This is done by adding the "u" prefix to the
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+dereference syntax. For example, +u4(%si) means it will read memory from the
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+address in the register %si offset by 4, and the memory is expected to be in
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+user-space. You can use this for strings too, e.g. +u0(%si):string will read
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+a string from the address in the register %si that is expected to be in user-
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+space. 'ustring' is a shortcut way of performing the same task. That is,
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++0(%si):ustring is equivalent to +u0(%si):string.
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+
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+Note that kprobe-event provides the user-memory access syntax but it doesn't
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+use it transparently. This means if you use normal dereference or string type
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+for user memory, it might fail, and may always fail on some archs. The user
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+has to carefully check if the target data is in kernel or user space.
77121 
78122 Per-Probe Event Filtering
79123 -------------------------
....@@ -105,6 +149,20 @@
105149 /sys/kernel/debug/tracing/kprobe_profile.
106150 The first column is event name, the second is the number of probe hits,
107151 the third is the number of probe miss-hits.
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+
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+Kernel Boot Parameter
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+---------------------
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+You can add and enable new kprobe events when booting up the kernel by
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+"kprobe_event=" parameter. The parameter accepts a semicolon-delimited
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+kprobe events, which format is similar to the kprobe_events.
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+The difference is that the probe definition parameters are comma-delimited
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+instead of space. For example, adding myprobe event on do_sys_open like below
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+
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+  p:myprobe do_sys_open dfd=%ax filename=%dx flags=%cx mode=+4($stack)
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+
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+should be below for kernel boot parameter (just replace spaces with comma)
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+
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+  p:myprobe,do_sys_open,dfd=%ax,filename=%dx,flags=%cx,mode=+4($stack)
108166 
109167 
110168 Usage examples
....@@ -171,6 +229,13 @@
171229   echo 1 > /sys/kernel/debug/tracing/events/kprobes/myprobe/enable
172230   echo 1 > /sys/kernel/debug/tracing/events/kprobes/myretprobe/enable
173231 
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+Use the following command to start tracing in an interval.
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+::
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+
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+    # echo 1 > tracing_on
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+    Open something...
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+    # echo 0 > tracing_on
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+
174239 And you can see the traced information via /sys/kernel/debug/tracing/trace.
175240 ::
176241 
....@@ -190,4 +255,3 @@
190255 Each line shows when the kernel hits an event, and <- SYMBOL means kernel
191256 returns from SYMBOL(e.g. "sys_open+0x1b/0x1d <- do_sys_open" means kernel
192257 returns from do_sys_open to sys_open+0x1b).
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-