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authorDonglin Peng <dolinux.peng@gmail.com>2023-02-21 02:52:42 +0300
committerMasami Hiramatsu (Google) <mhiramat@kernel.org>2023-02-21 02:52:42 +0300
commit8478cca1e3abd183f309cd9c2491f484acf5d377 (patch)
tree22623d22350cc9f938a59ddc85b87da6bbb8ffdd /Documentation/trace
parent96cd93af794cf3ef83ae1ad7291160029d7b525e (diff)
downloadlinux-8478cca1e3abd183f309cd9c2491f484acf5d377.tar.xz
tracing/probe: add a char type to show the character value of traced arguments
There are scenes that we want to show the character value of traced arguments other than a decimal or hexadecimal or string value for debug convinience. I add a new type named 'char' to do it and a new test case file named 'kprobe_args_char.tc' to do selftest for char type. For example: The to be traced function is 'void demo_func(char type, char *name);', we can add a kprobe event as follows to show argument values as we want: echo 'p:myprobe demo_func $arg1:char +0($arg2):char[5]' > kprobe_events we will get the following trace log: ... myprobe: (demo_func+0x0/0x29) arg1='A' arg2={'b','p','f','1',''} Link: https://lore.kernel.org/all/20221219110613.367098-1-dolinux.peng@gmail.com/ Signed-off-by: Donglin Peng <dolinux.peng@gmail.com> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Reported-by: kernel test robot <lkp@intel.com> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Diffstat (limited to 'Documentation/trace')
-rw-r--r--Documentation/trace/kprobetrace.rst3
1 files changed, 2 insertions, 1 deletions
diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst
index 08a2a6a3782f..ef223b8ad6d5 100644
--- a/Documentation/trace/kprobetrace.rst
+++ b/Documentation/trace/kprobetrace.rst
@@ -58,7 +58,7 @@ Synopsis of kprobe_events
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", "ustring", "symbol", "symstr"
+ (x8/x16/x32/x64), "char", "string", "ustring", "symbol", "symstr"
and bitfield are supported.
(\*1) only for the probe on function entry (offs == 0).
@@ -80,6 +80,7 @@ E.g. 'x16[4]' means an array of x16 (2bytes hex) with 4 elements.
Note that the array can be applied to memory type fetchargs, you can not
apply it to registers/stack-entries etc. (for example, '$stack1:x8[8]' is
wrong, but '+8($stack):x8[8]' is OK.)
+Char type can be used to show the character value of traced arguments.
String type is a special type, which fetches a "null-terminated" string from
kernel space. This means it will fail and store NULL if the string container
has been paged out. "ustring" type is an alternative of string for user-space.