Re: [PATCH v6] tracing/probe: add a char type to show the character value of traced arguments

[Steven Rostedt]

Looking back at emails that happened when I was off ;-)

Masami, what's you thoughts about this patch?

-- Steve


On Mon, 19 Dec 2022 03:06:13 -0800
Donglin Peng <dolinux.peng@xxxxxxxxx> wrote:

> 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',''}
> 
> Signed-off-by: Donglin Peng <dolinux.peng@xxxxxxxxx>
> Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> ---
> Changes in v6:
>  - change "\'%c\'" to "'%c'" in trace_probe.c
> 
> Changes in v5:
>  - wrap the output character with single quotes
>  - add a test case named kprobe_args_char.tc to do selftest
> 
> Changes in v4:
>  - update the example in the commit log
> 
> Changes in v3:
>  - update readme_msg
> 
> Changes in v2:
>  - fix build warnings reported by kernel test robot
>  - modify commit log
> ---
>  Documentation/trace/kprobetrace.rst           |  3 +-
>  kernel/trace/trace.c                          |  2 +-
>  kernel/trace/trace_probe.c                    |  2 +
>  kernel/trace/trace_probe.h                    |  1 +
>  .../ftrace/test.d/kprobe/kprobe_args_char.tc  | 47 +++++++++++++++++++
>  5 files changed, 53 insertions(+), 2 deletions(-)
>  create mode 100644 tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_char.tc
> 
> diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst
> index 4274cc6a2f94..007972a3c5c4 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" and bitfield
> +		  (x8/x16/x32/x64), "char", "string", "ustring" 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.
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 6d7ef130f57e..c602081e64c8 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -5615,7 +5615,7 @@ static const char readme_msg[] =
>  	"\t           $stack<index>, $stack, $retval, $comm,\n"
>  #endif
>  	"\t           +|-[u]<offset>(<fetcharg>), \\imm-value, \\\"imm-string\"\n"
> -	"\t     type: s8/16/32/64, u8/16/32/64, x8/16/32/64, string, symbol,\n"
> +	"\t     type: s8/16/32/64, u8/16/32/64, x8/16/32/64, char, string, symbol,\n"
>  	"\t           b<bit-width>@<bit-offset>/<container-size>, ustring,\n"
>  	"\t           <type>\\[<array-size>\\]\n"
>  #ifdef CONFIG_HIST_TRIGGERS
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index bb2f95d7175c..794a21455396 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -50,6 +50,7 @@ DEFINE_BASIC_PRINT_TYPE_FUNC(x8,  u8,  "0x%x")
>  DEFINE_BASIC_PRINT_TYPE_FUNC(x16, u16, "0x%x")
>  DEFINE_BASIC_PRINT_TYPE_FUNC(x32, u32, "0x%x")
>  DEFINE_BASIC_PRINT_TYPE_FUNC(x64, u64, "0x%Lx")
> +DEFINE_BASIC_PRINT_TYPE_FUNC(char, u8, "'%c'")
>  
>  int PRINT_TYPE_FUNC_NAME(symbol)(struct trace_seq *s, void *data, void *ent)
>  {
> @@ -93,6 +94,7 @@ static const struct fetch_type probe_fetch_types[] = {
>  	ASSIGN_FETCH_TYPE_ALIAS(x16, u16, u16, 0),
>  	ASSIGN_FETCH_TYPE_ALIAS(x32, u32, u32, 0),
>  	ASSIGN_FETCH_TYPE_ALIAS(x64, u64, u64, 0),
> +	ASSIGN_FETCH_TYPE_ALIAS(char, u8, u8,  0),
>  	ASSIGN_FETCH_TYPE_ALIAS(symbol, ADDR_FETCH_TYPE, ADDR_FETCH_TYPE, 0),
>  
>  	ASSIGN_FETCH_TYPE_END
> diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> index de38f1c03776..8c86aaa8b0c9 100644
> --- a/kernel/trace/trace_probe.h
> +++ b/kernel/trace/trace_probe.h
> @@ -164,6 +164,7 @@ DECLARE_BASIC_PRINT_TYPE_FUNC(x16);
>  DECLARE_BASIC_PRINT_TYPE_FUNC(x32);
>  DECLARE_BASIC_PRINT_TYPE_FUNC(x64);
>  
> +DECLARE_BASIC_PRINT_TYPE_FUNC(char);
>  DECLARE_BASIC_PRINT_TYPE_FUNC(string);
>  DECLARE_BASIC_PRINT_TYPE_FUNC(symbol);
>  
> diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_char.tc b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_char.tc
> new file mode 100644
> index 000000000000..285b4770efad
> --- /dev/null
> +++ b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_char.tc
> @@ -0,0 +1,47 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0
> +# description: Kprobe event char type argument
> +# requires: kprobe_events
> +
> +case `uname -m` in
> +x86_64)
> +  ARG1=%di
> +;;
> +i[3456]86)
> +  ARG1=%ax
> +;;
> +aarch64)
> +  ARG1=%x0
> +;;
> +arm*)
> +  ARG1=%r0
> +;;
> +ppc64*)
> +  ARG1=%r3
> +;;
> +ppc*)
> +  ARG1=%r3
> +;;
> +s390*)
> +  ARG1=%r2
> +;;
> +mips*)
> +  ARG1=%r4
> +;;
> +*)
> +  echo "Please implement other architecture here"
> +  exit_untested
> +esac
> +
> +: "Test get argument (1)"
> +echo "p:testprobe tracefs_create_dir arg1=+0(${ARG1}):char" > kprobe_events
> +echo 1 > events/kprobes/testprobe/enable
> +echo "p:test $FUNCTION_FORK" >> kprobe_events
> +grep -qe "testprobe.* arg1='t'" trace
> +
> +echo 0 > events/kprobes/testprobe/enable
> +: "Test get argument (2)"
> +echo "p:testprobe tracefs_create_dir arg1=+0(${ARG1}):char arg2=+0(${ARG1}):char[4]" > kprobe_events
> +echo 1 > events/kprobes/testprobe/enable
> +echo "p:test $FUNCTION_FORK" >> kprobe_events
> +grep -qe "testprobe.* arg1='t' arg2={'t','e','s','t'}" trace