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Date: Tue, 24 Jan 2023 17:38:00 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Donglin Peng <dolinux.peng@...il.com>
Cc: mhiramat@...nel.org, xiehuan09@...il.com,
linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v6] tracing/probe: add a char type to show the character
value of traced arguments
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@...il.com> 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@...il.com>
> Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> Reported-by: kernel test robot <lkp@...el.com>
> ---
> 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
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