linux-kernel - Re: [PATCH v2 1/2] selftests: livepatch: add new ftrace helpers functions

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Message-ID: <Z+Gi/QEFPffEonTE@redhat.com>
Date: Mon, 24 Mar 2025 14:22:53 -0400
From: Joe Lawrence <joe.lawrence@...hat.com>
To: Filipe Xavier <felipeaggger@...il.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, Jiri Kosina <jikos@...nel.org>,
	Miroslav Benes <mbenes@...e.cz>, Petr Mladek <pmladek@...e.com>,
	Shuah Khan <shuah@...nel.org>,
	Marcos Paulo de Souza <mpdesouza@...e.com>,
	live-patching@...r.kernel.org, linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org, felipe_life@...e.com
Subject: Re: [PATCH v2 1/2] selftests: livepatch: add new ftrace helpers
 functions

On Tue, Mar 18, 2025 at 06:20:35PM -0300, Filipe Xavier wrote:
> Add new ftrace helpers functions cleanup_tracing, trace_function and
> check_traced_functions.
> 
> Signed-off-by: Filipe Xavier <felipeaggger@...il.com>
> ---
>  tools/testing/selftests/livepatch/functions.sh | 49 ++++++++++++++++++++++++++
>  1 file changed, 49 insertions(+)
> 
> diff --git a/tools/testing/selftests/livepatch/functions.sh b/tools/testing/selftests/livepatch/functions.sh
> index 15601402dee6567837c2c49ba342eb357e410d18..dea9cc10a3f09662c57c2593cff49423302c8a5c 100644
> --- a/tools/testing/selftests/livepatch/functions.sh
> +++ b/tools/testing/selftests/livepatch/functions.sh
> @@ -10,6 +10,7 @@ SYSFS_KERNEL_DIR="/sys/kernel"
>  SYSFS_KLP_DIR="$SYSFS_KERNEL_DIR/livepatch"
>  SYSFS_DEBUG_DIR="$SYSFS_KERNEL_DIR/debug"
>  SYSFS_KPROBES_DIR="$SYSFS_DEBUG_DIR/kprobes"
> +SYSFS_TRACING_DIR="$SYSFS_DEBUG_DIR/tracing"
>  
>  # Kselftest framework requirement - SKIP code is 4
>  ksft_skip=4
> @@ -62,6 +63,9 @@ function push_config() {
>  			awk -F'[: ]' '{print "file " $1 " line " $2 " " $4}')
>  	FTRACE_ENABLED=$(sysctl --values kernel.ftrace_enabled)
>  	KPROBE_ENABLED=$(cat "$SYSFS_KPROBES_DIR/enabled")
> +	TRACING_ON=$(cat "$SYSFS_TRACING_DIR/tracing_on")
> +	CURRENT_TRACER=$(cat "$SYSFS_TRACING_DIR/current_tracer")
> +	FTRACE_FILTER=$(cat "$SYSFS_TRACING_DIR/set_ftrace_filter")
>  }
>  
>  function pop_config() {
> @@ -74,6 +78,17 @@ function pop_config() {
>  	if [[ -n "$KPROBE_ENABLED" ]]; then
>  		echo "$KPROBE_ENABLED" > "$SYSFS_KPROBES_DIR/enabled"
>  	fi
> +	if [[ -n "$TRACING_ON" ]]; then
> +		echo "$TRACING_ON" > "$SYSFS_TRACING_DIR/tracing_on"
> +	fi
> +	if [[ -n "$CURRENT_TRACER" ]]; then
> +		echo "$CURRENT_TRACER" > "$SYSFS_TRACING_DIR/current_tracer"
> +	fi
> +	if [[ -n "$FTRACE_FILTER" ]]; then
> +		echo "$FTRACE_FILTER" \
> +			| sed -e "/#### all functions enabled ####/d"
> +			> "$SYSFS_TRACING_DIR/set_ftrace_filter"
> +	fi
>  }
>  
>  function set_dynamic_debug() {
> @@ -352,3 +367,37 @@ function check_sysfs_value() {
>  		die "Unexpected value in $path: $expected_value vs. $value"
>  	fi
>  }
> +
> +# cleanup_tracing() - stop and clean up function tracing
> +function cleanup_tracing() {
> +	echo 0 > "$SYSFS_TRACING_DIR/tracing_on"
> +	echo "" > "$SYSFS_TRACING_DIR/set_ftrace_filter"
> +	echo "nop" > "$SYSFS_TRACING_DIR/current_tracer"
> +	echo "" > "$SYSFS_TRACING_DIR/trace"
> +}
> +
> +# trace_function(function) - start tracing of a function
> +#	function - to be traced function
> +function trace_function() {
> +	local function="$1"; shift
> +
> +	cleanup_tracing
> +
> +	echo "function" > "$SYSFS_TRACING_DIR/current_tracer"
> +	echo "$function" > "$SYSFS_TRACING_DIR/set_ftrace_filter"
> +	echo 1 > "$SYSFS_TRACING_DIR/tracing_on"
> +}
> +
> +# check_traced_functions(functions...) - check whether each function appeared in the trace log
> +#	functions - list of functions to be checked
> +function check_traced_functions() {
> +	local function
> +
> +	for function in "$@"; do
> +		if ! grep -q "$function" "$SYSFS_TRACING_DIR/trace" ; then

Small suggestion here: grep on "$function" may find partial string
matches, like:

  $ echo 'hamburger' | grep 'ham'
  hamburger

so it's probably safer to user --word-regexp to avoid longer function
names inadvertently matching:

  $ echo 'hamburger' | grep -w 'ham'
  $ echo 'ham' | grep -w 'ham'
  ham

Also, maybe also --fixed-strings for the extra paranoid?  Off the top of
my head, I don't think any C function characters are special regex (like
$ ^ [ ] etc.) so it's probably safe w/o.

-- Joe