Re: [PATCH v2] perf test: Fix inet_pton probe failure and unroll call graph

[Thomas Richter <tmricht@linux.ibm.com>]

On 4/11/26 21:37, Ian Rogers wrote:
> When adding a probe for libc's inet_pton, perf probe may create multiple
> probe points (e.g., due to inlining or multiple symbol resolutions),
> resulting in multiple identical event names being output (e.g.,
> `probe_libc:inet_pton_1`).
> 
> The script previously used a brittle pipeline (`tail -n +2 | head -n -5`)
> and an awk script to extract the event name. When multiple probes were
> added, awk would output the event name multiple times, which expanded
> to multiple words in bash. This broke the subsequent `perf record` and
> `perf probe -d` commands, causing the test to fail with:
> `Error: another command except --add is set.`
> 
> Fix this by removing the brittle `tail/head` commands and appending
> `| head -n 1` to the awk extraction. This ensures that only a single,
> unique event name is captured, regardless of how many probe points
> are created.
> 
> Additionally, the test artificially limited the backtrace size via
> `max-stack=4` and did not specify dwarf call graphs for non-s390x
> architectures. In newer libc versions where `inet_pton` is nested
> deeper or compiled without frame pointers, `perf script` failed to resolve
> the backtrace up to `/bin/ping`. Fix this by explicitly collecting
> dwarf call-graphs for all architectures and increasing `max-stack` to 8.
> 
> Assisted-by: Gemini:gemini-3.1-pro-preview
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/perf/tests/shell/record+probe_libc_inet_pton.sh | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/tests/shell/record+probe_libc_inet_pton.sh b/tools/perf/tests/shell/record+probe_libc_inet_pton.sh
> index ab99bef556bf..eca629ee83f0 100755
> --- a/tools/perf/tests/shell/record+probe_libc_inet_pton.sh
> +++ b/tools/perf/tests/shell/record+probe_libc_inet_pton.sh
> @@ -22,9 +22,9 @@ event_pattern='probe_libc:inet_pton(_[[:digit:]]+)?'
>  
>  add_libc_inet_pton_event() {
>  
> -	event_name=$(perf probe -f -x $libc -a inet_pton 2>&1 | tail -n +2 | head -n -5 | \
> +	event_name=$(perf probe -f -x $libc -a inet_pton 2>&1 | \
>  			awk -v ep="$event_pattern" -v l="$libc" '$0 ~ ep && $0 ~ \
> -			("\\(on inet_pton in " l "\\)") {print $1}')
> +			("\\(on inet_pton in " l "\\)") {print $1}' | head -n 1)
>  
>  	if [ $? -ne 0 ] || [ -z "$event_name" ] ; then
>  		printf "FAIL: could not add event\n"
> @@ -40,12 +40,12 @@ trace_libc_inet_pton_backtrace() {
>  	echo ".*inet_pton\+0x[[:xdigit:]]+[[:space:]]\($libc|inlined\)$" >> $expected
>  	case "$(uname -m)" in
>  	s390x)
> -		eventattr='call-graph=dwarf,max-stack=4'
> +		eventattr='call-graph=dwarf,max-stack=8'
>  		echo "((__GI_)?getaddrinfo|text_to_binary_address)\+0x[[:xdigit:]]+[[:space:]]\($libc|inlined\)$" >> $expected
>  		echo "(gaih_inet|main)\+0x[[:xdigit:]]+[[:space:]]\(inlined|.*/bin/ping.*\)$" >> $expected
>  		;;
>  	*)
> -		eventattr='max-stack=4'
> +		eventattr='call-graph=dwarf,max-stack=8'
>  		echo ".*(\+0x[[:xdigit:]]+|\[unknown\])[[:space:]]\(.*/bin/ping.*\)$" >> $expected
>  		;;
>  	esac

for s390:

Tested-by: Thomas Richter <tmricht@linux.ibm.com>

-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH

Vorsitzender des Aufsichtsrats: Wolfgang Wendt

Geschäftsführung: David Faller

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