perf test: Add file offset diagnostic test for corrupted perf.data

Add a shell test that verifies the file_offset diagnostic messages
work correctly when perf encounters corrupted events.

The test corrupts a MMAP2 event's size field in a recorded perf.data
file, then checks that perf report produces warning messages that
include both the file offset (e.g. "at offset 0x2738:") and the
event type name with numeric id (e.g. "MMAP2 (10)").

This exercises the diagnostic improvements from the file_offset
series, which retrofitted all skip/stop/error messages to include
the position and type of the problematic event.

Reviewed-by: Ian Rogers <irogers@google.com>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/shell/data_file_offset_diagnostics.sh

@@ -0,0 +1,91 @@
+#!/bin/bash
+# Test that perf report includes file offsets and event type names in diagnostic messages.
+# SPDX-License-Identifier: GPL-2.0
+#
+# The file_offset diagnostic series adds "at offset 0x...: TYPE (N)"
+# to all skip/stop/error messages.  This test corrupts an event's size
+# field in a perf.data file, then verifies the resulting warning
+# includes the file offset and event type.
+
+err=0
+
+cleanup() {
+	[ -n "${perfdata}" ] && rm -f "${perfdata}" "${perfdata}.old"
+	rm -f "${corrupted}" "${stderrfile}"
+	trap - EXIT TERM INT
+}
+trap 'cleanup; exit 1' TERM INT
+trap cleanup EXIT
+
+perfdata=$(mktemp /tmp/__perf_test.perf.data.XXXXX) || exit 2
+corrupted=$(mktemp /tmp/__perf_test.perf.data.XXXXX) || exit 2
+stderrfile=$(mktemp /tmp/__perf_test.perf.data.XXXXX) || exit 2
+
+if ! perf record -o "${perfdata}" -- perf test -w noploop 2>/dev/null; then
+	echo "Skip: perf record failed"
+	cleanup
+	exit 2
+fi
+
+# Find the file offset of the first MMAP2 event via perf report -D.
+# Format: "timestamp 0xOFFSET [0xSIZE]: PERF_RECORD_MMAP2 ..."
+mmap2_line=$(perf report -D -i "${perfdata}" 2>/dev/null | grep "PERF_RECORD_MMAP2" | head -1)
+if [ -z "${mmap2_line}" ]; then
+	echo "Skip: no MMAP2 events found in perf.data"
+	cleanup
+	exit 2
+fi
+
+mmap2_offset=$(echo "${mmap2_line}" | awk '{print $2}')
+mmap2_offset_dec=$((mmap2_offset))
+
+# Copy the file and corrupt the MMAP2 event's size field.
+# perf_event_header layout: type(u32) misc(u16) size(u16)
+# Set size to 16 — below the MMAP2 minimum, which triggers
+# the "event size too small" warning.
+#
+# perf.data uses native byte order, so write the u16 in the
+# host's endianness to work on both LE and BE architectures.
+cp "${perfdata}" "${corrupted}"
+if printf '\x01\x02' | od -A n -t x2 | grep -q "0201"; then
+	# Little-endian
+	printf '\x10\x00'
+else
+	# Big-endian
+	printf '\x00\x10'
+fi | dd of="${corrupted}" bs=1 seek=$((mmap2_offset_dec + 6)) conv=notrunc 2>/dev/null
+
+perf report -i "${corrupted}" --stdio > /dev/null 2> "${stderrfile}"
+
+# Check that warnings include "at offset 0x..."
+if grep -q "at offset 0x" "${stderrfile}"; then
+	echo "File offset in diagnostics [Success]"
+else
+	echo "File offset in diagnostics [Failed: no 'at offset 0x...' found]"
+	echo "  stderr was:"
+	head -5 "${stderrfile}"
+	err=1
+fi
+
+# Check that the event type name and numeric id appear: "MMAP2 (10)"
+if grep -q "MMAP2 (10)" "${stderrfile}"; then
+	echo "Event type name in diagnostics [Success]"
+else
+	echo "Event type name in diagnostics [Failed: no 'MMAP2 (10)' found]"
+	echo "  stderr was:"
+	head -5 "${stderrfile}"
+	err=1
+fi
+
+# Check that the reported offset matches the actual corruption point
+if grep -q "at offset ${mmap2_offset}:" "${stderrfile}"; then
+	echo "Correct offset reported [Success]"
+else
+	echo "Correct offset reported [Failed: expected offset ${mmap2_offset}]"
+	echo "  stderr was:"
+	head -5 "${stderrfile}"
+	err=1
+fi
+
+cleanup
+exit ${err}