[PATCH v2 6/9] tests: Add inter-CU type reference comparison test

[Arnaldo Carvalho de Melo <acme@kernel.org>]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

When the perf binary includes Rust CUs, some DWARF types reference types
in other CUs via DW_FORM_ref_addr. The parallel loading path processes
each CU independently, so cross-CU references fail during
cu__recode_dwarf_types() and the types become unresolved (void).

The force_cu_merging feature worked around this by serializing loading
into a mega-CU, but disables parallel DIE processing. This test
compares both outputs to validate that cross-CU references are
correctly resolved without needing force_cu_merging.

Before the cus__merging_cu() fix earlier in this series, 314 cross-CU
references failed, producing 70
lines of output difference across 12 diff hunks:

  $ pahole -F dwarf ~/bin/perf 2>/dev/null > parallel.txt
  $ pahole --features=force_cu_merging -F dwarf ~/bin/perf 2>/dev/null > merged.txt
  $ diff parallel.txt merged.txt | grep '^[<>]' | wc -l
  70
  $ diff -u parallel.txt merged.txt | head -20
  --- parallel.txt
  +++ merged.txt
  @@ -10821,7 +10821,11 @@
   	usize                      __0 __attribute__((__aligned__(8)));
   	struct ThreadInfo          __1 __attribute__((__aligned__(8)));

  +	/* XXX last struct has 8 bytes of padding, 1 hole */
  +
   	/* size: 48, cachelines: 1, members: 2 */
  +	/* member types with holes: 1, total: 1 */
  +	/* paddings: 1, sum paddings: 8 */
   	/* forced alignments: 2 */
   	/* last cacheline: 48 bytes */
   } __attribute__((__aligned__(8)));

An earlier commit in this series fixed the detection of DW_FORM_ref_addr
in cus__merging_cu(), making this test pass.

Assisted-by: Claude:claude-sonnet-4-5
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tests/inter_cu_refs.sh | 50 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100755 tests/inter_cu_refs.sh

diff --git a/tests/inter_cu_refs.sh b/tests/inter_cu_refs.sh
new file mode 100755
index 0000000000000000..0df0ce13cd948f1f
--- /dev/null
+++ b/tests/inter_cu_refs.sh
@@ -0,0 +1,50 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+# Copyright © 2026 Red Hat Inc, Arnaldo Carvalho de Melo <acme@redhat.com>
+#
+# Compare default CU loading with explicit force_cu_merging for binaries
+# with inter-CU type references (e.g. Rust CUs in perf).
+#
+# When cus__merging_cu() correctly detects DW_FORM_ref_addr usage, it
+# automatically falls back to the merged CU path.  This test verifies
+# that the automatic detection produces the same output as explicitly
+# forcing CU merging.
+
+. "$(dirname "$0")/test_lib.sh"
+
+outdir=$(make_tmpdir)
+trap cleanup EXIT
+
+title_log "Compare parallel vs merged CU loading for inter-CU type references."
+
+perf=$(which perf 2>/dev/null)
+if [ -z "$perf" ] ; then
+	info_log "skip: No 'perf' binary available"
+	test_skip
+fi
+
+if ! pahole --features=force_cu_merging -F dwarf -C perf_event_header "$perf" 2>/dev/null | grep -q "^struct perf_event_header {" ; then
+	info_log "skip: $perf doesn't have 'struct perf_event_header' type info"
+	test_skip
+fi
+
+parallel_out=$outdir/parallel.txt
+merged_out=$outdir/merged.txt
+
+if ! pahole -F dwarf "$perf" > "$parallel_out" 2>/dev/null ; then
+	error_log "FAIL: pahole failed processing $perf (parallel mode)"
+	test_fail
+fi
+
+if ! pahole --features=force_cu_merging -F dwarf "$perf" > "$merged_out" 2>/dev/null ; then
+	error_log "FAIL: pahole failed processing $perf (merged mode)"
+	test_fail
+fi
+
+if diff -u "$parallel_out" "$merged_out" > /dev/null 2>&1 ; then
+	test_pass
+else
+	nr_diff=$(diff "$parallel_out" "$merged_out" | grep '^[<>]' | wc -l)
+	error_log "FAIL: $nr_diff lines differ between parallel and merged CU loading"
+	test_fail
+fi
-- 
2.55.0