[PATCH v5 58/58] objtool/klp: Add test for ThinLTO symbols sharing a demangled name

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Three translation units linked with ThinLTO, two of which have a file-local
+ * helper of the same name.
+ *
+ * TU_C calls into both of the others, so ThinLTO imports entry_a and entry_b
+ * and with them the static helper each one calls.  A file-local symbol which
+ * has to become visible is renamed helper.llvm.<hash>, and the hash is content
+ * derived -- so the two helpers get different hashes from each other, and
+ * TU_A's gets a different one again after the patch changes it.  Only TU_A's
+ * changes: were both bodies to change, both would be cloned whichever way
+ * they were paired, and the pairing would not be observable.
+ *
+ * That leaves klp diff with two symbols in the original and two in the patched
+ * object, all four named differently, which have to be paired up correctly.
+ * Demangling alone gives "helper" for all of them; something else has to
+ * decide which is which.
+ *
+ * Only TU_A's helper changes.  That is what makes a wrong pairing observable:
+ * paired correctly, one helper is changed and the other is not, so exactly one
+ * is cloned.  Paired the wrong way round, both look changed -- or the wrong
+ * one does.  If both bodies changed the outcome would be the same either way
+ * and the test would prove nothing.
+ *
+ * BASE differs between the two so their bodies are not identical to begin
+ * with.
+ */
+
+#if defined(TU_C)
+extern int entry_a(int x);
+extern int entry_b(int x);
+int glue(int x) { return entry_a(x) + entry_b(x + 1); }
+#else
+#ifdef TU_B
+#define ENTRY entry_b
+#define BASE 5
+#else
+#define ENTRY entry_a
+#define BASE 10
+static const char __modinfo[]
+	__attribute__((section(".modinfo"), used, aligned(1))) = "\0name=vmlinux";
+#endif
+static __attribute__((noinline)) int helper(int x, int len)
+{
+	int sum = 0, i;
+
+	for (i = 0; i < len; i++)
+#if defined(PATCHED) && !defined(TU_B)
+		sum += i * 2 + BASE;	/* only TU_A's helper changes */
+#else
+		sum += i + BASE;
+#endif
+	return sum + x;
+}
+
+int ENTRY(int x) { return helper(x, 4); }
+#endif

@@ -0,0 +1,77 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Two ThinLTO-promoted symbols sharing a demangled name must be paired up
+# correctly.
+#
+# A file-local symbol which ThinLTO has to make visible is renamed
+# helper.llvm.<hash>.  With two such helpers in one link the original and the
+# patched object hold two each, all four spelled differently, and demangling
+# gives "helper" for all of them -- so the name is not enough to say which
+# corresponds to which.
+#
+# Getting it wrong is silent and specific: the patch is built against the wrong
+# body, so one call site gets the other helper's arithmetic.  Nothing fails to
+# build and nothing fails to load.
+#
+# test-thinlto-local covers the unambiguous case, one promoted symbol whose
+# hash moved.  This is the case where demangling alone is not an answer.
+#
+# The outcome is asserted, not the machinery: with the clang tested here the
+# pairing succeeds even with the .llvm.<hash> suffix map disabled and with
+# llvm_suffix() stubbed out, so no single-line sabotage distinguishes it.  The
+# tiered matcher this case was written for is not needed for this shape.
+#
+# Covers the same ground as corpus/x86_64-llvm-thinlto/
+# thin-lto-demangled-ambiguity and thin-lto-demangled-global-match in Joe
+# Lawrence's klp-build unit test corpus.
+
+. "$(dirname "$0")/../lib.sh"
+
+setup
+clang_only "ThinLTO requires clang"
+
+find_thinlto_toolchain ||
+	probe_skip "no matching clang/lld pair for a ThinLTO link; set THIN_LD to one"
+
+build_thinlto()		# $1 output object, $2 extra flags
+{
+	local t
+	for t in "" -DTU_B -DTU_C; do
+		$THIN_CC -flto=thin -O2 -ffunction-sections -fdata-sections \
+			$2 $t -c "$FIXTURES_DIR/thinlto_ambiguity.c" \
+			-o "$workdir/tu$t.o" 2>/dev/null || return 1
+	done
+	"$THIN_LD" -r "$workdir/tu.o" "$workdir/tu-DTU_B.o" "$workdir/tu-DTU_C.o" \
+		-o "$1" 2>/dev/null || return 1
+}
+
+build_thinlto "$workdir/orig.o" "" ||
+	probe_skip "ThinLTO build failed ($THIN_CC, $THIN_LD)"
+build_thinlto "$workdir/patched.o" -DPATCHED ||
+	probe_skip "ThinLTO build failed ($THIN_CC, $THIN_LD)"
+
+# The premise: two promoted helpers per object, and exactly one of them kept
+# its hash -- the one the patch did not touch.  Without that there is nothing
+# to disambiguate.
+orig_syms="$(in_symbols orig.o    | grep -oE 'helper\.llvm\.[0-9]+' | sort -u)"
+new_syms="$( in_symbols patched.o | grep -oE 'helper\.llvm\.[0-9]+' | sort -u)"
+[ "$(echo "$orig_syms" | wc -l)" = 2 ] && [ "$(echo "$new_syms" | wc -l)" = 2 ] ||
+	probe_skip "ThinLTO did not promote two distinct helpers here"
+
+kept="$(comm -12 <(echo "$orig_syms") <(echo "$new_syms"))"
+moved="$(comm -13 <(echo "$orig_syms") <(echo "$new_syms"))"
+[ "$(echo "$kept" | wc -w)" = 1 ] && [ "$(echo "$moved" | wc -w)" = 1 ] ||
+	probe_skip "expected one helper to keep its hash and one to move"
+
+run_diff
+
+# Exactly one helper is cloned, and it is the one whose body changed.  Cloning
+# the other, or both, is what a wrong pairing looks like.
+assert_not_patched "$kept"
+
+n="$(out_sections | grep -cE '[[:space:]]\.text\.helper\.llvm\.[0-9]+[[:space:]]')"
+[ "$n" = 1 ] ||
+	fail "expected 1 cloned helper, found $n"
+
+pass "ThinLTO helpers sharing a demangled name paired up correctly"