[PATCH v2 16/58] objtool/klp: Add test for cold function halves

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Function the compiler may split into a hot part and a foo.cold part. */
+
+static const char __modinfo[]
+	__attribute__((section(".modinfo"), used, aligned(1))) = "\0name=vmlinux";
+
+static void __attribute__((cold, noinline)) slow_path(int x)
+{
+	__asm__ volatile("" :: "r"(x));
+}
+
+int target(int x)
+{
+	if (__builtin_expect(x < 0, 0))
+		slow_path(x);
+#ifdef PATCHED
+	return x + 2;
+#else
+	return x + 1;
+#endif
+}

@@ -0,0 +1,34 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Both halves of a split function belong to the patch; carrying only the hot
+# part leaves the cold path branching into unpatched code.
+
+. "$(dirname "$0")/../lib.sh"
+
+# Clang does not split functions into a cold part at all, so there is nothing
+# for this test to look at there.  A given gcc may or may not split, which is a
+# version property rather than a compiler choice -- that stays a probe below.
+gcc_only "clang does not split functions into a cold part"
+
+setup
+
+split_flag=-freorder-blocks-and-partition
+cc_supports "$split_flag" || split_flag=
+
+build_pair cold_function.c $split_flag
+
+in_symbols orig.o | grep -qE 'target\.cold' ||
+	probe_skip "compiler did not split the function into a cold part"
+
+run_diff
+
+assert_patched target
+# Not a bare name match: had the cold half been left behind, the branch to
+# it would appear as an undefined .klp.sym.vmlinux.target.cold, whose name
+# contains the one being looked for.  Require a defined symbol.
+out_symbols | awk '$7 != "UND" && $8 ~ /target\.cold/ { found = 1 }
+	END { exit !found }' ||
+	fail "cold half was not carried into the patch"
+
+pass "cold half carried into the patch with its parent"