[PATCH v2 49/58] objtool/klp: Add test for tracepoint and pr_debug static branch keys

[Song Liu <song@kernel.org>]

A module-owned static branch key is normally fatal, because late module
patching lets the livepatch load before the module it depends on and
jump_label_add_module() then dereferences an unresolved entry.

Tracepoints and pr_debug() generate such keys everywhere, so refusing them
outright would make any function containing a trace_*() call or a
pr_debug() unpatchable.  klp diff drops the entry, warns, and carries on:
the patched code works with that one tracepoint or debug print permanently
off.

Both halves matter, and the test asserts both.  A build which fails is a
function nobody can patch; an entry left in place is the corruption the
rejection exists to prevent.

Give the fixture a KEY_NAME knob so the same static branch can be built
with either special name.  Verified by removing each exemption in turn --
the test fails for both.  That the entry is then dropped is asserted but
not isolated, and the test says so.

Assisted-by: Claude:claude-opus-4
Based-on-test-by: Joe Lawrence <joe.lawrence@redhat.com>
Assisted-by: Claude:claude-opus-5
Signed-off-by: Song Liu <song@kernel.org>
---
 .../generic/test-jump-label-exempt-keys.sh    | 51 +++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100755 tools/objtool/tests/generic/test-jump-label-exempt-keys.sh

diff --git a/tools/objtool/tests/generic/test-jump-label-exempt-keys.sh b/tools/objtool/tests/generic/test-jump-label-exempt-keys.sh
new file mode 100755
index 000000000000..fa2f913d860b
--- /dev/null
+++ b/tools/objtool/tests/generic/test-jump-label-exempt-keys.sh
@@ -0,0 +1,51 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Two kinds of module-owned static branch key are disabled with a warning
+# instead of rejected.
+#
+# A module-local key is normally fatal: late module patching lets the livepatch
+# load before the module it depends on, so the unresolved __jump_table entry is
+# dereferenced by jump_label_add_module().  test-jump-label-module-key covers
+# that rejection.
+#
+# Tracepoints and pr_debug() generate such keys everywhere, though, and
+# refusing them outright would make any function containing a trace_*() call or
+# a pr_debug() unpatchable.  So klp diff drops the entry, says so, and carries
+# on: the patched code keeps working with that one tracepoint or debug print
+# permanently off.
+#
+# Both halves matter.  A build that fails is a function nobody can patch; an
+# entry left in place is the memory corruption the rejection exists to prevent.
+#
+# The two exemptions are isolated: remove either and this fails.  That the
+# entry is then dropped is asserted but not isolated -- making the caller keep
+# it anyway produces no output difference here, so that assertion stands as a
+# check on the behaviour rather than on the line which produces it.
+#
+# Covers the same ground as corpus/x86_64/static-call-module-tracepoint and
+# pr-debug-unsupported in Joe Lawrence's klp-build unit test corpus.
+
+. "$(dirname "$0")/../lib.sh"
+
+setup
+
+# check <key name> <expected warning>
+check()
+{
+	build_pair jump_label.c -DKEY_NAME="$1" -DMODNAME='"klp_testmod"'
+	require_input_section __jump_table
+
+	# Accepted, not rejected: this is the whole point.
+	run_diff
+	assert_diff_log "$2"
+
+	# And the entry is gone, not merely complained about.
+	assert_patched target
+	assert_no_section __jump_table
+}
+
+check __tracepoint_klp_test        'disabling unsupported tracepoint klp_test'
+check __UNIQUE_ID_ddebug_klp_test  'disabling unsupported pr_debug'
+
+pass "tracepoint and pr_debug keys disabled with a warning, not rejected"
-- 
2.53.0-Meta