[tip: objtool/core] objtool/klp: Add test for a static branch introduced by the patch

[tip-bot2 for Song Liu]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     548b6ec15cfcf190cf1231d20c2473f4f22a810c
Gitweb:        https://git.kernel.org/tip/548b6ec15cfcf190cf1231d20c2473f4f22a810c
Author:        Song Liu <song@xxxxxxxxxx>
AuthorDate:    Wed, 16 Sep 2026 11:43:41 -07:00
Committer:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Wed, 16 Sep 2026 17:21:46 -07:00

objtool/klp: Add test for a static branch introduced by the patch

Patching a function which already has a static branch and adding one to a
function which had none are different cases.  In the second the
__jump_table entry is itself new, so there is nothing in the original to
correlate it against: klp diff has to carry the entry into the patch from
scratch and reach the key the way it reaches any other vmlinux symbol.

Dropping it is silent.  The patched function keeps a static branch the
kernel never patches, so it takes the same arm forever whatever the key is
set to.

Give the fixture a NEW_KEY knob which puts the whole branch behind PATCHED,
and assert the premise -- that the original really has no __jump_table --
before asserting the result, since otherwise this is just a second copy of
test-jump-label-key.

Verified by making klp diff skip __jump_table when cloning special
sections: the test fails.

Assisted-by: Claude:claude-opus-4
Based-on-test-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-5
Signed-off-by: Song Liu <song@xxxxxxxxxx>
Link: https://patch.msgid.link/20260916184351.2720310-49-song@xxxxxxxxxx
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 tools/objtool/tests/generic/test-jump-label-new-key.sh | 51 +++++++++-
 1 file changed, 51 insertions(+)
 create mode 100755 tools/objtool/tests/generic/test-jump-label-new-key.sh

diff --git a/tools/objtool/tests/generic/test-jump-label-new-key.sh b/tools/objtool/tests/generic/test-jump-label-new-key.sh
new file mode 100755
index 0000000..3bc6005
--- /dev/null
+++ b/tools/objtool/tests/generic/test-jump-label-new-key.sh
@@ -0,0 +1,51 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# A patch may introduce a static branch where the original function had none.
+#
+# That is not the same case as patching a function which already has one.  The
+# __jump_table entry is itself new, so there is no counterpart in the original
+# to correlate it against: klp diff has to carry the entry and the key into the
+# patch from scratch, and the key has to be reached the way any other reference
+# to a vmlinux symbol is.
+#
+# Get it wrong and the entry is dropped, leaving a static branch the kernel
+# never patches -- the code takes the wrong arm forever, silently.
+#
+# Where the key lives still decides whether that is allowed, exactly as it does
+# for a key the original already had: a module-owned one cannot be reached, so
+# introducing one has to stop the build rather than emit an entry nothing will
+# resolve.
+#
+# Covers the same ground as corpus/x86_64/static-branch-vmlinux-new and
+# static-branch-module-new in Joe Lawrence's klp-build unit test corpus.
+
+. "$(dirname "$0")/../lib.sh"
+
+setup klp_test_key
+build_pair jump_label.c -DNEW_KEY
+
+# The premise: the original really has no jump table, and the patched one does.
+has_input_section orig.o __jump_table &&
+	fail "fixture put a __jump_table in the original; nothing new to add"
+has_input_section patched.o __jump_table ||
+	probe_skip "compiler produced no __jump_table on this arch"
+
+run_diff
+
+assert_patched target
+assert_section __jump_table
+assert_reloc_sym __jump_table target
+
+# The same new branch, with the key owned by a module.  Drop the vmlinux export
+# first: while it is exported the key is reachable and being new changes
+# nothing, which is what the first version of this got wrong.
+export_syms
+rm -f "$workdir/out.o"
+build_pair jump_label.c -DNEW_KEY -DMODNAME='"klp_testmod"'
+run_diff 255
+assert_diff_log 'unsupported static branch key klp_test_key'
+[ -e "$workdir/out.o" ] &&
+	fail "output object produced for a rejected input"
+
+pass "static branch introduced by the patch carried in, or rejected for a module key"