[PATCH v4 27/58] objtool/klp: Add klp diff and post-link regression tests

[Song Liu <song@kernel.org>]

Five tests covering behaviour the harness could reach but nothing
exercised.  Each was verified to fail against the code it guards, by
reverting the fix or sabotaging the exact line; where a first attempt
passed against broken code, the fixture was wrong and was rebuilt.

  post-link                    first coverage of the subcommand at all
  local-vs-export              local symbols must not match exports
  symvers-parse-error          Module.symvers parse error line numbers
  checksum-debug               the --debug-checksum format klp-build reads
  function-removal             the "no correlation" path

local-vs-export tests the behavior of commit 86a697572c62 ("objtool/klp:
Don't match local symbols against exports"), and symvers-parse-error that
of commit 51c1de134863 ("objtool/klp: Fix line numbers in Module.symvers
parse errors").

Assisted-by: Claude:claude-opus-5
Signed-off-by: Song Liu <song@kernel.org>
---
 .../tests/generic/fixtures/function_removal.c | 25 ++++++++++
 .../tests/generic/test-checksum-debug.sh      | 49 +++++++++++++++++++
 .../tests/generic/test-function-removal.sh    | 34 +++++++++++++
 .../tests/generic/test-local-vs-export.sh     | 32 ++++++++++++
 tools/objtool/tests/generic/test-post-link.sh | 42 ++++++++++++++++
 .../tests/generic/test-symvers-parse-error.sh | 23 +++++++++
 6 files changed, 205 insertions(+)
 create mode 100644 tools/objtool/tests/generic/fixtures/function_removal.c
 create mode 100755 tools/objtool/tests/generic/test-checksum-debug.sh
 create mode 100755 tools/objtool/tests/generic/test-function-removal.sh
 create mode 100755 tools/objtool/tests/generic/test-local-vs-export.sh
 create mode 100755 tools/objtool/tests/generic/test-post-link.sh
 create mode 100755 tools/objtool/tests/generic/test-symvers-parse-error.sh

diff --git a/tools/objtool/tests/generic/fixtures/function_removal.c b/tools/objtool/tests/generic/fixtures/function_removal.c
new file mode 100644
index 000000000000..d65ff604c2c5
--- /dev/null
+++ b/tools/objtool/tests/generic/fixtures/function_removal.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * A function the patch deletes, along with its only caller's use of it.  The
+ * original has a symbol which the patched object simply does not, so there is
+ * nothing to correlate it against.
+ */
+
+static const char __modinfo[]
+	__attribute__((section(".modinfo"), used, aligned(1))) = "\0name=vmlinux";
+
+#ifndef PATCHED
+int going_away(int x)
+{
+	return x + 7;
+}
+#endif
+
+int caller(int x)
+{
+#ifdef PATCHED
+	return x + 1;
+#else
+	return going_away(x);
+#endif
+}
diff --git a/tools/objtool/tests/generic/test-checksum-debug.sh b/tools/objtool/tests/generic/test-checksum-debug.sh
new file mode 100755
index 000000000000..78856b191636
--- /dev/null
+++ b/tools/objtool/tests/generic/test-checksum-debug.sh
@@ -0,0 +1,49 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# "klp checksum --debug-checksum" prints a per-instruction checksum stream,
+# and klp-build -f (--show-first-changed) parses it to report where a function
+# first differs between the original and patched builds.
+#
+# It is a debugging aid, so nothing fails when it breaks: klp-build greps the
+# stream, and an unmatched grep just yields no output, which reads as "no
+# instruction changed".  That is exactly how the format drifted out from under
+# it once already.  Pin the shape klp-build depends on:
+#
+#   DEBUG: <object>: checksum: <func>(): <sym>+0x<offset> <16 hex digits>
+#
+# and that --dry-run leaves the object alone, since klp-build runs this against
+# objects it is going to checksum again for real.
+
+. "$(dirname "$0")/../lib.sh"
+
+setup
+build_pair basic.c
+
+before="$(md5sum < "$workdir/orig.o")"
+
+"$OBJTOOL" klp checksum --dry-run --debug-checksum=changed \
+	"$workdir/orig.o" > "$workdir/debug.log" 2>&1 ||
+	fail "klp checksum --debug-checksum failed"
+
+# --dry-run has to mean it: klp-build checksums these objects again afterwards,
+# and "already has .discard.sym_checksum, skipping" would lose the real run.
+[ "$(md5sum < "$workdir/orig.o")" = "$before" ] ||
+	fail "--dry-run modified the object"
+has_input_section orig.o .discard.sym_checksum &&
+	fail "--dry-run created .discard.sym_checksum"
+
+grep -qE '^DEBUG: .*: checksum: changed\(\): [^ ]+\+0x[0-9a-f]+ [0-9a-f]{16}$' \
+	"$workdir/debug.log" ||
+	fail "unexpected --debug-checksum format: $(head -1 "$workdir/debug.log")"
+
+# This is the pattern klp-build greps with.  Keep it working verbatim.
+grep -qE "^DEBUG: .*checksum: changed\(\): " "$workdir/debug.log" ||
+	fail "klp-build's --show-first-changed pattern no longer matches"
+
+# Only the requested function, or klp-build attributes instructions to the
+# wrong one.
+grep -qE 'checksum: untouched\(\)' "$workdir/debug.log" &&
+	fail "--debug-checksum=changed also dumped untouched()"
+
+pass "--debug-checksum format is the one klp-build -f parses"
diff --git a/tools/objtool/tests/generic/test-function-removal.sh b/tools/objtool/tests/generic/test-function-removal.sh
new file mode 100755
index 000000000000..df76e81e3936
--- /dev/null
+++ b/tools/objtool/tests/generic/test-function-removal.sh
@@ -0,0 +1,34 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# A patch which deletes a function leaves a symbol in the original with no
+# counterpart in the patched object.  klp diff cannot correlate it, and must
+# say so and carry on: livepatching cannot remove code from a running kernel,
+# so what matters is that the surviving caller is patched and the deleted
+# function is not dragged into the patch module.
+#
+# Cloning it would be worse than useless -- dead code in the patch, plus
+# whatever it references, resolved against a kernel where it may not exist.
+
+. "$(dirname "$0")/../lib.sh"
+
+setup
+build_pair function_removal.c
+
+# One-sided by construction: present in the original, gone from the patched.
+has_input_symbol orig.o going_away ||
+	fail "fixture has no going_away in the original"
+has_input_symbol patched.o going_away &&
+	fail "fixture still has going_away in the patched object"
+
+run_diff
+
+assert_diff_log 'no correlation: going_away'
+
+# The caller changed, so it is patched ...
+assert_patched caller
+# ... and the deleted function comes along in no form at all.
+assert_not_patched going_away
+assert_no_symbol going_away
+
+pass "deleted function reported as uncorrelated and left out of the patch"
diff --git a/tools/objtool/tests/generic/test-local-vs-export.sh b/tools/objtool/tests/generic/test-local-vs-export.sh
new file mode 100755
index 000000000000..5b91101dadd6
--- /dev/null
+++ b/tools/objtool/tests/generic/test-local-vs-export.sh
@@ -0,0 +1,32 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# find_export() matched on symbol name alone, so a static function or variable
+# sharing a name with an export was mistaken for a reference to that export.
+# For a vmlinux export that means no klp relocation at all: the normal
+# relocation left behind is resolved by the module loader to the vmlinux
+# symbol, and the patched code quietly reads and writes the wrong object.
+#
+# Exports are always global, so a local symbol is never one.
+
+. "$(dirname "$0")/../lib.sh"
+
+setup
+build_pair static_local.c
+
+# The static the fixture uses.  Compilers mangle statics variously -- gcc says
+# counter.0, clang says target.counter -- so find what this one produced rather
+# than assuming a shape.
+local_sym="$(in_symbols orig.o |
+	awk '$4 == "OBJECT" && $5 == "LOCAL" && $8 ~ /counter/ { print $8; exit }')"
+[ -n "$local_sym" ] ||
+	fail "fixture produced no local 'counter' symbol"
+
+# Contrive the collision: something else exports that same name.
+export_syms "$local_sym" counter
+run_diff
+
+# Still treated as the local it is, not as the export.
+assert_klp_sym "$local_sym" vmlinux
+
+pass "local symbol not mistaken for an export of the same name"
diff --git a/tools/objtool/tests/generic/test-post-link.sh b/tools/objtool/tests/generic/test-post-link.sh
new file mode 100755
index 000000000000..a6d40ae1b18d
--- /dev/null
+++ b/tools/objtool/tests/generic/test-post-link.sh
@@ -0,0 +1,42 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# klp post-link converts the intermediate __klp_relocs.* sections into the
+# .klp.rela.* form the kernel applies at patch load.  Getting this wrong is
+# invisible at build time: the module links and loads, and the relocations are
+# simply never applied.
+
+. "$(dirname "$0")/../lib.sh"
+
+setup
+build_pair static_local.c
+
+# An unexported symbol is what produces a klp relocation in the first place.
+# The static local is renamed by the compiler -- counter.0 with gcc -- so the
+# fixture's premise is that some local of that shape exists, not that a symbol
+# called "counter" does.  Find it first; everything below names it.
+local_sym="$(in_symbols orig.o |
+	     awk '$4 == "OBJECT" && $5 == "LOCAL" && $8 ~ /counter/ { print $8; exit }')"
+[ -n "$local_sym" ] || fail "fixture produced no local 'counter' symbol"
+
+run_diff
+assert_section __klp_relocs.vmlinux
+
+# Nothing has converted them yet.
+assert_no_section ".klp.rela.vmlinux..text.target"
+
+# The original relocation is neutralised by pointing it at a tombstone, which
+# is what stops the module loader resolving it behind livepatch's back.
+#
+# Compilers mangle a static local differently -- gcc says counter.0, clang
+# target.counter -- so find what this one produced rather than assuming.
+assert_tombstone "$local_sym"
+
+run_post_link
+
+# One .klp.rela section per base section, carrying SHF_RELA_LIVEPATCH, against
+# a symbol in SHN_LIVEPATCH for the kernel to resolve.
+assert_klp_rela vmlinux .text.target
+assert_livepatch_sym "$local_sym"
+
+pass "klp relocations converted to .klp.rela with SHN_LIVEPATCH symbols"
diff --git a/tools/objtool/tests/generic/test-symvers-parse-error.sh b/tools/objtool/tests/generic/test-symvers-parse-error.sh
new file mode 100755
index 000000000000..d597f28e5617
--- /dev/null
+++ b/tools/objtool/tests/generic/test-symvers-parse-error.sh
@@ -0,0 +1,23 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# A malformed Module.symvers has to be reported against the line it is on.
+# Module.symvers has tens of thousands of lines and is generated, so a wrong
+# line number sends whoever has to fix it to the wrong place, and "line 1" is
+# wrong in a way that looks plausible.
+
+. "$(dirname "$0")/../lib.sh"
+
+setup
+build_pair basic.c
+
+# Three well-formed lines, then one with no tabs at all.
+export_syms a b c
+echo 'this line has no fields' >> "$workdir/Module.symvers"
+
+run_diff 255
+
+assert_diff_log 'malformed Module.symvers'
+assert_diff_log 'at line 4'
+
+pass "malformed Module.symvers reported against the offending line"
-- 
2.53.0-Meta