kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 134 insertions, 0 deletions

diff --git a/tools/perf/tests/subcmd-help.c b/tools/perf/tests/subcmd-help.c
new file mode 100644
index 000000000..9da96a16f
--- /dev/null
+++ b/tools/perf/tests/subcmd-help.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "tests.h"
+#include <linux/compiler.h>
+#include <subcmd/help.h>
+
+static int test__load_cmdnames(struct test_suite *test __maybe_unused,
+			       int subtest __maybe_unused)
+{
+	struct cmdnames cmds = {};
+
+	add_cmdname(&cmds, "aaa", 3);
+	add_cmdname(&cmds, "foo", 3);
+	add_cmdname(&cmds, "xyz", 3);
+
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds, "aaa") == 1);
+	TEST_ASSERT_VAL("wrong cmd", is_in_cmdlist(&cmds, "bar") == 0);
+	TEST_ASSERT_VAL("case sensitive", is_in_cmdlist(&cmds, "XYZ") == 0);
+
+	clean_cmdnames(&cmds);
+	return TEST_OK;
+}
+
+static int test__uniq_cmdnames(struct test_suite *test __maybe_unused,
+			       int subtest __maybe_unused)
+{
+	struct cmdnames cmds = {};
+
+	/* uniq() assumes it's sorted */
+	add_cmdname(&cmds, "aaa", 3);
+	add_cmdname(&cmds, "aaa", 3);
+	add_cmdname(&cmds, "bbb", 3);
+
+	TEST_ASSERT_VAL("invalid original size", cmds.cnt == 3);
+	/* uniquify command names (to remove second 'aaa') */
+	uniq(&cmds);
+	TEST_ASSERT_VAL("invalid final size", cmds.cnt == 2);
+
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds, "aaa") == 1);
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds, "bbb") == 1);
+	TEST_ASSERT_VAL("wrong cmd", is_in_cmdlist(&cmds, "ccc") == 0);
+
+	clean_cmdnames(&cmds);
+	return TEST_OK;
+}
+
+static int test__exclude_cmdnames(struct test_suite *test __maybe_unused,
+				  int subtest __maybe_unused)
+{
+	struct cmdnames cmds1 = {};
+	struct cmdnames cmds2 = {};
+
+	add_cmdname(&cmds1, "aaa", 3);
+	add_cmdname(&cmds1, "bbb", 3);
+	add_cmdname(&cmds1, "ccc", 3);
+	add_cmdname(&cmds1, "ddd", 3);
+	add_cmdname(&cmds1, "eee", 3);
+	add_cmdname(&cmds1, "fff", 3);
+	add_cmdname(&cmds1, "ggg", 3);
+	add_cmdname(&cmds1, "hhh", 3);
+	add_cmdname(&cmds1, "iii", 3);
+	add_cmdname(&cmds1, "jjj", 3);
+
+	add_cmdname(&cmds2, "bbb", 3);
+	add_cmdname(&cmds2, "eee", 3);
+	add_cmdname(&cmds2, "jjj", 3);
+
+	TEST_ASSERT_VAL("invalid original size", cmds1.cnt == 10);
+	TEST_ASSERT_VAL("invalid original size", cmds2.cnt == 3);
+
+	/* remove duplicate command names in cmds1 */
+	exclude_cmds(&cmds1, &cmds2);
+
+	TEST_ASSERT_VAL("invalid excluded size", cmds1.cnt == 7);
+	TEST_ASSERT_VAL("invalid excluded size", cmds2.cnt == 3);
+
+	/* excluded commands should not belong to cmds1 */
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds1, "aaa") == 1);
+	TEST_ASSERT_VAL("wrong cmd", is_in_cmdlist(&cmds1, "bbb") == 0);
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds1, "ccc") == 1);
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds1, "ddd") == 1);
+	TEST_ASSERT_VAL("wrong cmd", is_in_cmdlist(&cmds1, "eee") == 0);
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds1, "fff") == 1);
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds1, "ggg") == 1);
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds1, "hhh") == 1);
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds1, "iii") == 1);
+	TEST_ASSERT_VAL("wrong cmd", is_in_cmdlist(&cmds1, "jjj") == 0);
+
+	/* they should be only in cmds2 */
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds2, "bbb") == 1);
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds2, "eee") == 1);
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds2, "jjj") == 1);
+
+	clean_cmdnames(&cmds1);
+	clean_cmdnames(&cmds2);
+	return TEST_OK;
+}
+
+static int test__exclude_cmdnames_no_overlap(struct test_suite *test __maybe_unused,
+					     int subtest __maybe_unused)
+{
+	struct cmdnames cmds1 = {};
+	struct cmdnames cmds2 = {};
+
+	add_cmdname(&cmds1, "read-vdso32", 11);
+	add_cmdname(&cmds2, "archive", 7);
+
+	TEST_ASSERT_VAL("invalid original size", cmds1.cnt == 1);
+	TEST_ASSERT_VAL("invalid original size", cmds2.cnt == 1);
+
+	exclude_cmds(&cmds1, &cmds2);
+
+	TEST_ASSERT_VAL("invalid excluded size", cmds1.cnt == 1);
+	TEST_ASSERT_VAL("invalid excluded size", cmds2.cnt == 1);
+
+	TEST_ASSERT_VAL("cannot find cmd", is_in_cmdlist(&cmds1, "read-vdso32") == 1);
+	TEST_ASSERT_VAL("wrong cmd", is_in_cmdlist(&cmds1, "archive") == 0);
+
+	clean_cmdnames(&cmds1);
+	clean_cmdnames(&cmds2);
+	return TEST_OK;
+}
+
+static struct test_case tests__subcmd_help[] = {
+	TEST_CASE("Load subcmd names", load_cmdnames),
+	TEST_CASE("Uniquify subcmd names", uniq_cmdnames),
+	TEST_CASE("Exclude duplicate subcmd names", exclude_cmdnames),
+	TEST_CASE("Exclude disjoint subcmd names", exclude_cmdnames_no_overlap),
+	{	.name = NULL, }
+};
+
+struct test_suite suite__subcmd_help = {
+	.desc = "libsubcmd help tests",
+	.test_cases = tests__subcmd_help,
+};