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, 163 insertions, 0 deletions

diff --git a/tools/perf/tests/kmod-path.c b/tools/perf/tests/kmod-path.c
new file mode 100644
index 000000000..dfe1bd5da
--- /dev/null
+++ b/tools/perf/tests/kmod-path.c
@@ -0,0 +1,163 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include "tests.h"
+#include "dso.h"
+#include "debug.h"
+#include "event.h"
+
+static int test(const char *path, bool alloc_name, bool kmod,
+		int comp, const char *name)
+{
+	struct kmod_path m;
+
+	memset(&m, 0x0, sizeof(m));
+
+	TEST_ASSERT_VAL("kmod_path__parse",
+			!__kmod_path__parse(&m, path, alloc_name));
+
+	pr_debug("%s - alloc name %d, kmod %d, comp %d, name '%s'\n",
+		 path, alloc_name, m.kmod, m.comp, m.name);
+
+	TEST_ASSERT_VAL("wrong kmod", m.kmod == kmod);
+	TEST_ASSERT_VAL("wrong comp", m.comp == comp);
+
+	if (name)
+		TEST_ASSERT_VAL("wrong name", m.name && !strcmp(name, m.name));
+	else
+		TEST_ASSERT_VAL("wrong name", !m.name);
+
+	free(m.name);
+	return 0;
+}
+
+static int test_is_kernel_module(const char *path, int cpumode, bool expect)
+{
+	TEST_ASSERT_VAL("is_kernel_module",
+			(!!is_kernel_module(path, cpumode)) == (!!expect));
+	pr_debug("%s (cpumode: %d) - is_kernel_module: %s\n",
+			path, cpumode, expect ? "true" : "false");
+	return 0;
+}
+
+#define T(path, an, k, c, n) \
+	TEST_ASSERT_VAL("failed", !test(path, an, k, c, n))
+
+#define M(path, c, e) \
+	TEST_ASSERT_VAL("failed", !test_is_kernel_module(path, c, e))
+
+static int test__kmod_path__parse(struct test_suite *t __maybe_unused, int subtest __maybe_unused)
+{
+	/* path                alloc_name  kmod  comp   name   */
+	T("/xxxx/xxxx/x-x.ko", true      , true, 0    , "[x_x]");
+	T("/xxxx/xxxx/x-x.ko", false     , true, 0    , NULL   );
+	T("/xxxx/xxxx/x-x.ko", true      , true, 0    , "[x_x]");
+	T("/xxxx/xxxx/x-x.ko", false     , true, 0    , NULL   );
+	M("/xxxx/xxxx/x-x.ko", PERF_RECORD_MISC_CPUMODE_UNKNOWN, true);
+	M("/xxxx/xxxx/x-x.ko", PERF_RECORD_MISC_KERNEL, true);
+	M("/xxxx/xxxx/x-x.ko", PERF_RECORD_MISC_USER, false);
+
+#ifdef HAVE_ZLIB_SUPPORT
+	/* path                alloc_name   kmod  comp  name  */
+	T("/xxxx/xxxx/x.ko.gz", true     , true, 1   , "[x]");
+	T("/xxxx/xxxx/x.ko.gz", false    , true, 1   , NULL );
+	T("/xxxx/xxxx/x.ko.gz", true     , true, 1   , "[x]");
+	T("/xxxx/xxxx/x.ko.gz", false    , true, 1   , NULL );
+	M("/xxxx/xxxx/x.ko.gz", PERF_RECORD_MISC_CPUMODE_UNKNOWN, true);
+	M("/xxxx/xxxx/x.ko.gz", PERF_RECORD_MISC_KERNEL, true);
+	M("/xxxx/xxxx/x.ko.gz", PERF_RECORD_MISC_USER, false);
+
+	/* path              alloc_name  kmod   comp  name  */
+	T("/xxxx/xxxx/x.gz", true      , false, 1   , "x.gz");
+	T("/xxxx/xxxx/x.gz", false     , false, 1   , NULL  );
+	T("/xxxx/xxxx/x.gz", true      , false, 1   , "x.gz");
+	T("/xxxx/xxxx/x.gz", false     , false, 1   , NULL  );
+	M("/xxxx/xxxx/x.gz", PERF_RECORD_MISC_CPUMODE_UNKNOWN, false);
+	M("/xxxx/xxxx/x.gz", PERF_RECORD_MISC_KERNEL, false);
+	M("/xxxx/xxxx/x.gz", PERF_RECORD_MISC_USER, false);
+
+	/* path   alloc_name  kmod   comp  name   */
+	T("x.gz", true      , false, 1   , "x.gz");
+	T("x.gz", false     , false, 1   , NULL  );
+	T("x.gz", true      , false, 1   , "x.gz");
+	T("x.gz", false     , false, 1   , NULL  );
+	M("x.gz", PERF_RECORD_MISC_CPUMODE_UNKNOWN, false);
+	M("x.gz", PERF_RECORD_MISC_KERNEL, false);
+	M("x.gz", PERF_RECORD_MISC_USER, false);
+
+	/* path      alloc_name  kmod  comp  name  */
+	T("x.ko.gz", true      , true, 1   , "[x]");
+	T("x.ko.gz", false     , true, 1   , NULL );
+	T("x.ko.gz", true      , true, 1   , "[x]");
+	T("x.ko.gz", false     , true, 1   , NULL );
+	M("x.ko.gz", PERF_RECORD_MISC_CPUMODE_UNKNOWN, true);
+	M("x.ko.gz", PERF_RECORD_MISC_KERNEL, true);
+	M("x.ko.gz", PERF_RECORD_MISC_USER, false);
+#endif
+
+	/* path            alloc_name  kmod  comp   name           */
+	T("[test_module]", true      , true, false, "[test_module]");
+	T("[test_module]", false     , true, false, NULL           );
+	T("[test_module]", true      , true, false, "[test_module]");
+	T("[test_module]", false     , true, false, NULL           );
+	M("[test_module]", PERF_RECORD_MISC_CPUMODE_UNKNOWN, true);
+	M("[test_module]", PERF_RECORD_MISC_KERNEL, true);
+	M("[test_module]", PERF_RECORD_MISC_USER, false);
+
+	/* path            alloc_name  kmod  comp   name           */
+	T("[test.module]", true      , true, false, "[test.module]");
+	T("[test.module]", false     , true, false, NULL           );
+	T("[test.module]", true      , true, false, "[test.module]");
+	T("[test.module]", false     , true, false, NULL           );
+	M("[test.module]", PERF_RECORD_MISC_CPUMODE_UNKNOWN, true);
+	M("[test.module]", PERF_RECORD_MISC_KERNEL, true);
+	M("[test.module]", PERF_RECORD_MISC_USER, false);
+
+	/* path     alloc_name  kmod   comp   name    */
+	T("[vdso]", true      , false, false, "[vdso]");
+	T("[vdso]", false     , false, false, NULL    );
+	T("[vdso]", true      , false, false, "[vdso]");
+	T("[vdso]", false     , false, false, NULL    );
+	M("[vdso]", PERF_RECORD_MISC_CPUMODE_UNKNOWN, false);
+	M("[vdso]", PERF_RECORD_MISC_KERNEL, false);
+	M("[vdso]", PERF_RECORD_MISC_USER, false);
+
+	T("[vdso32]", true      , false, false, "[vdso32]");
+	T("[vdso32]", false     , false, false, NULL      );
+	T("[vdso32]", true      , false, false, "[vdso32]");
+	T("[vdso32]", false     , false, false, NULL      );
+	M("[vdso32]", PERF_RECORD_MISC_CPUMODE_UNKNOWN, false);
+	M("[vdso32]", PERF_RECORD_MISC_KERNEL, false);
+	M("[vdso32]", PERF_RECORD_MISC_USER, false);
+
+	T("[vdsox32]", true      , false, false, "[vdsox32]");
+	T("[vdsox32]", false     , false, false, NULL       );
+	T("[vdsox32]", true      , false, false, "[vdsox32]");
+	T("[vdsox32]", false     , false, false, NULL       );
+	M("[vdsox32]", PERF_RECORD_MISC_CPUMODE_UNKNOWN, false);
+	M("[vdsox32]", PERF_RECORD_MISC_KERNEL, false);
+	M("[vdsox32]", PERF_RECORD_MISC_USER, false);
+
+	/* path         alloc_name  kmod   comp   name        */
+	T("[vsyscall]", true      , false, false, "[vsyscall]");
+	T("[vsyscall]", false     , false, false, NULL        );
+	T("[vsyscall]", true      , false, false, "[vsyscall]");
+	T("[vsyscall]", false     , false, false, NULL        );
+	M("[vsyscall]", PERF_RECORD_MISC_CPUMODE_UNKNOWN, false);
+	M("[vsyscall]", PERF_RECORD_MISC_KERNEL, false);
+	M("[vsyscall]", PERF_RECORD_MISC_USER, false);
+
+	/* path                alloc_name  kmod   comp   name      */
+	T("[kernel.kallsyms]", true      , false, false, "[kernel.kallsyms]");
+	T("[kernel.kallsyms]", false     , false, false, NULL               );
+	T("[kernel.kallsyms]", true      , false, false, "[kernel.kallsyms]");
+	T("[kernel.kallsyms]", false     , false, false, NULL               );
+	M("[kernel.kallsyms]", PERF_RECORD_MISC_CPUMODE_UNKNOWN, false);
+	M("[kernel.kallsyms]", PERF_RECORD_MISC_KERNEL, false);
+	M("[kernel.kallsyms]", PERF_RECORD_MISC_USER, false);
+
+	return 0;
+}
+
+DEFINE_SUITE("kmod_path__parse", kmod_path__parse);