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, 178 insertions, 0 deletions

diff --git a/drivers/of/of_test.c b/drivers/of/of_test.c
new file mode 100644
index 000000000..8bba5a72c
--- /dev/null
+++ b/drivers/of/of_test.c
@@ -0,0 +1,178 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit tests for OF APIs
+ */
+#include <linux/ioport.h>
+#include <linux/module.h>
+#include <linux/of.h>
+
+#include <kunit/test.h>
+
+#include "of_private.h"
+
+/*
+ * Test that the root node "/" can be found by path.
+ */
+static void of_dtb_root_node_found_by_path(struct kunit *test)
+{
+	struct device_node *np;
+
+	np = of_find_node_by_path("/");
+	KUNIT_EXPECT_NOT_ERR_OR_NULL(test, np);
+	of_node_put(np);
+}
+
+/*
+ * Test that the 'of_root' global variable is always populated when DT code is
+ * enabled. Remove this test once of_root is removed from global access.
+ */
+static void of_dtb_root_node_populates_of_root(struct kunit *test)
+{
+	KUNIT_EXPECT_NOT_ERR_OR_NULL(test, of_root);
+}
+
+static struct kunit_case of_dtb_test_cases[] = {
+	KUNIT_CASE(of_dtb_root_node_found_by_path),
+	KUNIT_CASE(of_dtb_root_node_populates_of_root),
+	{}
+};
+
+static int of_dtb_test_init(struct kunit *test)
+{
+	of_root_kunit_skip(test);
+	if (!IS_ENABLED(CONFIG_OF_EARLY_FLATTREE))
+		kunit_skip(test, "requires CONFIG_OF_EARLY_FLATTREE");
+
+	return 0;
+}
+
+/*
+ * Test suite to confirm a DTB is loaded.
+ */
+static struct kunit_suite of_dtb_suite = {
+	.name = "of_dtb",
+	.test_cases = of_dtb_test_cases,
+	.init = of_dtb_test_init,
+};
+
+struct of_address_resource_bounds_case {
+	u64 start;
+	u64 size;
+	int ret;
+
+	u64 res_start;
+	u64 res_end;
+};
+
+static void of_address_resource_bounds_case_desc(const struct of_address_resource_bounds_case *p,
+						 char *name)
+{
+	snprintf(name, KUNIT_PARAM_DESC_SIZE, "start=0x%016llx,size=0x%016llx", p->start, p->size);
+}
+
+static const struct of_address_resource_bounds_case of_address_resource_bounds_cases[] = {
+	{
+		.start = 0,
+		.size = 0,
+		.ret = 0,
+		.res_start = 0,
+		.res_end = -1,
+	},
+	{
+		.start = 0,
+		.size = 0x1000,
+		.ret = 0,
+		.res_start = 0,
+		.res_end = 0xfff,
+	},
+	{
+		.start = 0x1000,
+		.size = 0,
+		.ret = 0,
+		.res_start = 0x1000,
+		.res_end = 0xfff,
+	},
+	{
+		.start = 0x1000,
+		.size = 0x1000,
+		.ret = 0,
+		.res_start = 0x1000,
+		.res_end = 0x1fff,
+	},
+	{
+		.start = 1,
+		.size = RESOURCE_SIZE_MAX,
+		.ret = 0,
+		.res_start = 1,
+		.res_end = RESOURCE_SIZE_MAX,
+	},
+	{
+		.start = RESOURCE_SIZE_MAX,
+		.size = 1,
+		.ret = 0,
+		.res_start = RESOURCE_SIZE_MAX,
+		.res_end = RESOURCE_SIZE_MAX,
+	},
+	{
+		.start = 2,
+		.size = RESOURCE_SIZE_MAX,
+		.ret = -EOVERFLOW,
+	},
+	{
+		.start = RESOURCE_SIZE_MAX,
+		.size = 2,
+		.ret = -EOVERFLOW,
+	},
+	{
+		.start = ULL(0x100000000),
+		.size = 1,
+		.ret = sizeof(resource_size_t) > sizeof(u32) ? 0 : -EOVERFLOW,
+		.res_start = ULL(0x100000000),
+		.res_end = ULL(0x100000000),
+	},
+	{
+		.start = 0x1000,
+		.size = 0xffffffff,
+		.ret = sizeof(resource_size_t) > sizeof(u32) ? 0 : -EOVERFLOW,
+		.res_start = 0x1000,
+		.res_end = ULL(0x100000ffe),
+	},
+};
+
+KUNIT_ARRAY_PARAM(of_address_resource_bounds,
+		  of_address_resource_bounds_cases, of_address_resource_bounds_case_desc);
+
+static void of_address_resource_bounds(struct kunit *test)
+{
+	const struct of_address_resource_bounds_case *param = test->param_value;
+	struct resource r; /* Intentionally uninitialized */
+	int ret;
+
+	if (!IS_ENABLED(CONFIG_OF_ADDRESS))
+		kunit_skip(test, "CONFIG_OF_ADDRESS not enabled\n");
+
+	ret = __of_address_resource_bounds(&r, param->start, param->size);
+	KUNIT_EXPECT_EQ(test, param->ret, ret);
+	if (ret == 0) {
+		KUNIT_EXPECT_EQ(test, (resource_size_t)param->res_start, r.start);
+		KUNIT_EXPECT_EQ(test, (resource_size_t)param->res_end, r.end);
+		KUNIT_EXPECT_EQ(test, param->size, resource_size(&r));
+	}
+}
+
+static struct kunit_case of_address_test_cases[] = {
+	KUNIT_CASE_PARAM(of_address_resource_bounds, of_address_resource_bounds_gen_params),
+	{}
+};
+
+static struct kunit_suite of_address_suite = {
+	.name = "of_address",
+	.test_cases = of_address_test_cases,
+};
+
+kunit_test_suites(
+	&of_dtb_suite, &of_address_suite,
+);
+MODULE_DESCRIPTION("KUnit tests for OF APIs");
+MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");
+MODULE_LICENSE("GPL");