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, 514 insertions, 0 deletions

diff --git a/lib/tests/memcpy_kunit.c b/lib/tests/memcpy_kunit.c
new file mode 100644
index 000000000..d36933554
--- /dev/null
+++ b/lib/tests/memcpy_kunit.c
@@ -0,0 +1,514 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test cases for memcpy(), memmove(), and memset().
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <kunit/test.h>
+#include <linux/device.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/overflow.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/vmalloc.h>
+
+struct some_bytes {
+	union {
+		u8 data[32];
+		struct {
+			u32 one;
+			u16 two;
+			u8  three;
+			/* 1 byte hole */
+			u32 four[4];
+		};
+	};
+};
+
+#define check(instance, v) do {	\
+	BUILD_BUG_ON(sizeof(instance.data) != 32);	\
+	for (size_t i = 0; i < sizeof(instance.data); i++) {	\
+		KUNIT_ASSERT_EQ_MSG(test, instance.data[i], v, \
+			"line %d: '%s' not initialized to 0x%02x @ %zu (saw 0x%02x)\n", \
+			__LINE__, #instance, v, i, instance.data[i]);	\
+	}	\
+} while (0)
+
+#define compare(name, one, two) do { \
+	BUILD_BUG_ON(sizeof(one) != sizeof(two)); \
+	for (size_t i = 0; i < sizeof(one); i++) {	\
+		KUNIT_EXPECT_EQ_MSG(test, one.data[i], two.data[i], \
+			"line %d: %s.data[%zu] (0x%02x) != %s.data[%zu] (0x%02x)\n", \
+			__LINE__, #one, i, one.data[i], #two, i, two.data[i]); \
+	}	\
+	kunit_info(test, "ok: " TEST_OP "() " name "\n");	\
+} while (0)
+
+static void memcpy_test(struct kunit *test)
+{
+#define TEST_OP "memcpy"
+	struct some_bytes control = {
+		.data = { 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
+			  0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
+			  0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
+			  0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
+			},
+	};
+	struct some_bytes zero = { };
+	struct some_bytes middle = {
+		.data = { 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
+			  0x20, 0x20, 0x20, 0x20, 0x00, 0x00, 0x00, 0x00,
+			  0x00, 0x00, 0x00, 0x20, 0x20, 0x20, 0x20, 0x20,
+			  0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
+			},
+	};
+	struct some_bytes three = {
+		.data = { 0x00, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
+			  0x20, 0x00, 0x00, 0x20, 0x20, 0x20, 0x20, 0x20,
+			  0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
+			  0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
+			},
+	};
+	struct some_bytes dest = { };
+	int count;
+	u8 *ptr;
+
+	/* Verify static initializers. */
+	check(control, 0x20);
+	check(zero, 0);
+	compare("static initializers", dest, zero);
+
+	/* Verify assignment. */
+	dest = control;
+	compare("direct assignment", dest, control);
+
+	/* Verify complete overwrite. */
+	memcpy(dest.data, zero.data, sizeof(dest.data));
+	compare("complete overwrite", dest, zero);
+
+	/* Verify middle overwrite. */
+	dest = control;
+	memcpy(dest.data + 12, zero.data, 7);
+	compare("middle overwrite", dest, middle);
+
+	/* Verify argument side-effects aren't repeated. */
+	dest = control;
+	ptr = dest.data;
+	count = 1;
+	memcpy(ptr++, zero.data, count++);
+	ptr += 8;
+	memcpy(ptr++, zero.data, count++);
+	compare("argument side-effects", dest, three);
+#undef TEST_OP
+}
+
+static unsigned char larger_array [2048];
+
+static void memmove_test(struct kunit *test)
+{
+#define TEST_OP "memmove"
+	struct some_bytes control = {
+		.data = { 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99,
+			  0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99,
+			  0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99,
+			  0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99,
+			},
+	};
+	struct some_bytes zero = { };
+	struct some_bytes middle = {
+		.data = { 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99,
+			  0x99, 0x99, 0x99, 0x99, 0x00, 0x00, 0x00, 0x00,
+			  0x00, 0x00, 0x00, 0x99, 0x99, 0x99, 0x99, 0x99,
+			  0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99,
+			},
+	};
+	struct some_bytes five = {
+		.data = { 0x00, 0x00, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99,
+			  0x99, 0x99, 0x00, 0x00, 0x00, 0x99, 0x99, 0x99,
+			  0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99,
+			  0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99,
+			},
+	};
+	struct some_bytes overlap = {
+		.data = { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+			  0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F,
+			  0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99,
+			  0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99,
+			},
+	};
+	struct some_bytes overlap_expected = {
+		.data = { 0x00, 0x01, 0x00, 0x01, 0x02, 0x03, 0x04, 0x07,
+			  0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F,
+			  0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99,
+			  0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99,
+			},
+	};
+	struct some_bytes dest = { };
+	int count;
+	u8 *ptr;
+
+	/* Verify static initializers. */
+	check(control, 0x99);
+	check(zero, 0);
+	compare("static initializers", zero, dest);
+
+	/* Verify assignment. */
+	dest = control;
+	compare("direct assignment", dest, control);
+
+	/* Verify complete overwrite. */
+	memmove(dest.data, zero.data, sizeof(dest.data));
+	compare("complete overwrite", dest, zero);
+
+	/* Verify middle overwrite. */
+	dest = control;
+	memmove(dest.data + 12, zero.data, 7);
+	compare("middle overwrite", dest, middle);
+
+	/* Verify argument side-effects aren't repeated. */
+	dest = control;
+	ptr = dest.data;
+	count = 2;
+	memmove(ptr++, zero.data, count++);
+	ptr += 9;
+	memmove(ptr++, zero.data, count++);
+	compare("argument side-effects", dest, five);
+
+	/* Verify overlapping overwrite is correct. */
+	ptr = &overlap.data[2];
+	memmove(ptr, overlap.data, 5);
+	compare("overlapping write", overlap, overlap_expected);
+
+	/* Verify larger overlapping moves. */
+	larger_array[256] = 0xAAu;
+	/*
+	 * Test a backwards overlapping memmove first. 256 and 1024 are
+	 * important for i386 to use rep movsl.
+	 */
+	memmove(larger_array, larger_array + 256, 1024);
+	KUNIT_ASSERT_EQ(test, larger_array[0], 0xAAu);
+	KUNIT_ASSERT_EQ(test, larger_array[256], 0x00);
+	KUNIT_ASSERT_NULL(test,
+		memchr(larger_array + 1, 0xaa, ARRAY_SIZE(larger_array) - 1));
+	/* Test a forwards overlapping memmove. */
+	larger_array[0] = 0xBBu;
+	memmove(larger_array + 256, larger_array, 1024);
+	KUNIT_ASSERT_EQ(test, larger_array[0], 0xBBu);
+	KUNIT_ASSERT_EQ(test, larger_array[256], 0xBBu);
+	KUNIT_ASSERT_NULL(test, memchr(larger_array + 1, 0xBBu, 256 - 1));
+	KUNIT_ASSERT_NULL(test,
+		memchr(larger_array + 257, 0xBBu, ARRAY_SIZE(larger_array) - 257));
+#undef TEST_OP
+}
+
+static void memset_test(struct kunit *test)
+{
+#define TEST_OP "memset"
+	struct some_bytes control = {
+		.data = { 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30,
+			  0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30,
+			  0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30,
+			  0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30,
+			},
+	};
+	struct some_bytes complete = {
+		.data = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+			  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+			  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+			  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+			},
+	};
+	struct some_bytes middle = {
+		.data = { 0x30, 0x30, 0x30, 0x30, 0x31, 0x31, 0x31, 0x31,
+			  0x31, 0x31, 0x31, 0x31, 0x31, 0x31, 0x31, 0x31,
+			  0x31, 0x31, 0x31, 0x31, 0x30, 0x30, 0x30, 0x30,
+			  0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30,
+			},
+	};
+	struct some_bytes three = {
+		.data = { 0x60, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30,
+			  0x30, 0x61, 0x61, 0x30, 0x30, 0x30, 0x30, 0x30,
+			  0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30,
+			  0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30,
+			},
+	};
+	struct some_bytes after = {
+		.data = { 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x72,
+			  0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72,
+			  0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72,
+			  0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72,
+			},
+	};
+	struct some_bytes startat = {
+		.data = { 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30,
+			  0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79,
+			  0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79,
+			  0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79,
+			},
+	};
+	struct some_bytes dest = { };
+	int count, value;
+	u8 *ptr;
+
+	/* Verify static initializers. */
+	check(control, 0x30);
+	check(dest, 0);
+
+	/* Verify assignment. */
+	dest = control;
+	compare("direct assignment", dest, control);
+
+	/* Verify complete overwrite. */
+	memset(dest.data, 0xff, sizeof(dest.data));
+	compare("complete overwrite", dest, complete);
+
+	/* Verify middle overwrite. */
+	dest = control;
+	memset(dest.data + 4, 0x31, 16);
+	compare("middle overwrite", dest, middle);
+
+	/* Verify argument side-effects aren't repeated. */
+	dest = control;
+	ptr = dest.data;
+	value = 0x60;
+	count = 1;
+	memset(ptr++, value++, count++);
+	ptr += 8;
+	memset(ptr++, value++, count++);
+	compare("argument side-effects", dest, three);
+
+	/* Verify memset_after() */
+	dest = control;
+	memset_after(&dest, 0x72, three);
+	compare("memset_after()", dest, after);
+
+	/* Verify memset_startat() */
+	dest = control;
+	memset_startat(&dest, 0x79, four);
+	compare("memset_startat()", dest, startat);
+#undef TEST_OP
+}
+
+static u8 large_src[1024];
+static u8 large_dst[2048];
+static const u8 large_zero[2048];
+
+static void set_random_nonzero(struct kunit *test, u8 *byte)
+{
+	int failed_rng = 0;
+
+	while (*byte == 0) {
+		get_random_bytes(byte, 1);
+		KUNIT_ASSERT_LT_MSG(test, failed_rng++, 100,
+				    "Is the RNG broken?");
+	}
+}
+
+static void init_large(struct kunit *test)
+{
+	/* Get many bit patterns. */
+	get_random_bytes(large_src, ARRAY_SIZE(large_src));
+
+	/* Make sure we have non-zero edges. */
+	set_random_nonzero(test, &large_src[0]);
+	set_random_nonzero(test, &large_src[ARRAY_SIZE(large_src) - 1]);
+
+	/* Explicitly zero the entire destination. */
+	memset(large_dst, 0, ARRAY_SIZE(large_dst));
+}
+
+/*
+ * Instead of an indirect function call for "copy" or a giant macro,
+ * use a bool to pick memcpy or memmove.
+ */
+static void copy_large_test(struct kunit *test, bool use_memmove)
+{
+	init_large(test);
+
+	/* Copy a growing number of non-overlapping bytes ... */
+	for (int bytes = 1; bytes <= ARRAY_SIZE(large_src); bytes++) {
+		/* Over a shifting destination window ... */
+		for (int offset = 0; offset < ARRAY_SIZE(large_src); offset++) {
+			int right_zero_pos = offset + bytes;
+			int right_zero_size = ARRAY_SIZE(large_dst) - right_zero_pos;
+
+			/* Copy! */
+			if (use_memmove)
+				memmove(large_dst + offset, large_src, bytes);
+			else
+				memcpy(large_dst + offset, large_src, bytes);
+
+			/* Did we touch anything before the copy area? */
+			KUNIT_ASSERT_EQ_MSG(test,
+				memcmp(large_dst, large_zero, offset), 0,
+				"with size %d at offset %d", bytes, offset);
+			/* Did we touch anything after the copy area? */
+			KUNIT_ASSERT_EQ_MSG(test,
+				memcmp(&large_dst[right_zero_pos], large_zero, right_zero_size), 0,
+				"with size %d at offset %d", bytes, offset);
+
+			/* Are we byte-for-byte exact across the copy? */
+			KUNIT_ASSERT_EQ_MSG(test,
+				memcmp(large_dst + offset, large_src, bytes), 0,
+				"with size %d at offset %d", bytes, offset);
+
+			/* Zero out what we copied for the next cycle. */
+			memset(large_dst + offset, 0, bytes);
+		}
+		/* Avoid stall warnings if this loop gets slow. */
+		cond_resched();
+	}
+}
+
+static void memcpy_large_test(struct kunit *test)
+{
+	copy_large_test(test, false);
+}
+
+static void memmove_large_test(struct kunit *test)
+{
+	copy_large_test(test, true);
+}
+
+/*
+ * On the assumption that boundary conditions are going to be the most
+ * sensitive, instead of taking a full step (inc) each iteration,
+ * take single index steps for at least the first "inc"-many indexes
+ * from the "start" and at least the last "inc"-many indexes before
+ * the "end". When in the middle, take full "inc"-wide steps. For
+ * example, calling next_step(idx, 1, 15, 3) with idx starting at 0
+ * would see the following pattern: 1 2 3 4 7 10 11 12 13 14 15.
+ */
+static int next_step(int idx, int start, int end, int inc)
+{
+	start += inc;
+	end -= inc;
+
+	if (idx < start || idx + inc > end)
+		inc = 1;
+	return idx + inc;
+}
+
+static void inner_loop(struct kunit *test, int bytes, int d_off, int s_off)
+{
+	int left_zero_pos, left_zero_size;
+	int right_zero_pos, right_zero_size;
+	int src_pos, src_orig_pos, src_size;
+	int pos;
+
+	/* Place the source in the destination buffer. */
+	memcpy(&large_dst[s_off], large_src, bytes);
+
+	/* Copy to destination offset. */
+	memmove(&large_dst[d_off], &large_dst[s_off], bytes);
+
+	/* Make sure destination entirely matches. */
+	KUNIT_ASSERT_EQ_MSG(test, memcmp(&large_dst[d_off], large_src, bytes), 0,
+		"with size %d at src offset %d and dest offset %d",
+		bytes, s_off, d_off);
+
+	/* Calculate the expected zero spans. */
+	if (s_off < d_off) {
+		left_zero_pos = 0;
+		left_zero_size = s_off;
+
+		right_zero_pos = d_off + bytes;
+		right_zero_size = ARRAY_SIZE(large_dst) - right_zero_pos;
+
+		src_pos = s_off;
+		src_orig_pos = 0;
+		src_size = d_off - s_off;
+	} else {
+		left_zero_pos = 0;
+		left_zero_size = d_off;
+
+		right_zero_pos = s_off + bytes;
+		right_zero_size = ARRAY_SIZE(large_dst) - right_zero_pos;
+
+		src_pos = d_off + bytes;
+		src_orig_pos = src_pos - s_off;
+		src_size = right_zero_pos - src_pos;
+	}
+
+	/* Check non-overlapping source is unchanged.*/
+	KUNIT_ASSERT_EQ_MSG(test,
+		memcmp(&large_dst[src_pos], &large_src[src_orig_pos], src_size), 0,
+		"with size %d at src offset %d and dest offset %d",
+		bytes, s_off, d_off);
+
+	/* Check leading buffer contents are zero. */
+	KUNIT_ASSERT_EQ_MSG(test,
+		memcmp(&large_dst[left_zero_pos], large_zero, left_zero_size), 0,
+		"with size %d at src offset %d and dest offset %d",
+		bytes, s_off, d_off);
+	/* Check trailing buffer contents are zero. */
+	KUNIT_ASSERT_EQ_MSG(test,
+		memcmp(&large_dst[right_zero_pos], large_zero, right_zero_size), 0,
+		"with size %d at src offset %d and dest offset %d",
+		bytes, s_off, d_off);
+
+	/* Zero out everything not already zeroed.*/
+	pos = left_zero_pos + left_zero_size;
+	memset(&large_dst[pos], 0, right_zero_pos - pos);
+}
+
+static void memmove_overlap_test(struct kunit *test)
+{
+	/*
+	 * Running all possible offset and overlap combinations takes a
+	 * very long time. Instead, only check up to 128 bytes offset
+	 * into the destination buffer (which should result in crossing
+	 * cachelines), with a step size of 1 through 7 to try to skip some
+	 * redundancy.
+	 */
+	static const int offset_max = 128; /* less than ARRAY_SIZE(large_src); */
+	static const int bytes_step = 7;
+	static const int window_step = 7;
+
+	static const int bytes_start = 1;
+	static const int bytes_end = ARRAY_SIZE(large_src) + 1;
+
+	init_large(test);
+
+	/* Copy a growing number of overlapping bytes ... */
+	for (int bytes = bytes_start; bytes < bytes_end;
+	     bytes = next_step(bytes, bytes_start, bytes_end, bytes_step)) {
+
+		/* Over a shifting destination window ... */
+		for (int d_off = 0; d_off < offset_max; d_off++) {
+			int s_start = max(d_off - bytes, 0);
+			int s_end = min_t(int, d_off + bytes, ARRAY_SIZE(large_src));
+
+			/* Over a shifting source window ... */
+			for (int s_off = s_start; s_off < s_end;
+			     s_off = next_step(s_off, s_start, s_end, window_step))
+				inner_loop(test, bytes, d_off, s_off);
+
+			/* Avoid stall warnings. */
+			cond_resched();
+		}
+	}
+}
+
+static struct kunit_case memcpy_test_cases[] = {
+	KUNIT_CASE(memset_test),
+	KUNIT_CASE(memcpy_test),
+	KUNIT_CASE_SLOW(memcpy_large_test),
+	KUNIT_CASE_SLOW(memmove_test),
+	KUNIT_CASE_SLOW(memmove_large_test),
+	KUNIT_CASE_SLOW(memmove_overlap_test),
+	{}
+};
+
+static struct kunit_suite memcpy_test_suite = {
+	.name = "memcpy",
+	.test_cases = memcpy_test_cases,
+};
+
+kunit_test_suite(memcpy_test_suite);
+
+MODULE_DESCRIPTION("test cases for memcpy(), memmove(), and memset()");
+MODULE_LICENSE("GPL");