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, 294 insertions, 0 deletions

diff --git a/lib/tests/base64_kunit.c b/lib/tests/base64_kunit.c
new file mode 100644
index 000000000..f7252070c
--- /dev/null
+++ b/lib/tests/base64_kunit.c
@@ -0,0 +1,294 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * base64_kunit_test.c - KUnit tests for base64 encoding and decoding functions
+ *
+ * Copyright (c) 2025, Guan-Chun Wu <409411716@gms.tku.edu.tw>
+ */
+
+#include <kunit/test.h>
+#include <linux/base64.h>
+
+/* ---------- Benchmark helpers ---------- */
+static u64 bench_encode_ns(const u8 *data, int len, char *dst, int reps,
+			   enum base64_variant variant)
+{
+	u64 t0, t1;
+
+	t0 = ktime_get_ns();
+	for (int i = 0; i < reps; i++)
+		base64_encode(data, len, dst, true, variant);
+	t1 = ktime_get_ns();
+
+	return div64_u64(t1 - t0, (u64)reps);
+}
+
+static u64 bench_decode_ns(const char *data, int len, u8 *dst, int reps,
+			   enum base64_variant variant)
+{
+	u64 t0, t1;
+
+	t0 = ktime_get_ns();
+	for (int i = 0; i < reps; i++)
+		base64_decode(data, len, dst, true, variant);
+	t1 = ktime_get_ns();
+
+	return div64_u64(t1 - t0, (u64)reps);
+}
+
+static void run_perf_and_check(struct kunit *test, const char *label, int size,
+			       enum base64_variant variant)
+{
+	const int reps = 1000;
+	size_t outlen = DIV_ROUND_UP(size, 3) * 4;
+	u8 *in = kmalloc(size, GFP_KERNEL);
+	char *enc = kmalloc(outlen, GFP_KERNEL);
+	u8 *decoded = kmalloc(size, GFP_KERNEL);
+
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, in);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, enc);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, decoded);
+
+	get_random_bytes(in, size);
+	int enc_len = base64_encode(in, size, enc, true, variant);
+	int dec_len = base64_decode(enc, enc_len, decoded, true, variant);
+
+	/* correctness sanity check */
+	KUNIT_EXPECT_EQ(test, dec_len, size);
+	KUNIT_EXPECT_MEMEQ(test, decoded, in, size);
+
+	/* benchmark encode */
+
+	u64 t1 = bench_encode_ns(in, size, enc, reps, variant);
+
+	kunit_info(test, "[%s] encode run : %lluns", label, t1);
+
+	u64 t2 = bench_decode_ns(enc, enc_len, decoded, reps, variant);
+
+	kunit_info(test, "[%s] decode run : %lluns", label, t2);
+
+	kfree(in);
+	kfree(enc);
+	kfree(decoded);
+}
+
+static void base64_performance_tests(struct kunit *test)
+{
+	/* run on STD variant only */
+	run_perf_and_check(test, "64B", 64, BASE64_STD);
+	run_perf_and_check(test, "1KB", 1024, BASE64_STD);
+}
+
+/* ---------- Helpers for encode ---------- */
+static void expect_encode_ok(struct kunit *test, const u8 *src, int srclen,
+			     const char *expected, bool padding,
+			     enum base64_variant variant)
+{
+	char buf[128];
+	int encoded_len = base64_encode(src, srclen, buf, padding, variant);
+
+	buf[encoded_len] = '\0';
+
+	KUNIT_EXPECT_EQ(test, encoded_len, strlen(expected));
+	KUNIT_EXPECT_STREQ(test, buf, expected);
+}
+
+/* ---------- Helpers for decode ---------- */
+static void expect_decode_ok(struct kunit *test, const char *src,
+			     const u8 *expected, int expected_len, bool padding,
+			     enum base64_variant variant)
+{
+	u8 buf[128];
+	int decoded_len = base64_decode(src, strlen(src), buf, padding, variant);
+
+	KUNIT_EXPECT_EQ(test, decoded_len, expected_len);
+	KUNIT_EXPECT_MEMEQ(test, buf, expected, expected_len);
+}
+
+static void expect_decode_err(struct kunit *test, const char *src,
+			      int srclen, bool padding,
+			      enum base64_variant variant)
+{
+	u8 buf[64];
+	int decoded_len = base64_decode(src, srclen, buf, padding, variant);
+
+	KUNIT_EXPECT_EQ(test, decoded_len, -1);
+}
+
+/* ---------- Encode Tests ---------- */
+static void base64_std_encode_tests(struct kunit *test)
+{
+	/* With padding */
+	expect_encode_ok(test, (const u8 *)"", 0, "", true, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"f", 1, "Zg==", true, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"fo", 2, "Zm8=", true, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"foo", 3, "Zm9v", true, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"foob", 4, "Zm9vYg==", true, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"fooba", 5, "Zm9vYmE=", true, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"foobar", 6, "Zm9vYmFy", true, BASE64_STD);
+
+	/* Extra cases with padding */
+	expect_encode_ok(test, (const u8 *)"Hello, world!", 13, "SGVsbG8sIHdvcmxkIQ==",
+			 true, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"ABCDEFGHIJKLMNOPQRSTUVWXYZ", 26,
+			 "QUJDREVGR0hJSktMTU5PUFFSU1RVVldYWVo=", true, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"abcdefghijklmnopqrstuvwxyz", 26,
+			 "YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXo=", true, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"0123456789+/", 12, "MDEyMzQ1Njc4OSsv",
+			 true, BASE64_STD);
+
+	/* Without padding */
+	expect_encode_ok(test, (const u8 *)"", 0, "", false, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"f", 1, "Zg", false, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"fo", 2, "Zm8", false, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"foo", 3, "Zm9v", false, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"foob", 4, "Zm9vYg", false, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"fooba", 5, "Zm9vYmE", false, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"foobar", 6, "Zm9vYmFy", false, BASE64_STD);
+
+	/* Extra cases without padding */
+	expect_encode_ok(test, (const u8 *)"Hello, world!", 13, "SGVsbG8sIHdvcmxkIQ",
+			 false, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"ABCDEFGHIJKLMNOPQRSTUVWXYZ", 26,
+			 "QUJDREVGR0hJSktMTU5PUFFSU1RVVldYWVo", false, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"abcdefghijklmnopqrstuvwxyz", 26,
+			 "YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXo", false, BASE64_STD);
+	expect_encode_ok(test, (const u8 *)"0123456789+/", 12, "MDEyMzQ1Njc4OSsv",
+			 false, BASE64_STD);
+}
+
+/* ---------- Decode Tests ---------- */
+static void base64_std_decode_tests(struct kunit *test)
+{
+	/* -------- With padding --------*/
+	expect_decode_ok(test, "", (const u8 *)"", 0, true, BASE64_STD);
+	expect_decode_ok(test, "Zg==", (const u8 *)"f", 1, true, BASE64_STD);
+	expect_decode_ok(test, "Zm8=", (const u8 *)"fo", 2, true, BASE64_STD);
+	expect_decode_ok(test, "Zm9v", (const u8 *)"foo", 3, true, BASE64_STD);
+	expect_decode_ok(test, "Zm9vYg==", (const u8 *)"foob", 4, true, BASE64_STD);
+	expect_decode_ok(test, "Zm9vYmE=", (const u8 *)"fooba", 5, true, BASE64_STD);
+	expect_decode_ok(test, "Zm9vYmFy", (const u8 *)"foobar", 6, true, BASE64_STD);
+	expect_decode_ok(test, "SGVsbG8sIHdvcmxkIQ==", (const u8 *)"Hello, world!", 13,
+			 true, BASE64_STD);
+	expect_decode_ok(test, "QUJDREVGR0hJSktMTU5PUFFSU1RVVldYWVo=",
+			 (const u8 *)"ABCDEFGHIJKLMNOPQRSTUVWXYZ", 26, true, BASE64_STD);
+	expect_decode_ok(test, "YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXo=",
+			 (const u8 *)"abcdefghijklmnopqrstuvwxyz", 26, true, BASE64_STD);
+
+	/* Error cases */
+	expect_decode_err(test, "Zg=!", 4, true, BASE64_STD);
+	expect_decode_err(test, "Zm$=", 4, true, BASE64_STD);
+	expect_decode_err(test, "Z===", 4, true, BASE64_STD);
+	expect_decode_err(test, "Zg", 2, true, BASE64_STD);
+	expect_decode_err(test, "Zm9v====", 8, true, BASE64_STD);
+	expect_decode_err(test, "Zm==A", 5, true, BASE64_STD);
+
+	{
+		char with_nul[4] = { 'Z', 'g', '\0', '=' };
+
+		expect_decode_err(test, with_nul, 4, true, BASE64_STD);
+	}
+
+	/* -------- Without padding --------*/
+	expect_decode_ok(test, "", (const u8 *)"", 0, false, BASE64_STD);
+	expect_decode_ok(test, "Zg", (const u8 *)"f", 1, false, BASE64_STD);
+	expect_decode_ok(test, "Zm8", (const u8 *)"fo", 2, false, BASE64_STD);
+	expect_decode_ok(test, "Zm9v", (const u8 *)"foo", 3, false, BASE64_STD);
+	expect_decode_ok(test, "Zm9vYg", (const u8 *)"foob", 4, false, BASE64_STD);
+	expect_decode_ok(test, "Zm9vYmE", (const u8 *)"fooba", 5, false, BASE64_STD);
+	expect_decode_ok(test, "Zm9vYmFy", (const u8 *)"foobar", 6, false, BASE64_STD);
+	expect_decode_ok(test, "TWFu", (const u8 *)"Man", 3, false, BASE64_STD);
+	expect_decode_ok(test, "SGVsbG8sIHdvcmxkIQ", (const u8 *)"Hello, world!", 13,
+			 false, BASE64_STD);
+	expect_decode_ok(test, "QUJDREVGR0hJSktMTU5PUFFSU1RVVldYWVo",
+			 (const u8 *)"ABCDEFGHIJKLMNOPQRSTUVWXYZ", 26, false, BASE64_STD);
+	expect_decode_ok(test, "YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXo",
+			 (const u8 *)"abcdefghijklmnopqrstuvwxyz", 26, false, BASE64_STD);
+	expect_decode_ok(test, "MDEyMzQ1Njc4OSsv", (const u8 *)"0123456789+/", 12,
+			 false, BASE64_STD);
+
+	/* Error cases */
+	expect_decode_err(test, "Zg=!", 4, false, BASE64_STD);
+	expect_decode_err(test, "Zm$=", 4, false, BASE64_STD);
+	expect_decode_err(test, "Z===", 4, false, BASE64_STD);
+	expect_decode_err(test, "Zg=", 3, false, BASE64_STD);
+	expect_decode_err(test, "Zm9v====", 8, false, BASE64_STD);
+	expect_decode_err(test, "Zm==v", 4, false, BASE64_STD);
+
+	{
+		char with_nul[4] = { 'Z', 'g', '\0', '=' };
+
+		expect_decode_err(test, with_nul, 4, false, BASE64_STD);
+	}
+}
+
+/* ---------- Variant tests (URLSAFE / IMAP) ---------- */
+static void base64_variant_tests(struct kunit *test)
+{
+	const u8 sample1[] = { 0x00, 0xfb, 0xff, 0x7f, 0x80 };
+	char std_buf[128], url_buf[128], imap_buf[128];
+	u8 back[128];
+	int n_std, n_url, n_imap, m;
+	int i;
+
+	n_std = base64_encode(sample1, sizeof(sample1), std_buf, false, BASE64_STD);
+	n_url = base64_encode(sample1, sizeof(sample1), url_buf, false, BASE64_URLSAFE);
+	std_buf[n_std] = '\0';
+	url_buf[n_url] = '\0';
+
+	for (i = 0; i < n_std; i++) {
+		if (std_buf[i] == '+')
+			std_buf[i] = '-';
+		else if (std_buf[i] == '/')
+			std_buf[i] = '_';
+	}
+	KUNIT_EXPECT_STREQ(test, std_buf, url_buf);
+
+	m = base64_decode(url_buf, n_url, back, false, BASE64_URLSAFE);
+	KUNIT_EXPECT_EQ(test, m, (int)sizeof(sample1));
+	KUNIT_EXPECT_MEMEQ(test, back, sample1, sizeof(sample1));
+
+	n_std  = base64_encode(sample1, sizeof(sample1), std_buf, false, BASE64_STD);
+	n_imap = base64_encode(sample1, sizeof(sample1), imap_buf, false, BASE64_IMAP);
+	std_buf[n_std]   = '\0';
+	imap_buf[n_imap] = '\0';
+
+	for (i = 0; i < n_std; i++)
+		if (std_buf[i] == '/')
+			std_buf[i] = ',';
+	KUNIT_EXPECT_STREQ(test, std_buf, imap_buf);
+
+	m = base64_decode(imap_buf, n_imap, back, false, BASE64_IMAP);
+	KUNIT_EXPECT_EQ(test, m, (int)sizeof(sample1));
+	KUNIT_EXPECT_MEMEQ(test, back, sample1, sizeof(sample1));
+
+	{
+		const char *bad = "Zg==";
+		u8 tmp[8];
+
+		m = base64_decode(bad, strlen(bad), tmp, false, BASE64_URLSAFE);
+		KUNIT_EXPECT_EQ(test, m, -1);
+
+		m = base64_decode(bad, strlen(bad), tmp, false, BASE64_IMAP);
+		KUNIT_EXPECT_EQ(test, m, -1);
+	}
+}
+
+/* ---------- Test registration ---------- */
+static struct kunit_case base64_test_cases[] = {
+	KUNIT_CASE(base64_performance_tests),
+	KUNIT_CASE(base64_std_encode_tests),
+	KUNIT_CASE(base64_std_decode_tests),
+	KUNIT_CASE(base64_variant_tests),
+	{}
+};
+
+static struct kunit_suite base64_test_suite = {
+	.name = "base64",
+	.test_cases = base64_test_cases,
+};
+
+kunit_test_suite(base64_test_suite);
+
+MODULE_AUTHOR("Guan-Chun Wu <409411716@gms.tku.edu.tw>");
+MODULE_DESCRIPTION("KUnit tests for Base64 encoding/decoding, including performance checks");
+MODULE_LICENSE("GPL");