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, 283 insertions, 0 deletions

diff --git a/fs/ext4/inode-test.c b/fs/ext4/inode-test.c
new file mode 100644
index 000000000..749af7ad4
--- /dev/null
+++ b/fs/ext4/inode-test.c
@@ -0,0 +1,283 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test of ext4 inode that verify the seconds part of [a/c/m]
+ * timestamps in ext4 inode structs are decoded correctly.
+ */
+
+#include <kunit/test.h>
+#include <linux/kernel.h>
+#include <linux/time64.h>
+
+#include "ext4.h"
+
+/*
+ * For constructing the nonnegative timestamp lower bound value.
+ * binary: 00000000 00000000 00000000 00000000
+ */
+#define LOWER_MSB_0 0L
+/*
+ * For constructing the nonnegative timestamp upper bound value.
+ * binary: 01111111 11111111 11111111 11111111
+ *
+ */
+#define UPPER_MSB_0 0x7fffffffL
+/*
+ * For constructing the negative timestamp lower bound value.
+ * binary: 10000000 00000000 00000000 00000000
+ */
+#define LOWER_MSB_1 (-(UPPER_MSB_0) - 1L)  /* avoid overflow */
+/*
+ * For constructing the negative timestamp upper bound value.
+ * binary: 11111111 11111111 11111111 11111111
+ */
+#define UPPER_MSB_1 (-1L)
+/*
+ * Upper bound for nanoseconds value supported by the encoding.
+ * binary: 00111111 11111111 11111111 11111111
+ */
+#define MAX_NANOSECONDS ((1L << 30) - 1)
+
+#define CASE_NAME_FORMAT "%s: msb:%x lower_bound:%x extra_bits: %x"
+
+#define LOWER_BOUND_NEG_NO_EXTRA_BITS_CASE\
+	"1901-12-13 Lower bound of 32bit < 0 timestamp, no extra bits"
+#define UPPER_BOUND_NEG_NO_EXTRA_BITS_CASE\
+	"1969-12-31 Upper bound of 32bit < 0 timestamp, no extra bits"
+#define LOWER_BOUND_NONNEG_NO_EXTRA_BITS_CASE\
+	"1970-01-01 Lower bound of 32bit >=0 timestamp, no extra bits"
+#define UPPER_BOUND_NONNEG_NO_EXTRA_BITS_CASE\
+	"2038-01-19 Upper bound of 32bit >=0 timestamp, no extra bits"
+#define LOWER_BOUND_NEG_LO_1_CASE\
+	"2038-01-19 Lower bound of 32bit <0 timestamp, lo extra sec bit on"
+#define UPPER_BOUND_NEG_LO_1_CASE\
+	"2106-02-07 Upper bound of 32bit <0 timestamp, lo extra sec bit on"
+#define LOWER_BOUND_NONNEG_LO_1_CASE\
+	"2106-02-07 Lower bound of 32bit >=0 timestamp, lo extra sec bit on"
+#define UPPER_BOUND_NONNEG_LO_1_CASE\
+	"2174-02-25 Upper bound of 32bit >=0 timestamp, lo extra sec bit on"
+#define LOWER_BOUND_NEG_HI_1_CASE\
+	"2174-02-25 Lower bound of 32bit <0 timestamp, hi extra sec bit on"
+#define UPPER_BOUND_NEG_HI_1_CASE\
+	"2242-03-16 Upper bound of 32bit <0 timestamp, hi extra sec bit on"
+#define LOWER_BOUND_NONNEG_HI_1_CASE\
+	"2242-03-16 Lower bound of 32bit >=0 timestamp, hi extra sec bit on"
+#define UPPER_BOUND_NONNEG_HI_1_CASE\
+	"2310-04-04 Upper bound of 32bit >=0 timestamp, hi extra sec bit on"
+#define UPPER_BOUND_NONNEG_HI_1_NS_1_CASE\
+	"2310-04-04 Upper bound of 32bit>=0 timestamp, hi extra sec bit 1. 1 ns"
+#define LOWER_BOUND_NONNEG_HI_1_NS_MAX_CASE\
+	"2378-04-22 Lower bound of 32bit>= timestamp. Extra sec bits 1. Max ns"
+#define LOWER_BOUND_NONNEG_EXTRA_BITS_1_CASE\
+	"2378-04-22 Lower bound of 32bit >=0 timestamp. All extra sec bits on"
+#define UPPER_BOUND_NONNEG_EXTRA_BITS_1_CASE\
+	"2446-05-10 Upper bound of 32bit >=0 timestamp. All extra sec bits on"
+
+struct timestamp_expectation {
+	const char *test_case_name;
+	struct timespec64 expected;
+	u32 extra_bits;
+	bool msb_set;
+	bool lower_bound;
+};
+
+static const struct timestamp_expectation test_data[] = {
+	{
+		.test_case_name = LOWER_BOUND_NEG_NO_EXTRA_BITS_CASE,
+		.msb_set = true,
+		.lower_bound = true,
+		.extra_bits = 0,
+		.expected = {.tv_sec = -0x80000000LL, .tv_nsec = 0L},
+	},
+
+	{
+		.test_case_name = UPPER_BOUND_NEG_NO_EXTRA_BITS_CASE,
+		.msb_set = true,
+		.lower_bound = false,
+		.extra_bits = 0,
+		.expected = {.tv_sec = -1LL, .tv_nsec = 0L},
+	},
+
+	{
+		.test_case_name = LOWER_BOUND_NONNEG_NO_EXTRA_BITS_CASE,
+		.msb_set = false,
+		.lower_bound = true,
+		.extra_bits = 0,
+		.expected = {0LL, 0L},
+	},
+
+	{
+		.test_case_name = UPPER_BOUND_NONNEG_NO_EXTRA_BITS_CASE,
+		.msb_set = false,
+		.lower_bound = false,
+		.extra_bits = 0,
+		.expected = {.tv_sec = 0x7fffffffLL, .tv_nsec = 0L},
+	},
+
+	{
+		.test_case_name = LOWER_BOUND_NEG_LO_1_CASE,
+		.msb_set = true,
+		.lower_bound = true,
+		.extra_bits = 1,
+		.expected = {.tv_sec = 0x80000000LL, .tv_nsec = 0L},
+	},
+
+	{
+		.test_case_name = UPPER_BOUND_NEG_LO_1_CASE,
+		.msb_set = true,
+		.lower_bound = false,
+		.extra_bits = 1,
+		.expected = {.tv_sec = 0xffffffffLL, .tv_nsec = 0L},
+	},
+
+	{
+		.test_case_name = LOWER_BOUND_NONNEG_LO_1_CASE,
+		.msb_set = false,
+		.lower_bound = true,
+		.extra_bits = 1,
+		.expected = {.tv_sec = 0x100000000LL, .tv_nsec = 0L},
+	},
+
+	{
+		.test_case_name = UPPER_BOUND_NONNEG_LO_1_CASE,
+		.msb_set = false,
+		.lower_bound = false,
+		.extra_bits = 1,
+		.expected = {.tv_sec = 0x17fffffffLL, .tv_nsec = 0L},
+	},
+
+	{
+		.test_case_name = LOWER_BOUND_NEG_HI_1_CASE,
+		.msb_set = true,
+		.lower_bound = true,
+		.extra_bits =  2,
+		.expected = {.tv_sec = 0x180000000LL, .tv_nsec = 0L},
+	},
+
+	{
+		.test_case_name = UPPER_BOUND_NEG_HI_1_CASE,
+		.msb_set = true,
+		.lower_bound = false,
+		.extra_bits = 2,
+		.expected = {.tv_sec = 0x1ffffffffLL, .tv_nsec = 0L},
+	},
+
+	{
+		.test_case_name = LOWER_BOUND_NONNEG_HI_1_CASE,
+		.msb_set = false,
+		.lower_bound = true,
+		.extra_bits = 2,
+		.expected = {.tv_sec = 0x200000000LL, .tv_nsec = 0L},
+	},
+
+	{
+		.test_case_name = UPPER_BOUND_NONNEG_HI_1_CASE,
+		.msb_set = false,
+		.lower_bound = false,
+		.extra_bits = 2,
+		.expected = {.tv_sec = 0x27fffffffLL, .tv_nsec = 0L},
+	},
+
+	{
+		.test_case_name = UPPER_BOUND_NONNEG_HI_1_NS_1_CASE,
+		.msb_set = false,
+		.lower_bound = false,
+		.extra_bits = 6,
+		.expected = {.tv_sec = 0x27fffffffLL, .tv_nsec = 1L},
+	},
+
+	{
+		.test_case_name = LOWER_BOUND_NONNEG_HI_1_NS_MAX_CASE,
+		.msb_set = false,
+		.lower_bound = true,
+		.extra_bits = 0xFFFFFFFF,
+		.expected = {.tv_sec = 0x300000000LL,
+			     .tv_nsec = MAX_NANOSECONDS},
+	},
+
+	{
+		.test_case_name = LOWER_BOUND_NONNEG_EXTRA_BITS_1_CASE,
+		.msb_set = false,
+		.lower_bound = true,
+		.extra_bits = 3,
+		.expected = {.tv_sec = 0x300000000LL, .tv_nsec = 0L},
+	},
+
+	{
+		.test_case_name = UPPER_BOUND_NONNEG_EXTRA_BITS_1_CASE,
+		.msb_set = false,
+		.lower_bound = false,
+		.extra_bits = 3,
+		.expected = {.tv_sec = 0x37fffffffLL, .tv_nsec = 0L},
+	}
+};
+
+static void timestamp_expectation_to_desc(const struct timestamp_expectation *t,
+					  char *desc)
+{
+	strscpy(desc, t->test_case_name, KUNIT_PARAM_DESC_SIZE);
+}
+
+KUNIT_ARRAY_PARAM(ext4_inode, test_data, timestamp_expectation_to_desc);
+
+static time64_t get_32bit_time(const struct timestamp_expectation * const test)
+{
+	if (test->msb_set) {
+		if (test->lower_bound)
+			return LOWER_MSB_1;
+
+		return UPPER_MSB_1;
+	}
+
+	if (test->lower_bound)
+		return LOWER_MSB_0;
+	return UPPER_MSB_0;
+}
+
+
+/*
+ *  Test data is derived from the table in the Inode Timestamps section of
+ *  Documentation/filesystems/ext4/inodes.rst.
+ */
+static void inode_test_xtimestamp_decoding(struct kunit *test)
+{
+	struct timespec64 timestamp;
+
+	struct timestamp_expectation *test_param =
+			(struct timestamp_expectation *)(test->param_value);
+
+	timestamp = ext4_decode_extra_time(
+				cpu_to_le32(get_32bit_time(test_param)),
+				cpu_to_le32(test_param->extra_bits));
+
+	KUNIT_EXPECT_EQ_MSG(test,
+			    test_param->expected.tv_sec,
+			    timestamp.tv_sec,
+			    CASE_NAME_FORMAT,
+			    test_param->test_case_name,
+			    test_param->msb_set,
+			    test_param->lower_bound,
+			    test_param->extra_bits);
+	KUNIT_EXPECT_EQ_MSG(test,
+			    test_param->expected.tv_nsec,
+			    timestamp.tv_nsec,
+			    CASE_NAME_FORMAT,
+			    test_param->test_case_name,
+			    test_param->msb_set,
+			    test_param->lower_bound,
+			    test_param->extra_bits);
+}
+
+static struct kunit_case ext4_inode_test_cases[] = {
+	KUNIT_CASE_PARAM(inode_test_xtimestamp_decoding, ext4_inode_gen_params),
+	{}
+};
+
+static struct kunit_suite ext4_inode_test_suite = {
+	.name = "ext4_inode_test",
+	.test_cases = ext4_inode_test_cases,
+};
+
+kunit_test_suites(&ext4_inode_test_suite);
+
+MODULE_DESCRIPTION("KUnit test of ext4 inode timestamp decoding");
+MODULE_LICENSE("GPL v2");