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, 137 insertions, 0 deletions

diff --git a/fs/f2fs/hash.c b/fs/f2fs/hash.c
new file mode 100644
index 000000000..14082fe5e
--- /dev/null
+++ b/fs/f2fs/hash.c
@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/f2fs/hash.c
+ *
+ * Copyright (c) 2012 Samsung Electronics Co., Ltd.
+ *             http://www.samsung.com/
+ *
+ * Portions of this code from linux/fs/ext3/hash.c
+ *
+ * Copyright (C) 2002 by Theodore Ts'o
+ */
+#include <linux/types.h>
+#include <linux/fs.h>
+#include <linux/f2fs_fs.h>
+#include <linux/pagemap.h>
+#include <linux/unicode.h>
+
+#include "f2fs.h"
+
+/*
+ * Hashing code copied from ext3
+ */
+#define DELTA 0x9E3779B9
+
+static void TEA_transform(unsigned int buf[4], unsigned int const in[])
+{
+	__u32 sum = 0;
+	__u32 b0 = buf[0], b1 = buf[1];
+	__u32 a = in[0], b = in[1], c = in[2], d = in[3];
+	int n = 16;
+
+	do {
+		sum += DELTA;
+		b0 += ((b1 << 4)+a) ^ (b1+sum) ^ ((b1 >> 5)+b);
+		b1 += ((b0 << 4)+c) ^ (b0+sum) ^ ((b0 >> 5)+d);
+	} while (--n);
+
+	buf[0] += b0;
+	buf[1] += b1;
+}
+
+static void str2hashbuf(const unsigned char *msg, size_t len,
+				unsigned int *buf, int num)
+{
+	unsigned pad, val;
+	int i;
+
+	pad = (__u32)len | ((__u32)len << 8);
+	pad |= pad << 16;
+
+	val = pad;
+	if (len > num * 4)
+		len = num * 4;
+	for (i = 0; i < len; i++) {
+		if ((i % 4) == 0)
+			val = pad;
+		val = msg[i] + (val << 8);
+		if ((i % 4) == 3) {
+			*buf++ = val;
+			val = pad;
+			num--;
+		}
+	}
+	if (--num >= 0)
+		*buf++ = val;
+	while (--num >= 0)
+		*buf++ = pad;
+}
+
+static u32 TEA_hash_name(const u8 *p, size_t len)
+{
+	__u32 in[8], buf[4];
+
+	/* Initialize the default seed for the hash checksum functions */
+	buf[0] = 0x67452301;
+	buf[1] = 0xefcdab89;
+	buf[2] = 0x98badcfe;
+	buf[3] = 0x10325476;
+
+	while (1) {
+		str2hashbuf(p, len, in, 4);
+		TEA_transform(buf, in);
+		p += 16;
+		if (len <= 16)
+			break;
+		len -= 16;
+	}
+	return buf[0] & ~F2FS_HASH_COL_BIT;
+}
+
+/*
+ * Compute @fname->hash.  For all directories, @fname->disk_name must be set.
+ * For casefolded directories, @fname->usr_fname must be set, and also
+ * @fname->cf_name if the filename is valid Unicode and is not "." or "..".
+ */
+void f2fs_hash_filename(const struct inode *dir, struct f2fs_filename *fname)
+{
+	const u8 *name = fname->disk_name.name;
+	size_t len = fname->disk_name.len;
+
+	WARN_ON_ONCE(!name);
+
+	if (name_is_dot_dotdot(name, len)) {
+		fname->hash = 0;
+		return;
+	}
+
+#if IS_ENABLED(CONFIG_UNICODE)
+	if (IS_CASEFOLDED(dir)) {
+		/*
+		 * If the casefolded name is provided, hash it instead of the
+		 * on-disk name.  If the casefolded name is *not* provided, that
+		 * should only be because the name wasn't valid Unicode or was
+		 * "." or "..", so fall back to treating the name as an opaque
+		 * byte sequence.  Note that to handle encrypted directories,
+		 * the fallback must use usr_fname (plaintext) rather than
+		 * disk_name (ciphertext).
+		 */
+		WARN_ON_ONCE(!fname->usr_fname->name);
+		if (fname->cf_name.name) {
+			name = fname->cf_name.name;
+			len = fname->cf_name.len;
+		} else {
+			name = fname->usr_fname->name;
+			len = fname->usr_fname->len;
+		}
+		if (IS_ENCRYPTED(dir)) {
+			struct qstr tmp = QSTR_INIT(name, len);
+
+			fname->hash =
+				cpu_to_le32(fscrypt_fname_siphash(dir, &tmp));
+			return;
+		}
+	}
+#endif
+	fname->hash = cpu_to_le32(TEA_hash_name(name, len));
+}