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, 347 insertions, 0 deletions

diff --git a/fs/ext4/hash.c b/fs/ext4/hash.c
new file mode 100644
index 000000000..978bd92da
--- /dev/null
+++ b/fs/ext4/hash.c
@@ -0,0 +1,347 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/ext4/hash.c
+ *
+ * Copyright (C) 2002 by Theodore Ts'o
+ */
+
+#include <linux/fs.h>
+#include <linux/unicode.h>
+#include <linux/compiler.h>
+#include <linux/bitops.h>
+#include <linux/unaligned.h>
+#include "ext4.h"
+
+#define DELTA 0x9E3779B9
+
+static void TEA_transform(__u32 buf[4], __u32 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;
+}
+
+/* F, G and H are basic MD4 functions: selection, majority, parity */
+#define F(x, y, z) ((z) ^ ((x) & ((y) ^ (z))))
+#define G(x, y, z) (((x) & (y)) + (((x) ^ (y)) & (z)))
+#define H(x, y, z) ((x) ^ (y) ^ (z))
+
+/*
+ * The generic round function.  The application is so specific that
+ * we don't bother protecting all the arguments with parens, as is generally
+ * good macro practice, in favor of extra legibility.
+ * Rotation is separate from addition to prevent recomputation
+ */
+#define ROUND(f, a, b, c, d, x, s)	\
+	(a += f(b, c, d) + x, a = rol32(a, s))
+#define K1 0
+#define K2 013240474631UL
+#define K3 015666365641UL
+
+/*
+ * Basic cut-down MD4 transform.  Returns only 32 bits of result.
+ */
+static __u32 half_md4_transform(__u32 buf[4], __u32 const in[8])
+{
+	__u32 a = buf[0], b = buf[1], c = buf[2], d = buf[3];
+
+	/* Round 1 */
+	ROUND(F, a, b, c, d, in[0] + K1,  3);
+	ROUND(F, d, a, b, c, in[1] + K1,  7);
+	ROUND(F, c, d, a, b, in[2] + K1, 11);
+	ROUND(F, b, c, d, a, in[3] + K1, 19);
+	ROUND(F, a, b, c, d, in[4] + K1,  3);
+	ROUND(F, d, a, b, c, in[5] + K1,  7);
+	ROUND(F, c, d, a, b, in[6] + K1, 11);
+	ROUND(F, b, c, d, a, in[7] + K1, 19);
+
+	/* Round 2 */
+	ROUND(G, a, b, c, d, in[1] + K2,  3);
+	ROUND(G, d, a, b, c, in[3] + K2,  5);
+	ROUND(G, c, d, a, b, in[5] + K2,  9);
+	ROUND(G, b, c, d, a, in[7] + K2, 13);
+	ROUND(G, a, b, c, d, in[0] + K2,  3);
+	ROUND(G, d, a, b, c, in[2] + K2,  5);
+	ROUND(G, c, d, a, b, in[4] + K2,  9);
+	ROUND(G, b, c, d, a, in[6] + K2, 13);
+
+	/* Round 3 */
+	ROUND(H, a, b, c, d, in[3] + K3,  3);
+	ROUND(H, d, a, b, c, in[7] + K3,  9);
+	ROUND(H, c, d, a, b, in[2] + K3, 11);
+	ROUND(H, b, c, d, a, in[6] + K3, 15);
+	ROUND(H, a, b, c, d, in[1] + K3,  3);
+	ROUND(H, d, a, b, c, in[5] + K3,  9);
+	ROUND(H, c, d, a, b, in[0] + K3, 11);
+	ROUND(H, b, c, d, a, in[4] + K3, 15);
+
+	buf[0] += a;
+	buf[1] += b;
+	buf[2] += c;
+	buf[3] += d;
+
+	return buf[1]; /* "most hashed" word */
+}
+#undef ROUND
+#undef K1
+#undef K2
+#undef K3
+#undef F
+#undef G
+#undef H
+
+/* The old legacy hash */
+static __u32 dx_hack_hash_unsigned(const char *name, int len)
+{
+	__u32 hash, hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
+	const unsigned char *ucp = (const unsigned char *) name;
+
+	while (len--) {
+		hash = hash1 + (hash0 ^ (((int) *ucp++) * 7152373));
+
+		if (hash & 0x80000000)
+			hash -= 0x7fffffff;
+		hash1 = hash0;
+		hash0 = hash;
+	}
+	return hash0 << 1;
+}
+
+static __u32 dx_hack_hash_signed(const char *name, int len)
+{
+	__u32 hash, hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
+	const signed char *scp = (const signed char *) name;
+
+	while (len--) {
+		hash = hash1 + (hash0 ^ (((int) *scp++) * 7152373));
+
+		if (hash & 0x80000000)
+			hash -= 0x7fffffff;
+		hash1 = hash0;
+		hash0 = hash;
+	}
+	return hash0 << 1;
+}
+
+static void str2hashbuf_signed(const char *msg, int len, __u32 *buf, int num)
+{
+	__u32	pad, val;
+	int	i;
+	const signed char *scp = (const signed char *) msg;
+
+	pad = (__u32)len | ((__u32)len << 8);
+	pad |= pad << 16;
+
+	if (len > num*4)
+		len = num * 4;
+
+	while (len >= 4) {
+		val = ((__u32)scp[0] << 24) + ((__u32)scp[1] << 16) + ((__u32)scp[2] << 8) + scp[3];
+		*buf++ = val;
+		scp += 4;
+		len -= 4;
+		num--;
+	}
+
+	val = pad;
+
+	for (i = 0; i < len; i++)
+		val = scp[i] + (val << 8);
+
+	if (--num >= 0)
+		*buf++ = val;
+
+	while (--num >= 0)
+		*buf++ = pad;
+
+}
+
+static void str2hashbuf_unsigned(const char *msg, int len, __u32 *buf, int num)
+{
+	__u32	pad, val;
+	int	i;
+	const unsigned char *ucp = (const unsigned char *) msg;
+
+	pad = (__u32)len | ((__u32)len << 8);
+	pad |= pad << 16;
+
+	if (len > num*4)
+		len = num * 4;
+
+	while (len >= 4) {
+		val = get_unaligned_be32(ucp);
+		*buf++ = val;
+		ucp += 4;
+		len -= 4;
+		num--;
+	}
+
+	val = pad;
+
+	for (i = 0; i < len; i++)
+		val = ucp[i] + (val << 8);
+
+	if (--num >= 0)
+		*buf++ = val;
+
+	while (--num >= 0)
+		*buf++ = pad;
+
+}
+
+/*
+ * Returns the hash of a filename.  If len is 0 and name is NULL, then
+ * this function can be used to test whether or not a hash version is
+ * supported.
+ *
+ * The seed is an 4 longword (32 bits) "secret" which can be used to
+ * uniquify a hash.  If the seed is all zero's, then some default seed
+ * may be used.
+ *
+ * A particular hash version specifies whether or not the seed is
+ * represented, and whether or not the returned hash is 32 bits or 64
+ * bits.  32 bit hashes will return 0 for the minor hash.
+ */
+static int __ext4fs_dirhash(const struct inode *dir, const char *name, int len,
+			    struct dx_hash_info *hinfo)
+{
+	__u32	hash;
+	__u32	minor_hash = 0;
+	const char	*p;
+	int		i;
+	__u32		in[8], buf[4];
+	bool use_unsigned = false;
+
+	/* Initialize the default seed for the hash checksum functions */
+	buf[0] = 0x67452301;
+	buf[1] = 0xefcdab89;
+	buf[2] = 0x98badcfe;
+	buf[3] = 0x10325476;
+
+	/* Check to see if the seed is all zero's */
+	if (hinfo->seed) {
+		for (i = 0; i < 4; i++) {
+			if (hinfo->seed[i]) {
+				memcpy(buf, hinfo->seed, sizeof(buf));
+				break;
+			}
+		}
+	}
+
+	switch (hinfo->hash_version) {
+	case DX_HASH_LEGACY_UNSIGNED:
+		hash = dx_hack_hash_unsigned(name, len);
+		break;
+	case DX_HASH_LEGACY:
+		hash = dx_hack_hash_signed(name, len);
+		break;
+	case DX_HASH_HALF_MD4_UNSIGNED:
+		use_unsigned = true;
+		fallthrough;
+	case DX_HASH_HALF_MD4:
+		p = name;
+		while (len > 0) {
+			if (use_unsigned)
+				str2hashbuf_unsigned(p, len, in, 8);
+			else
+				str2hashbuf_signed(p, len, in, 8);
+			half_md4_transform(buf, in);
+			len -= 32;
+			p += 32;
+		}
+		minor_hash = buf[2];
+		hash = buf[1];
+		break;
+	case DX_HASH_TEA_UNSIGNED:
+		use_unsigned = true;
+		fallthrough;
+	case DX_HASH_TEA:
+		p = name;
+		while (len > 0) {
+			if (use_unsigned)
+				str2hashbuf_unsigned(p, len, in, 4);
+			else
+				str2hashbuf_signed(p, len, in, 4);
+			TEA_transform(buf, in);
+			len -= 16;
+			p += 16;
+		}
+		hash = buf[0];
+		minor_hash = buf[1];
+		break;
+	case DX_HASH_SIPHASH:
+	{
+		struct qstr qname = QSTR_INIT(name, len);
+		__u64	combined_hash;
+
+		if (fscrypt_has_encryption_key(dir)) {
+			combined_hash = fscrypt_fname_siphash(dir, &qname);
+		} else {
+			ext4_warning_inode(dir, "Siphash requires key");
+			return -EINVAL;
+		}
+
+		hash = (__u32)(combined_hash >> 32);
+		minor_hash = (__u32)combined_hash;
+		break;
+	}
+	default:
+		hinfo->hash = 0;
+		hinfo->minor_hash = 0;
+		ext4_warning(dir->i_sb,
+			     "invalid/unsupported hash tree version %u",
+			     hinfo->hash_version);
+		return -EINVAL;
+	}
+	hash = hash & ~1;
+	if (hash == (EXT4_HTREE_EOF_32BIT << 1))
+		hash = (EXT4_HTREE_EOF_32BIT - 1) << 1;
+	hinfo->hash = hash;
+	hinfo->minor_hash = minor_hash;
+	return 0;
+}
+
+int ext4fs_dirhash(const struct inode *dir, const char *name, int len,
+		   struct dx_hash_info *hinfo)
+{
+#if IS_ENABLED(CONFIG_UNICODE)
+	const struct unicode_map *um = dir->i_sb->s_encoding;
+	int r, dlen;
+	unsigned char *buff;
+	struct qstr qstr = {.name = name, .len = len };
+
+	if (len && IS_CASEFOLDED(dir) &&
+	   (!IS_ENCRYPTED(dir) || fscrypt_has_encryption_key(dir))) {
+		buff = kzalloc(PATH_MAX, GFP_KERNEL);
+		if (!buff)
+			return -ENOMEM;
+
+		dlen = utf8_casefold(um, &qstr, buff, PATH_MAX);
+		if (dlen < 0) {
+			kfree(buff);
+			goto opaque_seq;
+		}
+
+		r = __ext4fs_dirhash(dir, buff, dlen, hinfo);
+
+		kfree(buff);
+		return r;
+	}
+opaque_seq:
+#endif
+	return __ext4fs_dirhash(dir, name, len, hinfo);
+}
+
+#if IS_ENABLED(CONFIG_EXT4_KUNIT_TESTS)
+EXPORT_SYMBOL_FOR_EXT4_TEST(ext4fs_dirhash);
+#endif