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, 374 insertions, 0 deletions

diff --git a/fs/minix/itree_common.c b/fs/minix/itree_common.c
new file mode 100644
index 000000000..c3cd2c75a
--- /dev/null
+++ b/fs/minix/itree_common.c
@@ -0,0 +1,374 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Generic part */
+
+typedef struct {
+	block_t	*p;
+	block_t	key;
+	struct buffer_head *bh;
+} Indirect;
+
+static DEFINE_RWLOCK(pointers_lock);
+
+static inline void add_chain(Indirect *p, struct buffer_head *bh, block_t *v)
+{
+	p->key = *(p->p = v);
+	p->bh = bh;
+}
+
+static inline int verify_chain(Indirect *from, Indirect *to)
+{
+	while (from <= to && from->key == *from->p)
+		from++;
+	return (from > to);
+}
+
+static inline block_t *block_end(struct buffer_head *bh)
+{
+	return (block_t *)((char*)bh->b_data + bh->b_size);
+}
+
+static inline Indirect *get_branch(struct inode *inode,
+					int depth,
+					int *offsets,
+					Indirect chain[DEPTH],
+					int *err)
+{
+	struct super_block *sb = inode->i_sb;
+	Indirect *p = chain;
+	struct buffer_head *bh;
+
+	*err = 0;
+	/* i_data is not going away, no lock needed */
+	add_chain (chain, NULL, i_data(inode) + *offsets);
+	if (!p->key)
+		goto no_block;
+	while (--depth) {
+		bh = sb_bread(sb, block_to_cpu(p->key));
+		if (!bh)
+			goto failure;
+		read_lock(&pointers_lock);
+		if (!verify_chain(chain, p))
+			goto changed;
+		add_chain(++p, bh, (block_t *)bh->b_data + *++offsets);
+		read_unlock(&pointers_lock);
+		if (!p->key)
+			goto no_block;
+	}
+	return NULL;
+
+changed:
+	read_unlock(&pointers_lock);
+	brelse(bh);
+	*err = -EAGAIN;
+	goto no_block;
+failure:
+	*err = -EIO;
+no_block:
+	return p;
+}
+
+static int alloc_branch(struct inode *inode,
+			     int num,
+			     int *offsets,
+			     Indirect *branch)
+{
+	int n = 0;
+	int i;
+	int parent = minix_new_block(inode);
+	int err = -ENOSPC;
+
+	branch[0].key = cpu_to_block(parent);
+	if (parent) for (n = 1; n < num; n++) {
+		struct buffer_head *bh;
+		/* Allocate the next block */
+		int nr = minix_new_block(inode);
+		if (!nr)
+			break;
+		branch[n].key = cpu_to_block(nr);
+		bh = sb_getblk(inode->i_sb, parent);
+		if (!bh) {
+			minix_free_block(inode, nr);
+			err = -ENOMEM;
+			break;
+		}
+		lock_buffer(bh);
+		memset(bh->b_data, 0, bh->b_size);
+		branch[n].bh = bh;
+		branch[n].p = (block_t*) bh->b_data + offsets[n];
+		*branch[n].p = branch[n].key;
+		set_buffer_uptodate(bh);
+		unlock_buffer(bh);
+		mmb_mark_buffer_dirty(bh, &minix_i(inode)->i_metadata_bhs);
+		parent = nr;
+	}
+	if (n == num)
+		return 0;
+
+	/* Allocation failed, free what we already allocated */
+	for (i = 1; i < n; i++)
+		bforget(branch[i].bh);
+	for (i = 0; i < n; i++)
+		minix_free_block(inode, block_to_cpu(branch[i].key));
+	return err;
+}
+
+static inline int splice_branch(struct inode *inode,
+				     Indirect chain[DEPTH],
+				     Indirect *where,
+				     int num)
+{
+	int i;
+
+	write_lock(&pointers_lock);
+
+	/* Verify that place we are splicing to is still there and vacant */
+	if (!verify_chain(chain, where-1) || *where->p)
+		goto changed;
+
+	*where->p = where->key;
+
+	write_unlock(&pointers_lock);
+
+	/* We are done with atomic stuff, now do the rest of housekeeping */
+
+	inode_set_ctime_current(inode);
+
+	/* had we spliced it onto indirect block? */
+	if (where->bh)
+		mmb_mark_buffer_dirty(where->bh,
+				      &minix_i(inode)->i_metadata_bhs);
+
+	mark_inode_dirty(inode);
+	return 0;
+
+changed:
+	write_unlock(&pointers_lock);
+	for (i = 1; i < num; i++)
+		bforget(where[i].bh);
+	for (i = 0; i < num; i++)
+		minix_free_block(inode, block_to_cpu(where[i].key));
+	return -EAGAIN;
+}
+
+static int get_block(struct inode * inode, sector_t block,
+			struct buffer_head *bh, int create)
+{
+	int err = -EIO;
+	int offsets[DEPTH];
+	Indirect chain[DEPTH];
+	Indirect *partial;
+	int left;
+	int depth = block_to_path(inode, block, offsets);
+
+	if (depth == 0)
+		goto out;
+
+reread:
+	partial = get_branch(inode, depth, offsets, chain, &err);
+
+	/* Simplest case - block found, no allocation needed */
+	if (!partial) {
+got_it:
+		map_bh(bh, inode->i_sb, block_to_cpu(chain[depth-1].key));
+		/* Clean up and exit */
+		partial = chain+depth-1; /* the whole chain */
+		goto cleanup;
+	}
+
+	/* Next simple case - plain lookup or failed read of indirect block */
+	if (!create || err == -EIO) {
+cleanup:
+		while (partial > chain) {
+			brelse(partial->bh);
+			partial--;
+		}
+out:
+		return err;
+	}
+
+	/*
+	 * Indirect block might be removed by truncate while we were
+	 * reading it. Handling of that case (forget what we've got and
+	 * reread) is taken out of the main path.
+	 */
+	if (err == -EAGAIN)
+		goto changed;
+
+	left = (chain + depth) - partial;
+	err = alloc_branch(inode, left, offsets+(partial-chain), partial);
+	if (err)
+		goto cleanup;
+
+	if (splice_branch(inode, chain, partial, left) < 0)
+		goto changed;
+
+	set_buffer_new(bh);
+	goto got_it;
+
+changed:
+	while (partial > chain) {
+		brelse(partial->bh);
+		partial--;
+	}
+	goto reread;
+}
+
+static inline int all_zeroes(block_t *p, block_t *q)
+{
+	while (p < q)
+		if (*p++)
+			return 0;
+	return 1;
+}
+
+static Indirect *find_shared(struct inode *inode,
+				int depth,
+				int offsets[DEPTH],
+				Indirect chain[DEPTH],
+				block_t *top)
+{
+	Indirect *partial, *p;
+	int k, err;
+
+	*top = 0;
+	for (k = depth; k > 1 && !offsets[k-1]; k--)
+		;
+	partial = get_branch(inode, k, offsets, chain, &err);
+
+	write_lock(&pointers_lock);
+	if (!partial)
+		partial = chain + k-1;
+	if (!partial->key && *partial->p) {
+		write_unlock(&pointers_lock);
+		goto no_top;
+	}
+	for (p=partial;p>chain && all_zeroes((block_t*)p->bh->b_data,p->p);p--)
+		;
+	if (p == chain + k - 1 && p > chain) {
+		p->p--;
+	} else {
+		*top = *p->p;
+		*p->p = 0;
+	}
+	write_unlock(&pointers_lock);
+
+	while(partial > p)
+	{
+		brelse(partial->bh);
+		partial--;
+	}
+no_top:
+	return partial;
+}
+
+static inline void free_data(struct inode *inode, block_t *p, block_t *q)
+{
+	unsigned long nr;
+
+	for ( ; p < q ; p++) {
+		nr = block_to_cpu(*p);
+		if (nr) {
+			*p = 0;
+			minix_free_block(inode, nr);
+		}
+	}
+}
+
+static void free_branches(struct inode *inode, block_t *p, block_t *q, int depth)
+{
+	struct buffer_head * bh;
+	unsigned long nr;
+
+	if (depth--) {
+		for ( ; p < q ; p++) {
+			nr = block_to_cpu(*p);
+			if (!nr)
+				continue;
+			*p = 0;
+			bh = sb_bread(inode->i_sb, nr);
+			if (!bh)
+				continue;
+			free_branches(inode, (block_t*)bh->b_data,
+				      block_end(bh), depth);
+			bforget(bh);
+			minix_free_block(inode, nr);
+			mark_inode_dirty(inode);
+		}
+	} else
+		free_data(inode, p, q);
+}
+
+static inline void truncate (struct inode * inode)
+{
+	struct super_block *sb = inode->i_sb;
+	block_t *idata = i_data(inode);
+	int offsets[DEPTH];
+	Indirect chain[DEPTH];
+	Indirect *partial;
+	block_t nr = 0;
+	int n;
+	int first_whole;
+	long iblock;
+
+	iblock = (inode->i_size + sb->s_blocksize -1) >> sb->s_blocksize_bits;
+	block_truncate_page(inode->i_mapping, inode->i_size, get_block);
+
+	n = block_to_path(inode, iblock, offsets);
+	if (!n)
+		return;
+
+	if (n == 1) {
+		free_data(inode, idata+offsets[0], idata + DIRECT);
+		first_whole = 0;
+		goto do_indirects;
+	}
+
+	first_whole = offsets[0] + 1 - DIRECT;
+	partial = find_shared(inode, n, offsets, chain, &nr);
+	if (nr) {
+		if (partial == chain)
+			mark_inode_dirty(inode);
+		else
+			mmb_mark_buffer_dirty(partial->bh,
+					      &minix_i(inode)->i_metadata_bhs);
+		free_branches(inode, &nr, &nr+1, (chain+n-1) - partial);
+	}
+	/* Clear the ends of indirect blocks on the shared branch */
+	while (partial > chain) {
+		free_branches(inode, partial->p + 1, block_end(partial->bh),
+				(chain+n-1) - partial);
+		mmb_mark_buffer_dirty(partial->bh,
+				      &minix_i(inode)->i_metadata_bhs);
+		brelse (partial->bh);
+		partial--;
+	}
+do_indirects:
+	/* Kill the remaining (whole) subtrees */
+	while (first_whole < DEPTH-1) {
+		nr = idata[DIRECT+first_whole];
+		if (nr) {
+			idata[DIRECT+first_whole] = 0;
+			mark_inode_dirty(inode);
+			free_branches(inode, &nr, &nr+1, first_whole+1);
+		}
+		first_whole++;
+	}
+	inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
+	mark_inode_dirty(inode);
+}
+
+static inline unsigned nblocks(loff_t size, struct super_block *sb)
+{
+	int k = sb->s_blocksize_bits - 10;
+	unsigned blocks, res, direct = DIRECT, i = DEPTH;
+	blocks = (size + sb->s_blocksize - 1) >> (BLOCK_SIZE_BITS + k);
+	res = blocks;
+	while (--i && blocks > direct) {
+		blocks -= direct;
+		blocks += sb->s_blocksize/sizeof(block_t) - 1;
+		blocks /= sb->s_blocksize/sizeof(block_t);
+		res += blocks;
+		direct = 1;
+	}
+	return res;
+}