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, 269 insertions, 0 deletions

diff --git a/fs/minix/bitmap.c b/fs/minix/bitmap.c
new file mode 100644
index 000000000..abec43833
--- /dev/null
+++ b/fs/minix/bitmap.c
@@ -0,0 +1,269 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/minix/bitmap.c
+ *
+ *  Copyright (C) 1991, 1992  Linus Torvalds
+ */
+
+/*
+ * Modified for 680x0 by Hamish Macdonald
+ * Fixed for 680x0 by Andreas Schwab
+ */
+
+/* bitmap.c contains the code that handles the inode and block bitmaps */
+
+#include "minix.h"
+#include <linux/buffer_head.h>
+#include <linux/bitops.h>
+#include <linux/sched.h>
+
+static DEFINE_SPINLOCK(bitmap_lock);
+
+/*
+ * bitmap consists of blocks filled with 16bit words
+ * bit set == busy, bit clear == free
+ * endianness is a mess, but for counting zero bits it really doesn't matter...
+ */
+static __u32 count_free(struct buffer_head *map[], unsigned blocksize, __u32 numbits)
+{
+	__u32 sum = 0;
+	unsigned blocks = DIV_ROUND_UP(numbits, blocksize * 8);
+
+	while (blocks--) {
+		unsigned words = blocksize / 2;
+		__u16 *p = (__u16 *)(*map++)->b_data;
+		while (words--)
+			sum += 16 - hweight16(*p++);
+	}
+
+	return sum;
+}
+
+void minix_free_block(struct inode *inode, unsigned long block)
+{
+	struct super_block *sb = inode->i_sb;
+	struct minix_sb_info *sbi = minix_sb(sb);
+	struct buffer_head *bh;
+	int k = sb->s_blocksize_bits + 3;
+	unsigned long bit, zone;
+
+	if (block < sbi->s_firstdatazone || block >= sbi->s_nzones) {
+		printk("Trying to free block not in datazone\n");
+		return;
+	}
+	zone = block - sbi->s_firstdatazone + 1;
+	bit = zone & ((1<<k) - 1);
+	zone >>= k;
+	if (zone >= sbi->s_zmap_blocks) {
+		printk("minix_free_block: nonexistent bitmap buffer\n");
+		return;
+	}
+	bh = sbi->s_zmap[zone];
+	spin_lock(&bitmap_lock);
+	if (!minix_test_and_clear_bit(bit, bh->b_data))
+		printk("minix_free_block (%s:%lu): bit already cleared\n",
+		       sb->s_id, block);
+	spin_unlock(&bitmap_lock);
+	mark_buffer_dirty(bh);
+	return;
+}
+
+int minix_new_block(struct inode * inode)
+{
+	struct minix_sb_info *sbi = minix_sb(inode->i_sb);
+	int bits_per_zone = 8 * inode->i_sb->s_blocksize;
+	int i;
+
+	for (i = 0; i < sbi->s_zmap_blocks; i++) {
+		struct buffer_head *bh = sbi->s_zmap[i];
+		int j;
+
+		spin_lock(&bitmap_lock);
+		j = minix_find_first_zero_bit(bh->b_data, bits_per_zone);
+		if (j < bits_per_zone) {
+			minix_set_bit(j, bh->b_data);
+			spin_unlock(&bitmap_lock);
+			mark_buffer_dirty(bh);
+			j += i * bits_per_zone + sbi->s_firstdatazone-1;
+			if (j < sbi->s_firstdatazone || j >= sbi->s_nzones)
+				break;
+			return j;
+		}
+		spin_unlock(&bitmap_lock);
+	}
+	return 0;
+}
+
+unsigned long minix_count_free_blocks(struct super_block *sb)
+{
+	struct minix_sb_info *sbi = minix_sb(sb);
+	u32 bits = sbi->s_nzones - sbi->s_firstdatazone + 1;
+
+	return (count_free(sbi->s_zmap, sb->s_blocksize, bits)
+		<< sbi->s_log_zone_size);
+}
+
+struct minix_inode *
+minix_V1_raw_inode(struct super_block *sb, ino_t ino, struct buffer_head **bh)
+{
+	int block;
+	struct minix_sb_info *sbi = minix_sb(sb);
+	struct minix_inode *p;
+
+	if (!ino || ino > sbi->s_ninodes) {
+		printk("Bad inode number on dev %s: %ld is out of range\n",
+		       sb->s_id, (long)ino);
+		return NULL;
+	}
+	ino--;
+	block = 2 + sbi->s_imap_blocks + sbi->s_zmap_blocks +
+		 ino / MINIX_INODES_PER_BLOCK;
+	*bh = sb_bread(sb, block);
+	if (!*bh) {
+		printk("Unable to read inode block\n");
+		return NULL;
+	}
+	p = (void *)(*bh)->b_data;
+	return p + ino % MINIX_INODES_PER_BLOCK;
+}
+
+struct minix2_inode *
+minix_V2_raw_inode(struct super_block *sb, ino_t ino, struct buffer_head **bh)
+{
+	int block;
+	struct minix_sb_info *sbi = minix_sb(sb);
+	struct minix2_inode *p;
+	int minix2_inodes_per_block = sb->s_blocksize / sizeof(struct minix2_inode);
+
+	*bh = NULL;
+	if (!ino || ino > sbi->s_ninodes) {
+		printk("Bad inode number on dev %s: %ld is out of range\n",
+		       sb->s_id, (long)ino);
+		return NULL;
+	}
+	ino--;
+	block = 2 + sbi->s_imap_blocks + sbi->s_zmap_blocks +
+		 ino / minix2_inodes_per_block;
+	*bh = sb_bread(sb, block);
+	if (!*bh) {
+		printk("Unable to read inode block\n");
+		return NULL;
+	}
+	p = (void *)(*bh)->b_data;
+	return p + ino % minix2_inodes_per_block;
+}
+
+/* Clear the link count and mode of a deleted inode on disk. */
+
+static void minix_clear_inode(struct inode *inode)
+{
+	struct buffer_head *bh = NULL;
+
+	if (INODE_VERSION(inode) == MINIX_V1) {
+		struct minix_inode *raw_inode;
+		raw_inode = minix_V1_raw_inode(inode->i_sb, inode->i_ino, &bh);
+		if (raw_inode) {
+			raw_inode->i_nlinks = 0;
+			raw_inode->i_mode = 0;
+		}
+	} else {
+		struct minix2_inode *raw_inode;
+		raw_inode = minix_V2_raw_inode(inode->i_sb, inode->i_ino, &bh);
+		if (raw_inode) {
+			raw_inode->i_nlinks = 0;
+			raw_inode->i_mode = 0;
+		}
+	}
+	if (bh) {
+		mark_buffer_dirty(bh);
+		brelse (bh);
+	}
+}
+
+void minix_free_inode(struct inode * inode)
+{
+	struct super_block *sb = inode->i_sb;
+	struct minix_sb_info *sbi = minix_sb(inode->i_sb);
+	struct buffer_head *bh;
+	int k = sb->s_blocksize_bits + 3;
+	unsigned long ino, bit;
+
+	ino = inode->i_ino;
+	if (ino < 1 || ino > sbi->s_ninodes) {
+		printk("minix_free_inode: inode 0 or nonexistent inode\n");
+		return;
+	}
+	bit = ino & ((1<<k) - 1);
+	ino >>= k;
+	if (ino >= sbi->s_imap_blocks) {
+		printk("minix_free_inode: nonexistent imap in superblock\n");
+		return;
+	}
+
+	minix_clear_inode(inode);	/* clear on-disk copy */
+
+	bh = sbi->s_imap[ino];
+	spin_lock(&bitmap_lock);
+	if (!minix_test_and_clear_bit(bit, bh->b_data))
+		printk("minix_free_inode: bit %lu already cleared\n", bit);
+	spin_unlock(&bitmap_lock);
+	mark_buffer_dirty(bh);
+}
+
+struct inode *minix_new_inode(const struct inode *dir, umode_t mode)
+{
+	struct super_block *sb = dir->i_sb;
+	struct minix_sb_info *sbi = minix_sb(sb);
+	struct inode *inode = new_inode(sb);
+	struct buffer_head * bh;
+	int bits_per_zone = 8 * sb->s_blocksize;
+	unsigned long j;
+	int i;
+
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+	j = bits_per_zone;
+	bh = NULL;
+	spin_lock(&bitmap_lock);
+	for (i = 0; i < sbi->s_imap_blocks; i++) {
+		bh = sbi->s_imap[i];
+		j = minix_find_first_zero_bit(bh->b_data, bits_per_zone);
+		if (j < bits_per_zone)
+			break;
+	}
+	if (!bh || j >= bits_per_zone) {
+		spin_unlock(&bitmap_lock);
+		iput(inode);
+		return ERR_PTR(-ENOSPC);
+	}
+	if (minix_test_and_set_bit(j, bh->b_data)) {	/* shouldn't happen */
+		spin_unlock(&bitmap_lock);
+		printk("minix_new_inode: bit already set\n");
+		iput(inode);
+		return ERR_PTR(-ENOSPC);
+	}
+	spin_unlock(&bitmap_lock);
+	mark_buffer_dirty(bh);
+	j += i * bits_per_zone;
+	if (!j || j > sbi->s_ninodes) {
+		iput(inode);
+		return ERR_PTR(-EFSCORRUPTED);
+	}
+	inode_init_owner(&nop_mnt_idmap, inode, dir, mode);
+	inode->i_ino = j;
+	simple_inode_init_ts(inode);
+	inode->i_blocks = 0;
+	memset(&minix_i(inode)->u, 0, sizeof(minix_i(inode)->u));
+	insert_inode_hash(inode);
+	mark_inode_dirty(inode);
+
+	return inode;
+}
+
+unsigned long minix_count_free_inodes(struct super_block *sb)
+{
+	struct minix_sb_info *sbi = minix_sb(sb);
+	u32 bits = sbi->s_ninodes + 1;
+
+	return count_free(sbi->s_imap, sb->s_blocksize, bits);
+}