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, 246 insertions, 0 deletions

diff --git a/fs/hfsplus/bitmap.c b/fs/hfsplus/bitmap.c
new file mode 100644
index 000000000..1b3af8c87
--- /dev/null
+++ b/fs/hfsplus/bitmap.c
@@ -0,0 +1,246 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/hfsplus/bitmap.c
+ *
+ * Copyright (C) 2001
+ * Brad Boyer (flar@allandria.com)
+ * (C) 2003 Ardis Technologies <roman@ardistech.com>
+ *
+ * Handling of allocation file
+ */
+
+#include <linux/pagemap.h>
+
+#include "hfsplus_fs.h"
+#include "hfsplus_raw.h"
+
+#define PAGE_CACHE_BITS	(PAGE_SIZE * 8)
+
+int hfsplus_block_allocate(struct super_block *sb, u32 size,
+		u32 offset, u32 *max)
+{
+	struct hfsplus_sb_info *sbi = HFSPLUS_SB(sb);
+	struct page *page;
+	struct address_space *mapping;
+	__be32 *pptr, *curr, *end;
+	u32 mask, start, len, n;
+	__be32 val;
+	int i;
+
+	len = *max;
+	if (!len)
+		return size;
+
+	hfs_dbg("size %u, offset %u, len %u\n", size, offset, len);
+	mutex_lock(&sbi->alloc_mutex);
+	mapping = sbi->alloc_file->i_mapping;
+	page = read_mapping_page(mapping, offset / PAGE_CACHE_BITS, NULL);
+	if (IS_ERR(page)) {
+		start = size;
+		goto out;
+	}
+	pptr = kmap_local_page(page);
+	curr = pptr + (offset & (PAGE_CACHE_BITS - 1)) / 32;
+	i = offset % 32;
+	offset &= ~(PAGE_CACHE_BITS - 1);
+	if ((size ^ offset) / PAGE_CACHE_BITS)
+		end = pptr + PAGE_CACHE_BITS / 32;
+	else
+		end = pptr + ((size + 31) & (PAGE_CACHE_BITS - 1)) / 32;
+
+	/* scan the first partial u32 for zero bits */
+	val = *curr;
+	if (~val) {
+		n = be32_to_cpu(val);
+		mask = (1U << 31) >> i;
+		for (; i < 32; mask >>= 1, i++) {
+			if (!(n & mask))
+				goto found;
+		}
+	}
+	curr++;
+
+	/* scan complete u32s for the first zero bit */
+	while (1) {
+		while (curr < end) {
+			val = *curr;
+			if (~val) {
+				n = be32_to_cpu(val);
+				mask = 1 << 31;
+				for (i = 0; i < 32; mask >>= 1, i++) {
+					if (!(n & mask))
+						goto found;
+				}
+			}
+			curr++;
+		}
+		kunmap_local(pptr);
+		offset += PAGE_CACHE_BITS;
+		if (offset >= size)
+			break;
+		page = read_mapping_page(mapping, offset / PAGE_CACHE_BITS,
+					 NULL);
+		if (IS_ERR(page)) {
+			start = size;
+			goto out;
+		}
+		curr = pptr = kmap_local_page(page);
+		if ((size ^ offset) / PAGE_CACHE_BITS)
+			end = pptr + PAGE_CACHE_BITS / 32;
+		else
+			end = pptr + ((size + 31) & (PAGE_CACHE_BITS - 1)) / 32;
+	}
+	hfs_dbg("bitmap full\n");
+	start = size;
+	goto out;
+
+found:
+	start = offset + (curr - pptr) * 32 + i;
+	if (start >= size) {
+		hfs_dbg("bitmap full\n");
+		goto out;
+	}
+	/* do any partial u32 at the start */
+	len = min(size - start, len);
+	while (1) {
+		n |= mask;
+		if (++i >= 32)
+			break;
+		mask >>= 1;
+		if (!--len || n & mask)
+			goto done;
+	}
+	if (!--len)
+		goto done;
+	*curr++ = cpu_to_be32(n);
+	/* do full u32s */
+	while (1) {
+		while (curr < end) {
+			n = be32_to_cpu(*curr);
+			if (len < 32)
+				goto last;
+			if (n) {
+				len = 32;
+				goto last;
+			}
+			*curr++ = cpu_to_be32(0xffffffff);
+			len -= 32;
+		}
+		set_page_dirty(page);
+		kunmap_local(pptr);
+		offset += PAGE_CACHE_BITS;
+		page = read_mapping_page(mapping, offset / PAGE_CACHE_BITS,
+					 NULL);
+		if (IS_ERR(page)) {
+			start = size;
+			goto out;
+		}
+		pptr = kmap_local_page(page);
+		curr = pptr;
+		end = pptr + PAGE_CACHE_BITS / 32;
+	}
+last:
+	/* do any partial u32 at end */
+	mask = 1U << 31;
+	for (i = 0; i < len; i++) {
+		if (n & mask)
+			break;
+		n |= mask;
+		mask >>= 1;
+	}
+done:
+	*curr = cpu_to_be32(n);
+	set_page_dirty(page);
+	kunmap_local(pptr);
+	*max = offset + (curr - pptr) * 32 + i - start;
+	sbi->free_blocks -= *max;
+	hfsplus_mark_mdb_dirty(sb);
+	hfs_dbg("start %u, max %u\n", start, *max);
+out:
+	mutex_unlock(&sbi->alloc_mutex);
+	return start;
+}
+
+int hfsplus_block_free(struct super_block *sb, u32 offset, u32 count)
+{
+	struct hfsplus_sb_info *sbi = HFSPLUS_SB(sb);
+	struct page *page;
+	struct address_space *mapping;
+	__be32 *pptr, *curr, *end;
+	u32 mask, len, pnr;
+	int i;
+
+	/* is there any actual work to be done? */
+	if (!count)
+		return 0;
+
+	hfs_dbg("offset %u, count %u\n", offset, count);
+	/* are all of the bits in range? */
+	if ((offset + count) > sbi->total_blocks)
+		return -ENOENT;
+
+	mutex_lock(&sbi->alloc_mutex);
+	mapping = sbi->alloc_file->i_mapping;
+	pnr = offset / PAGE_CACHE_BITS;
+	page = read_mapping_page(mapping, pnr, NULL);
+	if (IS_ERR(page))
+		goto kaboom;
+	pptr = kmap_local_page(page);
+	curr = pptr + (offset & (PAGE_CACHE_BITS - 1)) / 32;
+	end = pptr + PAGE_CACHE_BITS / 32;
+	len = count;
+
+	/* do any partial u32 at the start */
+	i = offset % 32;
+	if (i) {
+		int j = 32 - i;
+		mask = 0xffffffffU << j;
+		if (j > count) {
+			mask |= 0xffffffffU >> (i + count);
+			*curr++ &= cpu_to_be32(mask);
+			goto out;
+		}
+		*curr++ &= cpu_to_be32(mask);
+		count -= j;
+	}
+
+	/* do full u32s */
+	while (1) {
+		while (curr < end) {
+			if (count < 32)
+				goto done;
+			*curr++ = 0;
+			count -= 32;
+		}
+		if (!count)
+			break;
+		set_page_dirty(page);
+		kunmap_local(pptr);
+		page = read_mapping_page(mapping, ++pnr, NULL);
+		if (IS_ERR(page))
+			goto kaboom;
+		pptr = kmap_local_page(page);
+		curr = pptr;
+		end = pptr + PAGE_CACHE_BITS / 32;
+	}
+done:
+	/* do any partial u32 at end */
+	if (count) {
+		mask = 0xffffffffU >> count;
+		*curr &= cpu_to_be32(mask);
+	}
+out:
+	set_page_dirty(page);
+	kunmap_local(pptr);
+	sbi->free_blocks += len;
+	hfsplus_mark_mdb_dirty(sb);
+	mutex_unlock(&sbi->alloc_mutex);
+
+	return 0;
+
+kaboom:
+	pr_crit("unable to mark blocks free: error %ld\n", PTR_ERR(page));
+	mutex_unlock(&sbi->alloc_mutex);
+
+	return -EIO;
+}