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, 134 insertions, 0 deletions

diff --git a/fs/ntfs/lcnalloc.h b/fs/ntfs/lcnalloc.h
new file mode 100644
index 000000000..d9ac622e4
--- /dev/null
+++ b/fs/ntfs/lcnalloc.h
@@ -0,0 +1,134 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Exports for NTFS kernel cluster (de)allocation.
+ *
+ * Copyright (c) 2004-2005 Anton Altaparmakov
+ */
+
+#ifndef _LINUX_NTFS_LCNALLOC_H
+#define _LINUX_NTFS_LCNALLOC_H
+
+#include <linux/sched/mm.h>
+
+#include "attrib.h"
+
+/*
+ * enum zone_type - Zone identifiers for cluster allocation policy
+ *
+ * FIRST_ZONE		For sanity checking.
+ * MFT_ZONE		Allocate from $MFT zone.
+ * DATA_ZONE		Allocate from $DATA zone.
+ * LAST_ZONE		For sanity checking.
+ */
+enum {
+	FIRST_ZONE	= 0,
+	MFT_ZONE	= 0,
+	DATA_ZONE	= 1,
+	LAST_ZONE	= 1,
+};
+
+struct runlist_element *ntfs_cluster_alloc(struct ntfs_volume *vol,
+		const s64 start_vcn, const s64 count, const s64 start_lcn,
+		const int zone,
+		const bool is_extension,
+		const bool is_contig,
+		const bool is_dealloc);
+s64 __ntfs_cluster_free(struct ntfs_inode *ni, const s64 start_vcn,
+		s64 count, struct ntfs_attr_search_ctx *ctx, const bool is_rollback);
+
+/*
+ * ntfs_cluster_free - free clusters on an ntfs volume
+ * @ni:		ntfs inode whose runlist describes the clusters to free
+ * @start_vcn:	vcn in the runlist of @ni at which to start freeing clusters
+ * @count:	number of clusters to free or -1 for all clusters
+ * @ctx:	active attribute search context if present or NULL if not
+ *
+ * Free @count clusters starting at the cluster @start_vcn in the runlist
+ * described by the ntfs inode @ni.
+ *
+ * If @count is -1, all clusters from @start_vcn to the end of the runlist are
+ * deallocated.  Thus, to completely free all clusters in a runlist, use
+ * @start_vcn = 0 and @count = -1.
+ *
+ * If @ctx is specified, it is an active search context of @ni and its base mft
+ * record.  This is needed when ntfs_cluster_free() encounters unmapped runlist
+ * fragments and allows their mapping.  If you do not have the mft record
+ * mapped, you can specify @ctx as NULL and ntfs_cluster_free() will perform
+ * the necessary mapping and unmapping.
+ *
+ * Note, ntfs_cluster_free() saves the state of @ctx on entry and restores it
+ * before returning.  Thus, @ctx will be left pointing to the same attribute on
+ * return as on entry.  However, the actual pointers in @ctx may point to
+ * different memory locations on return, so you must remember to reset any
+ * cached pointers from the @ctx, i.e. after the call to ntfs_cluster_free(),
+ * you will probably want to do:
+ *	m = ctx->mrec;
+ *	a = ctx->attr;
+ * Assuming you cache ctx->attr in a variable @a of type ATTR_RECORD * and that
+ * you cache ctx->mrec in a variable @m of type MFT_RECORD *.
+ *
+ * Note, ntfs_cluster_free() does not modify the runlist, so you have to remove
+ * from the runlist or mark sparse the freed runs later.
+ *
+ * Return the number of deallocated clusters (not counting sparse ones) on
+ * success and -errno on error.
+ *
+ * WARNING: If @ctx is supplied, regardless of whether success or failure is
+ *	    returned, you need to check IS_ERR(@ctx->mrec) and if 'true' the @ctx
+ *	    is no longer valid, i.e. you need to either call
+ *	    ntfs_attr_reinit_search_ctx() or ntfs_attr_put_search_ctx() on it.
+ *	    In that case PTR_ERR(@ctx->mrec) will give you the error code for
+ *	    why the mapping of the old inode failed.
+ *
+ * Locking: - The runlist described by @ni must be locked for writing on entry
+ *	      and is locked on return.  Note the runlist may be modified when
+ *	      needed runlist fragments need to be mapped.
+ *	    - The volume lcn bitmap must be unlocked on entry and is unlocked
+ *	      on return.
+ *	    - This function takes the volume lcn bitmap lock for writing and
+ *	      modifies the bitmap contents.
+ *	    - If @ctx is NULL, the base mft record of @ni must not be mapped on
+ *	      entry and it will be left unmapped on return.
+ *	    - If @ctx is not NULL, the base mft record must be mapped on entry
+ *	      and it will be left mapped on return.
+ */
+static inline s64 ntfs_cluster_free(struct ntfs_inode *ni, const s64 start_vcn,
+		s64 count, struct ntfs_attr_search_ctx *ctx)
+{
+	return __ntfs_cluster_free(ni, start_vcn, count, ctx, false);
+}
+
+int ntfs_cluster_free_from_rl_nolock(struct ntfs_volume *vol,
+		const struct runlist_element *rl);
+
+/*
+ * ntfs_cluster_free_from_rl - free clusters from runlist
+ * @vol:	mounted ntfs volume on which to free the clusters
+ * @rl:		runlist describing the clusters to free
+ *
+ * Free all the clusters described by the runlist @rl on the volume @vol.  In
+ * the case of an error being returned, at least some of the clusters were not
+ * freed.
+ *
+ * Return 0 on success and -errno on error.
+ *
+ * Locking: - This function takes the volume lcn bitmap lock for writing and
+ *	      modifies the bitmap contents.
+ *	    - The caller must have locked the runlist @rl for reading or
+ *	      writing.
+ */
+static inline int ntfs_cluster_free_from_rl(struct ntfs_volume *vol,
+		const struct runlist_element *rl)
+{
+	int ret;
+	unsigned int memalloc_flags;
+
+	memalloc_flags = memalloc_nofs_save();
+	down_write(&vol->lcnbmp_lock);
+	ret = ntfs_cluster_free_from_rl_nolock(vol, rl);
+	up_write(&vol->lcnbmp_lock);
+	memalloc_nofs_restore(memalloc_flags);
+	return ret;
+}
+
+#endif /* defined _LINUX_NTFS_LCNALLOC_H */