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, 299 insertions, 0 deletions

diff --git a/fs/jffs2/malloc.c b/fs/jffs2/malloc.c
new file mode 100644
index 000000000..411de8b36
--- /dev/null
+++ b/fs/jffs2/malloc.c
@@ -0,0 +1,299 @@
+/*
+ * JFFS2 -- Journalling Flash File System, Version 2.
+ *
+ * Copyright © 2001-2007 Red Hat, Inc.
+ *
+ * Created by David Woodhouse <dwmw2@infradead.org>
+ *
+ * For licensing information, see the file 'LICENCE' in this directory.
+ *
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/jffs2.h>
+#include "nodelist.h"
+
+/* These are initialised to NULL in the kernel startup code.
+   If you're porting to other operating systems, beware */
+static struct kmem_cache *full_dnode_slab;
+static struct kmem_cache *raw_dirent_slab;
+static struct kmem_cache *raw_inode_slab;
+static struct kmem_cache *tmp_dnode_info_slab;
+static struct kmem_cache *raw_node_ref_slab;
+static struct kmem_cache *node_frag_slab;
+static struct kmem_cache *inode_cache_slab;
+#ifdef CONFIG_JFFS2_FS_XATTR
+static struct kmem_cache *xattr_datum_cache;
+static struct kmem_cache *xattr_ref_cache;
+#endif
+
+int __init jffs2_create_slab_caches(void)
+{
+	full_dnode_slab = KMEM_CACHE(jffs2_full_dnode, 0);
+	if (!full_dnode_slab)
+		goto err;
+
+	raw_dirent_slab = KMEM_CACHE(jffs2_raw_dirent, SLAB_HWCACHE_ALIGN);
+	if (!raw_dirent_slab)
+		goto err;
+
+	raw_inode_slab = KMEM_CACHE(jffs2_raw_inode, SLAB_HWCACHE_ALIGN);
+	if (!raw_inode_slab)
+		goto err;
+
+	tmp_dnode_info_slab = KMEM_CACHE(jffs2_tmp_dnode_info, 0);
+	if (!tmp_dnode_info_slab)
+		goto err;
+
+	raw_node_ref_slab = kmem_cache_create("jffs2_refblock",
+					      sizeof(struct jffs2_raw_node_ref) * (REFS_PER_BLOCK + 1),
+					      0, 0, NULL);
+	if (!raw_node_ref_slab)
+		goto err;
+
+	node_frag_slab = KMEM_CACHE(jffs2_node_frag, 0);
+	if (!node_frag_slab)
+		goto err;
+
+	inode_cache_slab = KMEM_CACHE(jffs2_inode_cache, 0);
+	if (!inode_cache_slab)
+		goto err;
+
+#ifdef CONFIG_JFFS2_FS_XATTR
+	xattr_datum_cache = KMEM_CACHE(jffs2_xattr_datum, 0);
+	if (!xattr_datum_cache)
+		goto err;
+
+	xattr_ref_cache = KMEM_CACHE(jffs2_xattr_ref, 0);
+	if (!xattr_ref_cache)
+		goto err;
+#endif
+
+	return 0;
+ err:
+	jffs2_destroy_slab_caches();
+	return -ENOMEM;
+}
+
+void jffs2_destroy_slab_caches(void)
+{
+	kmem_cache_destroy(full_dnode_slab);
+	kmem_cache_destroy(raw_dirent_slab);
+	kmem_cache_destroy(raw_inode_slab);
+	kmem_cache_destroy(tmp_dnode_info_slab);
+	kmem_cache_destroy(raw_node_ref_slab);
+	kmem_cache_destroy(node_frag_slab);
+	kmem_cache_destroy(inode_cache_slab);
+#ifdef CONFIG_JFFS2_FS_XATTR
+	kmem_cache_destroy(xattr_datum_cache);
+	kmem_cache_destroy(xattr_ref_cache);
+#endif
+}
+
+struct jffs2_full_dirent *jffs2_alloc_full_dirent(int namesize)
+{
+	struct jffs2_full_dirent *ret;
+	ret = kmalloc(sizeof(struct jffs2_full_dirent) + namesize, GFP_KERNEL);
+	dbg_memalloc("%p\n", ret);
+	return ret;
+}
+
+void jffs2_free_full_dirent(struct jffs2_full_dirent *x)
+{
+	dbg_memalloc("%p\n", x);
+	kfree(x);
+}
+
+struct jffs2_full_dnode *jffs2_alloc_full_dnode(void)
+{
+	struct jffs2_full_dnode *ret;
+	ret = kmem_cache_alloc(full_dnode_slab, GFP_KERNEL);
+	dbg_memalloc("%p\n", ret);
+	return ret;
+}
+
+void jffs2_free_full_dnode(struct jffs2_full_dnode *x)
+{
+	dbg_memalloc("%p\n", x);
+	kmem_cache_free(full_dnode_slab, x);
+}
+
+struct jffs2_raw_dirent *jffs2_alloc_raw_dirent(void)
+{
+	struct jffs2_raw_dirent *ret;
+	ret = kmem_cache_alloc(raw_dirent_slab, GFP_KERNEL);
+	dbg_memalloc("%p\n", ret);
+	return ret;
+}
+
+void jffs2_free_raw_dirent(struct jffs2_raw_dirent *x)
+{
+	dbg_memalloc("%p\n", x);
+	kmem_cache_free(raw_dirent_slab, x);
+}
+
+struct jffs2_raw_inode *jffs2_alloc_raw_inode(void)
+{
+	struct jffs2_raw_inode *ret;
+	ret = kmem_cache_alloc(raw_inode_slab, GFP_KERNEL);
+	dbg_memalloc("%p\n", ret);
+	return ret;
+}
+
+void jffs2_free_raw_inode(struct jffs2_raw_inode *x)
+{
+	dbg_memalloc("%p\n", x);
+	kmem_cache_free(raw_inode_slab, x);
+}
+
+struct jffs2_tmp_dnode_info *jffs2_alloc_tmp_dnode_info(void)
+{
+	struct jffs2_tmp_dnode_info *ret;
+	ret = kmem_cache_alloc(tmp_dnode_info_slab, GFP_KERNEL);
+	dbg_memalloc("%p\n",
+		ret);
+	return ret;
+}
+
+void jffs2_free_tmp_dnode_info(struct jffs2_tmp_dnode_info *x)
+{
+	dbg_memalloc("%p\n", x);
+	kmem_cache_free(tmp_dnode_info_slab, x);
+}
+
+static struct jffs2_raw_node_ref *jffs2_alloc_refblock(void)
+{
+	struct jffs2_raw_node_ref *ret;
+
+	ret = kmem_cache_alloc(raw_node_ref_slab, GFP_KERNEL);
+	if (ret) {
+		int i = 0;
+		for (i=0; i < REFS_PER_BLOCK; i++) {
+			ret[i].flash_offset = REF_EMPTY_NODE;
+			ret[i].next_in_ino = NULL;
+		}
+		ret[i].flash_offset = REF_LINK_NODE;
+		ret[i].next_in_ino = NULL;
+	}
+	return ret;
+}
+
+int jffs2_prealloc_raw_node_refs(struct jffs2_sb_info *c,
+				 struct jffs2_eraseblock *jeb, int nr)
+{
+	struct jffs2_raw_node_ref **p, *ref;
+	int i = nr;
+
+	dbg_memalloc("%d\n", nr);
+
+	p = &jeb->last_node;
+	ref = *p;
+
+	dbg_memalloc("Reserving %d refs for block @0x%08x\n", nr, jeb->offset);
+
+	/* If jeb->last_node is really a valid node then skip over it */
+	if (ref && ref->flash_offset != REF_EMPTY_NODE)
+		ref++;
+
+	while (i) {
+		if (!ref) {
+			dbg_memalloc("Allocating new refblock linked from %p\n", p);
+			ref = *p = jffs2_alloc_refblock();
+			if (!ref)
+				return -ENOMEM;
+		}
+		if (ref->flash_offset == REF_LINK_NODE) {
+			p = &ref->next_in_ino;
+			ref = *p;
+			continue;
+		}
+		i--;
+		ref++;
+	}
+	jeb->allocated_refs = nr;
+
+	dbg_memalloc("Reserved %d refs for block @0x%08x, last_node is %p (%08x,%p)\n",
+		  nr, jeb->offset, jeb->last_node, jeb->last_node->flash_offset,
+		  jeb->last_node->next_in_ino);
+
+	return 0;
+}
+
+void jffs2_free_refblock(struct jffs2_raw_node_ref *x)
+{
+	dbg_memalloc("%p\n", x);
+	kmem_cache_free(raw_node_ref_slab, x);
+}
+
+struct jffs2_node_frag *jffs2_alloc_node_frag(void)
+{
+	struct jffs2_node_frag *ret;
+	ret = kmem_cache_alloc(node_frag_slab, GFP_KERNEL);
+	dbg_memalloc("%p\n", ret);
+	return ret;
+}
+
+void jffs2_free_node_frag(struct jffs2_node_frag *x)
+{
+	dbg_memalloc("%p\n", x);
+	kmem_cache_free(node_frag_slab, x);
+}
+
+struct jffs2_inode_cache *jffs2_alloc_inode_cache(void)
+{
+	struct jffs2_inode_cache *ret;
+	ret = kmem_cache_alloc(inode_cache_slab, GFP_KERNEL);
+	dbg_memalloc("%p\n", ret);
+	return ret;
+}
+
+void jffs2_free_inode_cache(struct jffs2_inode_cache *x)
+{
+	dbg_memalloc("%p\n", x);
+	kmem_cache_free(inode_cache_slab, x);
+}
+
+#ifdef CONFIG_JFFS2_FS_XATTR
+struct jffs2_xattr_datum *jffs2_alloc_xattr_datum(void)
+{
+	struct jffs2_xattr_datum *xd;
+	xd = kmem_cache_zalloc(xattr_datum_cache, GFP_KERNEL);
+	dbg_memalloc("%p\n", xd);
+	if (!xd)
+		return NULL;
+
+	xd->class = RAWNODE_CLASS_XATTR_DATUM;
+	xd->node = (void *)xd;
+	INIT_LIST_HEAD(&xd->xindex);
+	return xd;
+}
+
+void jffs2_free_xattr_datum(struct jffs2_xattr_datum *xd)
+{
+	dbg_memalloc("%p\n", xd);
+	kmem_cache_free(xattr_datum_cache, xd);
+}
+
+struct jffs2_xattr_ref *jffs2_alloc_xattr_ref(void)
+{
+	struct jffs2_xattr_ref *ref;
+	ref = kmem_cache_zalloc(xattr_ref_cache, GFP_KERNEL);
+	dbg_memalloc("%p\n", ref);
+	if (!ref)
+		return NULL;
+
+	ref->class = RAWNODE_CLASS_XATTR_REF;
+	ref->node = (void *)ref;
+	return ref;
+}
+
+void jffs2_free_xattr_ref(struct jffs2_xattr_ref *ref)
+{
+	dbg_memalloc("%p\n", ref);
+	kmem_cache_free(xattr_ref_cache, ref);
+}
+#endif