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, 119 insertions, 0 deletions

diff --git a/fs/jffs2/compr.h b/fs/jffs2/compr.h
new file mode 100644
index 000000000..3716b6b79
--- /dev/null
+++ b/fs/jffs2/compr.h
@@ -0,0 +1,119 @@
+/*
+ * JFFS2 -- Journalling Flash File System, Version 2.
+ *
+ * Copyright © 2004   Ferenc Havasi <havasi@inf.u-szeged.hu>,
+ *		      University of Szeged, Hungary
+ * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org>
+ *
+ * For licensing information, see the file 'LICENCE' in this directory.
+ *
+ */
+
+#ifndef __JFFS2_COMPR_H__
+#define __JFFS2_COMPR_H__
+
+#include <linux/kernel.h>
+#include <linux/vmalloc.h>
+#include <linux/list.h>
+#include <linux/types.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/errno.h>
+#include <linux/fs.h>
+#include <linux/jffs2.h>
+#include "jffs2_fs_i.h"
+#include "jffs2_fs_sb.h"
+#include "nodelist.h"
+
+#define JFFS2_RUBINMIPS_PRIORITY 10
+#define JFFS2_DYNRUBIN_PRIORITY  20
+#define JFFS2_LZARI_PRIORITY     30
+#define JFFS2_RTIME_PRIORITY     50
+#define JFFS2_ZLIB_PRIORITY      60
+#define JFFS2_LZO_PRIORITY       80
+
+
+#define JFFS2_RUBINMIPS_DISABLED /* RUBINs will be used only */
+#define JFFS2_DYNRUBIN_DISABLED  /*	   for decompression */
+
+#define JFFS2_COMPR_MODE_NONE       0
+#define JFFS2_COMPR_MODE_PRIORITY   1
+#define JFFS2_COMPR_MODE_SIZE       2
+#define JFFS2_COMPR_MODE_FAVOURLZO  3
+#define JFFS2_COMPR_MODE_FORCELZO   4
+#define JFFS2_COMPR_MODE_FORCEZLIB  5
+
+#define FAVOUR_LZO_PERCENT 80
+
+struct jffs2_compressor {
+	struct list_head list;
+	int priority;			/* used by prirority comr. mode */
+	char *name;
+	char compr;			/* JFFS2_COMPR_XXX */
+	int (*compress)(unsigned char *data_in, unsigned char *cpage_out,
+			uint32_t *srclen, uint32_t *destlen);
+	int (*decompress)(unsigned char *cdata_in, unsigned char *data_out,
+			  uint32_t cdatalen, uint32_t datalen);
+	int usecount;
+	int disabled;		/* if set the compressor won't compress */
+	unsigned char *compr_buf;	/* used by size compr. mode */
+	uint32_t compr_buf_size;	/* used by size compr. mode */
+	uint32_t stat_compr_orig_size;
+	uint32_t stat_compr_new_size;
+	uint32_t stat_compr_blocks;
+	uint32_t stat_decompr_blocks;
+};
+
+int jffs2_register_compressor(struct jffs2_compressor *comp);
+int jffs2_unregister_compressor(struct jffs2_compressor *comp);
+
+int jffs2_compressors_init(void);
+int jffs2_compressors_exit(void);
+
+uint16_t jffs2_compress(struct jffs2_sb_info *c, struct jffs2_inode_info *f,
+			unsigned char *data_in, unsigned char **cpage_out,
+			uint32_t *datalen, uint32_t *cdatalen);
+
+int jffs2_decompress(struct jffs2_sb_info *c, struct jffs2_inode_info *f,
+		     uint16_t comprtype, unsigned char *cdata_in,
+		     unsigned char *data_out, uint32_t cdatalen, uint32_t datalen);
+
+void jffs2_free_comprbuf(unsigned char *comprbuf, unsigned char *orig);
+
+/* Compressor modules */
+/* These functions will be called by jffs2_compressors_init/exit */
+
+#ifdef CONFIG_JFFS2_RUBIN
+int jffs2_rubinmips_init(void);
+void jffs2_rubinmips_exit(void);
+int jffs2_dynrubin_init(void);
+void jffs2_dynrubin_exit(void);
+#else
+static inline int jffs2_rubinmips_init(void) { return 0; }
+static inline void jffs2_rubinmips_exit(void) {}
+static inline int jffs2_dynrubin_init(void) { return 0; }
+static inline void jffs2_dynrubin_exit(void) {}
+#endif
+#ifdef CONFIG_JFFS2_RTIME
+extern int jffs2_rtime_init(void);
+extern void jffs2_rtime_exit(void);
+#else
+static inline int jffs2_rtime_init(void) { return 0; }
+static inline void jffs2_rtime_exit(void) {}
+#endif
+#ifdef CONFIG_JFFS2_ZLIB
+extern int jffs2_zlib_init(void);
+extern void jffs2_zlib_exit(void);
+#else
+static inline int jffs2_zlib_init(void) { return 0; }
+static inline void jffs2_zlib_exit(void) {}
+#endif
+#ifdef CONFIG_JFFS2_LZO
+extern int jffs2_lzo_init(void);
+extern void jffs2_lzo_exit(void);
+#else
+static inline int jffs2_lzo_init(void) { return 0; }
+static inline void jffs2_lzo_exit(void) {}
+#endif
+
+#endif /* __JFFS2_COMPR_H__ */