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, 122 insertions, 0 deletions

diff --git a/include/scsi/libiscsi_tcp.h b/include/scsi/libiscsi_tcp.h
new file mode 100644
index 000000000..ef53d4bea
--- /dev/null
+++ b/include/scsi/libiscsi_tcp.h
@@ -0,0 +1,122 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * iSCSI over TCP/IP Data-Path lib
+ *
+ * Copyright (C) 2008 Mike Christie
+ * Copyright (C) 2008 Red Hat, Inc.  All rights reserved.
+ * maintained by open-iscsi@googlegroups.com
+ */
+
+#ifndef LIBISCSI_TCP_H
+#define LIBISCSI_TCP_H
+
+#include <scsi/libiscsi.h>
+
+struct iscsi_tcp_conn;
+struct iscsi_segment;
+struct sk_buff;
+
+typedef int iscsi_segment_done_fn_t(struct iscsi_tcp_conn *,
+				    struct iscsi_segment *);
+
+struct iscsi_segment {
+	unsigned char		*data;
+	unsigned int		size;
+	unsigned int		copied;
+	unsigned int		total_size;
+	unsigned int		total_copied;
+
+	u32			*crcp;
+	unsigned char		padbuf[ISCSI_PAD_LEN];
+	unsigned char		recv_digest[ISCSI_DIGEST_SIZE];
+	unsigned char		digest[ISCSI_DIGEST_SIZE];
+	unsigned int		digest_len;
+
+	struct scatterlist	*sg;
+	void			*sg_mapped;
+	unsigned int		sg_offset;
+	bool			atomic_mapped;
+
+	iscsi_segment_done_fn_t	*done;
+};
+
+/* Socket connection receive helper */
+struct iscsi_tcp_recv {
+	struct iscsi_hdr	*hdr;
+	struct iscsi_segment	segment;
+
+	/* Allocate buffer for BHS + AHS */
+	uint32_t		hdr_buf[64];
+
+	/* copied and flipped values */
+	int			datalen;
+};
+
+struct iscsi_tcp_conn {
+	struct iscsi_conn	*iscsi_conn;
+	void			*dd_data;
+	int			stop_stage;	/* conn_stop() flag: *
+						 * stop to recover,  *
+						 * stop to terminate */
+	/* control data */
+	struct iscsi_tcp_recv	in;		/* TCP receive context */
+	/* CRC32C (Rx) LLD should set this if they do not offload */
+	u32			*rx_crcp;
+};
+
+struct iscsi_tcp_task {
+	uint32_t		exp_datasn;	/* expected target's R2TSN/DataSN */
+	int			data_offset;
+	struct iscsi_r2t_info	*r2t;		/* in progress solict R2T */
+	struct iscsi_pool	r2tpool;
+	struct kfifo		r2tqueue;
+	void			*dd_data;
+	spinlock_t		pool2queue;
+	spinlock_t		queue2pool;
+};
+
+enum {
+	ISCSI_TCP_SEGMENT_DONE,		/* curr seg has been processed */
+	ISCSI_TCP_SKB_DONE,		/* skb is out of data */
+	ISCSI_TCP_CONN_ERR,		/* iscsi layer has fired a conn err */
+	ISCSI_TCP_SUSPENDED,		/* conn is suspended */
+};
+
+extern void iscsi_tcp_hdr_recv_prep(struct iscsi_tcp_conn *tcp_conn);
+extern int iscsi_tcp_recv_skb(struct iscsi_conn *conn, struct sk_buff *skb,
+			      unsigned int offset, bool offloaded, int *status);
+extern void iscsi_tcp_cleanup_task(struct iscsi_task *task);
+extern int iscsi_tcp_task_init(struct iscsi_task *task);
+extern int iscsi_tcp_task_xmit(struct iscsi_task *task);
+
+/* segment helpers */
+extern int iscsi_tcp_recv_segment_is_hdr(struct iscsi_tcp_conn *tcp_conn);
+extern int iscsi_tcp_segment_done(struct iscsi_tcp_conn *tcp_conn,
+				  struct iscsi_segment *segment, int recv,
+				  unsigned copied);
+extern void iscsi_tcp_segment_unmap(struct iscsi_segment *segment);
+
+extern void iscsi_segment_init_linear(struct iscsi_segment *segment,
+				      void *data, size_t size,
+				      iscsi_segment_done_fn_t *done, u32 *crcp);
+extern int
+iscsi_segment_seek_sg(struct iscsi_segment *segment,
+		      struct scatterlist *sg_list, unsigned int sg_count,
+		      unsigned int offset, size_t size,
+		      iscsi_segment_done_fn_t *done, u32 *crcp);
+
+/* digest helpers */
+extern void iscsi_tcp_dgst_header(const void *hdr, size_t hdrlen,
+				  unsigned char digest[ISCSI_DIGEST_SIZE]);
+extern struct iscsi_cls_conn *
+iscsi_tcp_conn_setup(struct iscsi_cls_session *cls_session, int dd_data_size,
+		     uint32_t conn_idx);
+extern void iscsi_tcp_conn_teardown(struct iscsi_cls_conn *cls_conn);
+
+/* misc helpers */
+extern int iscsi_tcp_r2tpool_alloc(struct iscsi_session *session);
+extern void iscsi_tcp_r2tpool_free(struct iscsi_session *session);
+extern int iscsi_tcp_set_max_r2t(struct iscsi_conn *conn, char *buf);
+extern void iscsi_tcp_conn_get_stats(struct iscsi_cls_conn *cls_conn,
+				     struct iscsi_stats *stats);
+#endif /* LIBISCSI_TCP_H */