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, 144 insertions, 0 deletions

diff --git a/drivers/thunderbolt/ctl.h b/drivers/thunderbolt/ctl.h
new file mode 100644
index 000000000..db1646eb4
--- /dev/null
+++ b/drivers/thunderbolt/ctl.h
@@ -0,0 +1,144 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Thunderbolt driver - control channel and configuration commands
+ *
+ * Copyright (c) 2014 Andreas Noever <andreas.noever@gmail.com>
+ * Copyright (C) 2018, Intel Corporation
+ */
+
+#ifndef _TB_CFG
+#define _TB_CFG
+
+#include <linux/kref.h>
+#include <linux/thunderbolt.h>
+
+#include "nhi.h"
+#include "tb_msgs.h"
+
+/* control channel */
+struct tb_ctl;
+
+typedef bool (*event_cb)(void *data, enum tb_cfg_pkg_type type,
+			 const void *buf, size_t size);
+
+struct tb_ctl *tb_ctl_alloc(struct tb_nhi *nhi, int index, int timeout_msec,
+			    event_cb cb, void *cb_data);
+void tb_ctl_start(struct tb_ctl *ctl);
+void tb_ctl_stop(struct tb_ctl *ctl);
+void tb_ctl_free(struct tb_ctl *ctl);
+
+/* configuration commands */
+
+struct tb_cfg_result {
+	u64 response_route;
+	u32 response_port; /*
+			    * If err = 1 then this is the port that send the
+			    * error.
+			    * If err = 0 and if this was a cfg_read/write then
+			    * this is the upstream port of the responding
+			    * switch.
+			    * Otherwise the field is set to zero.
+			    */
+	int err; /* negative errors, 0 for success, 1 for tb errors */
+	enum tb_cfg_error tb_error; /* valid if err == 1 */
+};
+
+struct ctl_pkg {
+	struct tb_ctl *ctl;
+	void *buffer;
+	struct ring_frame frame;
+};
+
+/**
+ * struct tb_cfg_request - Control channel request
+ * @kref: Reference count
+ * @ctl: Pointer to the control channel structure. Only set when the
+ *	 request is queued.
+ * @request: Request is stored here
+ * @request_size: Size of the request packet (in bytes)
+ * @request_type: Type of the request packet
+ * @response: Response is stored here
+ * @response_size: Maximum size of one response packet
+ * @response_type: Expected type of the response packet
+ * @npackets: Number of packets expected to be returned with this request
+ * @match: Function used to match the incoming packet
+ * @copy: Function used to copy the incoming packet to @response
+ * @callback: Callback called when the request is finished successfully
+ * @callback_data: Data to be passed to @callback
+ * @flags: Flags for the request
+ * @work: Work item used to complete the request
+ * @result: Result after the request has been completed
+ * @list: Requests are queued using this field
+ *
+ * An arbitrary request over Thunderbolt control channel. For standard
+ * control channel message, one should use tb_cfg_read/write() and
+ * friends if possible.
+ */
+struct tb_cfg_request {
+	struct kref kref;
+	struct tb_ctl *ctl;
+	const void *request;
+	size_t request_size;
+	enum tb_cfg_pkg_type request_type;
+	void *response;
+	size_t response_size;
+	enum tb_cfg_pkg_type response_type;
+	size_t npackets;
+	bool (*match)(const struct tb_cfg_request *req,
+		      const struct ctl_pkg *pkg);
+	bool (*copy)(struct tb_cfg_request *req, const struct ctl_pkg *pkg);
+	void (*callback)(void *callback_data);
+	void *callback_data;
+	unsigned long flags;
+	struct work_struct work;
+	struct tb_cfg_result result;
+	struct list_head list;
+};
+
+#define TB_CFG_REQUEST_ACTIVE		0
+#define TB_CFG_REQUEST_CANCELED		1
+
+struct tb_cfg_request *tb_cfg_request_alloc(void);
+void tb_cfg_request_get(struct tb_cfg_request *req);
+void tb_cfg_request_put(struct tb_cfg_request *req);
+int tb_cfg_request(struct tb_ctl *ctl, struct tb_cfg_request *req,
+		   void (*callback)(void *), void *callback_data);
+void tb_cfg_request_cancel(struct tb_cfg_request *req, int err);
+struct tb_cfg_result tb_cfg_request_sync(struct tb_ctl *ctl,
+			struct tb_cfg_request *req, int timeout_msec);
+
+static inline u64 tb_cfg_get_route(const struct tb_cfg_header *header)
+{
+	return (u64) header->route_hi << 32 | header->route_lo;
+}
+
+static inline struct tb_cfg_header tb_cfg_make_header(u64 route)
+{
+	struct tb_cfg_header header = {
+		.route_hi = route >> 32,
+		.route_lo = route,
+	};
+	/* check for overflow, route_hi is not 32 bits! */
+	WARN_ON(tb_cfg_get_route(&header) != route);
+	return header;
+}
+
+int tb_cfg_ack_notification(struct tb_ctl *ctl, u64 route,
+			    const struct cfg_error_pkg *error);
+int tb_cfg_ack_plug(struct tb_ctl *ctl, u64 route, u32 port, bool unplug);
+struct tb_cfg_result tb_cfg_reset(struct tb_ctl *ctl, u64 route);
+struct tb_cfg_result tb_cfg_read_raw(struct tb_ctl *ctl, void *buffer,
+				     u64 route, u32 port,
+				     enum tb_cfg_space space, u32 offset,
+				     u32 length, int timeout_msec);
+struct tb_cfg_result tb_cfg_write_raw(struct tb_ctl *ctl, const void *buffer,
+				      u64 route, u32 port,
+				      enum tb_cfg_space space, u32 offset,
+				      u32 length, int timeout_msec);
+int tb_cfg_read(struct tb_ctl *ctl, void *buffer, u64 route, u32 port,
+		enum tb_cfg_space space, u32 offset, u32 length);
+int tb_cfg_write(struct tb_ctl *ctl, const void *buffer, u64 route, u32 port,
+		 enum tb_cfg_space space, u32 offset, u32 length);
+int tb_cfg_get_upstream_port(struct tb_ctl *ctl, u64 route);
+
+#endif