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, 197 insertions, 0 deletions

diff --git a/drivers/thunderbolt/trace.h b/drivers/thunderbolt/trace.h
new file mode 100644
index 000000000..6d0776514
--- /dev/null
+++ b/drivers/thunderbolt/trace.h
@@ -0,0 +1,197 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Thunderbolt tracing support
+ *
+ * Copyright (C) 2024, Intel Corporation
+ * Author: Mika Westerberg <mika.westerberg@linux.intel.com>
+ *	   Gil Fine <gil.fine@intel.com>
+ */
+
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM thunderbolt
+
+#if !defined(TB_TRACE_H_) || defined(TRACE_HEADER_MULTI_READ)
+#define TB_TRACE_H_
+
+#include <linux/trace_seq.h>
+#include <linux/tracepoint.h>
+
+#include "tb_msgs.h"
+
+#define tb_cfg_type_name(type)		{ type, #type }
+#define show_type_name(val)					\
+	__print_symbolic(val,					\
+		tb_cfg_type_name(TB_CFG_PKG_READ),		\
+		tb_cfg_type_name(TB_CFG_PKG_WRITE),		\
+		tb_cfg_type_name(TB_CFG_PKG_ERROR),		\
+		tb_cfg_type_name(TB_CFG_PKG_NOTIFY_ACK),	\
+		tb_cfg_type_name(TB_CFG_PKG_EVENT),		\
+		tb_cfg_type_name(TB_CFG_PKG_XDOMAIN_REQ),	\
+		tb_cfg_type_name(TB_CFG_PKG_XDOMAIN_RESP),	\
+		tb_cfg_type_name(TB_CFG_PKG_OVERRIDE),		\
+		tb_cfg_type_name(TB_CFG_PKG_RESET),		\
+		tb_cfg_type_name(TB_CFG_PKG_ICM_EVENT),		\
+		tb_cfg_type_name(TB_CFG_PKG_ICM_CMD),		\
+		tb_cfg_type_name(TB_CFG_PKG_ICM_RESP))
+
+#ifndef TB_TRACE_HELPERS
+#define TB_TRACE_HELPERS
+static inline const char *show_data_read_write(struct trace_seq *p,
+					       const u32 *data)
+{
+	const struct cfg_read_pkg *msg = (const struct cfg_read_pkg *)data;
+	const char *ret = trace_seq_buffer_ptr(p);
+
+	trace_seq_printf(p, "offset=%#x, len=%u, port=%d, config=%#x, seq=%d, ",
+			 msg->addr.offset, msg->addr.length, msg->addr.port,
+			 msg->addr.space, msg->addr.seq);
+
+	return ret;
+}
+
+static inline const char *show_data_error(struct trace_seq *p, const u32 *data)
+{
+	const struct cfg_error_pkg *msg = (const struct cfg_error_pkg *)data;
+	const char *ret = trace_seq_buffer_ptr(p);
+
+	trace_seq_printf(p, "error=%#x, port=%d, plug=%#x, ", msg->error,
+			 msg->port, msg->pg);
+
+	return ret;
+}
+
+static inline const char *show_data_event(struct trace_seq *p, const u32 *data)
+{
+	const struct cfg_event_pkg *msg = (const struct cfg_event_pkg *)data;
+	const char *ret = trace_seq_buffer_ptr(p);
+
+	trace_seq_printf(p, "port=%d, unplug=%#x, ", msg->port, msg->unplug);
+
+	return ret;
+}
+
+static inline const char *show_route(struct trace_seq *p, const u32 *data)
+{
+	const struct tb_cfg_header *header = (const struct tb_cfg_header *)data;
+	const char *ret = trace_seq_buffer_ptr(p);
+
+	trace_seq_printf(p, "route=%llx, ", tb_cfg_get_route(header));
+
+	return ret;
+}
+
+static inline const char *show_data(struct trace_seq *p, u8 type,
+				    const u32 *data, u32 length)
+{
+	const char *ret = trace_seq_buffer_ptr(p);
+	const char *prefix = "";
+	int i;
+
+	switch (type) {
+	case TB_CFG_PKG_READ:
+	case TB_CFG_PKG_WRITE:
+		show_route(p, data);
+		show_data_read_write(p, data);
+		break;
+
+	case TB_CFG_PKG_ERROR:
+		show_route(p, data);
+		show_data_error(p, data);
+		break;
+
+	case TB_CFG_PKG_EVENT:
+		show_route(p, data);
+		show_data_event(p, data);
+		break;
+
+	case TB_CFG_PKG_ICM_EVENT:
+	case TB_CFG_PKG_ICM_CMD:
+	case TB_CFG_PKG_ICM_RESP:
+		/* ICM messages always target the host router */
+		trace_seq_puts(p, "route=0, ");
+		break;
+
+	default:
+		show_route(p, data);
+		break;
+	}
+
+	trace_seq_printf(p, "data=[");
+	for (i = 0; i < length; i++) {
+		trace_seq_printf(p, "%s0x%08x", prefix, data[i]);
+		prefix = ", ";
+	}
+	trace_seq_printf(p, "]");
+	trace_seq_putc(p, 0);
+
+	return ret;
+}
+#endif
+
+DECLARE_EVENT_CLASS(tb_raw,
+	TP_PROTO(int index, u8 type, const void *data, size_t size),
+	TP_ARGS(index, type, data, size),
+	TP_STRUCT__entry(
+		__field(int, index)
+		__field(u8, type)
+		__field(size_t, size)
+		__dynamic_array(u32, data, size / 4)
+	),
+	TP_fast_assign(
+		__entry->index = index;
+		__entry->type = type;
+		__entry->size = size / 4;
+		memcpy(__get_dynamic_array(data), data, size);
+	),
+	TP_printk("type=%s, size=%zd, domain=%d, %s",
+		  show_type_name(__entry->type), __entry->size, __entry->index,
+		  show_data(p, __entry->type, __get_dynamic_array(data),
+			    __entry->size)
+	)
+);
+
+DEFINE_EVENT(tb_raw, tb_tx,
+	TP_PROTO(int index, u8 type, const void *data, size_t size),
+	TP_ARGS(index, type, data, size)
+);
+
+DEFINE_EVENT(tb_raw, tb_event,
+	TP_PROTO(int index, u8 type, const void *data, size_t size),
+	TP_ARGS(index, type, data, size)
+);
+
+TRACE_EVENT(tb_rx,
+	TP_PROTO(int index, u8 type, const void *data, size_t size, bool dropped),
+	TP_ARGS(index, type, data, size, dropped),
+	TP_STRUCT__entry(
+		__field(int, index)
+		__field(u8, type)
+		__field(size_t, size)
+		__dynamic_array(u32, data, size / 4)
+		__field(bool, dropped)
+	),
+	TP_fast_assign(
+		__entry->index = index;
+		__entry->type = type;
+		__entry->size = size / 4;
+		memcpy(__get_dynamic_array(data), data, size);
+		__entry->dropped = dropped;
+	),
+	TP_printk("type=%s, dropped=%u, size=%zd, domain=%d, %s",
+		  show_type_name(__entry->type), __entry->dropped,
+		  __entry->size, __entry->index,
+		  show_data(p, __entry->type, __get_dynamic_array(data),
+			    __entry->size)
+	)
+);
+
+#endif /* TB_TRACE_H_ */
+
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH .
+
+#undef TRACE_INCLUDE_FILE
+#define TRACE_INCLUDE_FILE trace
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>