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, 284 insertions, 0 deletions

diff --git a/drivers/base/regmap/trace.h b/drivers/base/regmap/trace.h
new file mode 100644
index 000000000..bcc5a8b22
--- /dev/null
+++ b/drivers/base/regmap/trace.h
@@ -0,0 +1,284 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM regmap
+
+#if !defined(_TRACE_REGMAP_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_REGMAP_H
+
+#include <linux/ktime.h>
+#include <linux/tracepoint.h>
+
+#include "internal.h"
+
+/*
+ * Log register events
+ */
+DECLARE_EVENT_CLASS(regmap_reg,
+
+	TP_PROTO(struct regmap *map, unsigned int reg,
+		 unsigned int val),
+
+	TP_ARGS(map, reg, val),
+
+	TP_STRUCT__entry(
+		__string(	name,		regmap_name(map)	)
+		__field(	unsigned int,	reg			)
+		__field(	unsigned int,	val			)
+	),
+
+	TP_fast_assign(
+		__assign_str(name);
+		__entry->reg = reg;
+		__entry->val = val;
+	),
+
+	TP_printk("%s reg=%x val=%x", __get_str(name), __entry->reg, __entry->val)
+);
+
+DEFINE_EVENT(regmap_reg, regmap_reg_write,
+
+	TP_PROTO(struct regmap *map, unsigned int reg,
+		 unsigned int val),
+
+	TP_ARGS(map, reg, val)
+);
+
+DEFINE_EVENT(regmap_reg, regmap_reg_read,
+
+	TP_PROTO(struct regmap *map, unsigned int reg,
+		 unsigned int val),
+
+	TP_ARGS(map, reg, val)
+);
+
+DEFINE_EVENT(regmap_reg, regmap_reg_read_cache,
+
+	TP_PROTO(struct regmap *map, unsigned int reg,
+		 unsigned int val),
+
+	TP_ARGS(map, reg, val)
+);
+
+DECLARE_EVENT_CLASS(regmap_bulk,
+
+	TP_PROTO(struct regmap *map, unsigned int reg,
+		 const void *val, int val_len),
+
+	TP_ARGS(map, reg, val, val_len),
+
+	TP_STRUCT__entry(
+		__string(name, regmap_name(map))
+		__field(unsigned int, reg)
+		__dynamic_array(char, buf, val_len)
+		__field(int, val_len)
+	),
+
+	TP_fast_assign(
+		__assign_str(name);
+		__entry->reg = reg;
+		__entry->val_len = val_len;
+		memcpy(__get_dynamic_array(buf), val, val_len);
+	),
+
+	TP_printk("%s reg=%x val=%s", __get_str(name), __entry->reg,
+		  __print_hex(__get_dynamic_array(buf), __entry->val_len))
+);
+
+DEFINE_EVENT(regmap_bulk, regmap_bulk_write,
+
+	TP_PROTO(struct regmap *map, unsigned int reg,
+		 const void *val, int val_len),
+
+	TP_ARGS(map, reg, val, val_len)
+);
+
+DEFINE_EVENT(regmap_bulk, regmap_bulk_read,
+
+	TP_PROTO(struct regmap *map, unsigned int reg,
+		 const void *val, int val_len),
+
+	TP_ARGS(map, reg, val, val_len)
+);
+
+DECLARE_EVENT_CLASS(regmap_block,
+
+	TP_PROTO(struct regmap *map, unsigned int reg, int count),
+
+	TP_ARGS(map, reg, count),
+
+	TP_STRUCT__entry(
+		__string(	name,		regmap_name(map)	)
+		__field(	unsigned int,	reg			)
+		__field(	int,		count			)
+	),
+
+	TP_fast_assign(
+		__assign_str(name);
+		__entry->reg = reg;
+		__entry->count = count;
+	),
+
+	TP_printk("%s reg=%x count=%d", __get_str(name), __entry->reg, __entry->count)
+);
+
+DEFINE_EVENT(regmap_block, regmap_hw_read_start,
+
+	TP_PROTO(struct regmap *map, unsigned int reg, int count),
+
+	TP_ARGS(map, reg, count)
+);
+
+DEFINE_EVENT(regmap_block, regmap_hw_read_done,
+
+	TP_PROTO(struct regmap *map, unsigned int reg, int count),
+
+	TP_ARGS(map, reg, count)
+);
+
+DEFINE_EVENT(regmap_block, regmap_hw_write_start,
+
+	TP_PROTO(struct regmap *map, unsigned int reg, int count),
+
+	TP_ARGS(map, reg, count)
+);
+
+DEFINE_EVENT(regmap_block, regmap_hw_write_done,
+
+	TP_PROTO(struct regmap *map, unsigned int reg, int count),
+
+	TP_ARGS(map, reg, count)
+);
+
+TRACE_EVENT(regcache_sync,
+
+	TP_PROTO(struct regmap *map, const char *type,
+		 const char *status),
+
+	TP_ARGS(map, type, status),
+
+	TP_STRUCT__entry(
+		__string(       name,           regmap_name(map)	)
+		__string(	status,		status			)
+		__string(	type,		type			)
+	),
+
+	TP_fast_assign(
+		__assign_str(name);
+		__assign_str(status);
+		__assign_str(type);
+	),
+
+	TP_printk("%s type=%s status=%s", __get_str(name),
+		  __get_str(type), __get_str(status))
+);
+
+DECLARE_EVENT_CLASS(regmap_bool,
+
+	TP_PROTO(struct regmap *map, bool flag),
+
+	TP_ARGS(map, flag),
+
+	TP_STRUCT__entry(
+		__string(	name,		regmap_name(map)	)
+		__field(	int,		flag			)
+	),
+
+	TP_fast_assign(
+		__assign_str(name);
+		__entry->flag = flag;
+	),
+
+	TP_printk("%s flag=%d", __get_str(name), __entry->flag)
+);
+
+DEFINE_EVENT(regmap_bool, regmap_cache_only,
+
+	TP_PROTO(struct regmap *map, bool flag),
+
+	TP_ARGS(map, flag)
+);
+
+DEFINE_EVENT(regmap_bool, regmap_cache_bypass,
+
+	TP_PROTO(struct regmap *map, bool flag),
+
+	TP_ARGS(map, flag)
+);
+
+DECLARE_EVENT_CLASS(regmap_async,
+
+	TP_PROTO(struct regmap *map),
+
+	TP_ARGS(map),
+
+	TP_STRUCT__entry(
+		__string(	name,		regmap_name(map)	)
+	),
+
+	TP_fast_assign(
+		__assign_str(name);
+	),
+
+	TP_printk("%s", __get_str(name))
+);
+
+DEFINE_EVENT(regmap_block, regmap_async_write_start,
+
+	TP_PROTO(struct regmap *map, unsigned int reg, int count),
+
+	TP_ARGS(map, reg, count)
+);
+
+DEFINE_EVENT(regmap_async, regmap_async_io_complete,
+
+	TP_PROTO(struct regmap *map),
+
+	TP_ARGS(map)
+);
+
+DEFINE_EVENT(regmap_async, regmap_async_complete_start,
+
+	TP_PROTO(struct regmap *map),
+
+	TP_ARGS(map)
+);
+
+DEFINE_EVENT(regmap_async, regmap_async_complete_done,
+
+	TP_PROTO(struct regmap *map),
+
+	TP_ARGS(map)
+);
+
+TRACE_EVENT(regcache_drop_region,
+
+	TP_PROTO(struct regmap *map, unsigned int from,
+		 unsigned int to),
+
+	TP_ARGS(map, from, to),
+
+	TP_STRUCT__entry(
+		__string(       name,           regmap_name(map)	)
+		__field(	unsigned int,	from			)
+		__field(	unsigned int,	to			)
+	),
+
+	TP_fast_assign(
+		__assign_str(name);
+		__entry->from = from;
+		__entry->to = to;
+	),
+
+	TP_printk("%s %u-%u", __get_str(name), __entry->from, __entry->to)
+);
+
+#endif /* _TRACE_REGMAP_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>