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, 245 insertions, 0 deletions

diff --git a/include/trace/events/smbus.h b/include/trace/events/smbus.h
new file mode 100644
index 000000000..71a87edfc
--- /dev/null
+++ b/include/trace/events/smbus.h
@@ -0,0 +1,245 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* SMBUS message transfer tracepoints
+ *
+ * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM smbus
+
+#if !defined(_TRACE_SMBUS_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_SMBUS_H
+
+#include <linux/i2c.h>
+#include <linux/tracepoint.h>
+
+/*
+ * drivers/i2c/i2c-core-smbus.c
+ */
+
+/*
+ * i2c_smbus_xfer() write data or procedure call request
+ */
+TRACE_EVENT_CONDITION(smbus_write,
+	TP_PROTO(const struct i2c_adapter *adap,
+		 u16 addr, unsigned short flags,
+		 char read_write, u8 command, int protocol,
+		 const union i2c_smbus_data *data),
+	TP_ARGS(adap, addr, flags, read_write, command, protocol, data),
+	TP_CONDITION(read_write == I2C_SMBUS_WRITE ||
+		     protocol == I2C_SMBUS_PROC_CALL ||
+		     protocol == I2C_SMBUS_BLOCK_PROC_CALL),
+	TP_STRUCT__entry(
+		__field(int,	adapter_nr		)
+		__field(__u16,	addr			)
+		__field(__u16,	flags			)
+		__field(__u8,	command			)
+		__field(__u8,	len			)
+		__field(__u32,	protocol		)
+		__array(__u8, buf, I2C_SMBUS_BLOCK_MAX + 2)	),
+	TP_fast_assign(
+		__entry->adapter_nr = adap->nr;
+		__entry->addr = addr;
+		__entry->flags = flags;
+		__entry->command = command;
+		__entry->protocol = protocol;
+
+		switch (protocol) {
+		case I2C_SMBUS_BYTE_DATA:
+			__entry->len = 1;
+			goto copy;
+		case I2C_SMBUS_WORD_DATA:
+		case I2C_SMBUS_PROC_CALL:
+			__entry->len = 2;
+			goto copy;
+		case I2C_SMBUS_BLOCK_DATA:
+		case I2C_SMBUS_BLOCK_PROC_CALL:
+		case I2C_SMBUS_I2C_BLOCK_DATA:
+			__entry->len = data->block[0] + 1;
+		copy:
+			memcpy(__entry->buf, data->block, __entry->len);
+			break;
+		case I2C_SMBUS_QUICK:
+		case I2C_SMBUS_BYTE:
+		case I2C_SMBUS_I2C_BLOCK_BROKEN:
+		default:
+			__entry->len = 0;
+		}
+		       ),
+	TP_printk("i2c-%d a=%03x f=%04x c=%x %s l=%u [%*phD]",
+		  __entry->adapter_nr,
+		  __entry->addr,
+		  __entry->flags,
+		  __entry->command,
+		  __print_symbolic(__entry->protocol,
+				   { I2C_SMBUS_QUICK,		"QUICK"	},
+				   { I2C_SMBUS_BYTE,		"BYTE"	},
+				   { I2C_SMBUS_BYTE_DATA,		"BYTE_DATA" },
+				   { I2C_SMBUS_WORD_DATA,		"WORD_DATA" },
+				   { I2C_SMBUS_PROC_CALL,		"PROC_CALL" },
+				   { I2C_SMBUS_BLOCK_DATA,		"BLOCK_DATA" },
+				   { I2C_SMBUS_I2C_BLOCK_BROKEN,	"I2C_BLOCK_BROKEN" },
+				   { I2C_SMBUS_BLOCK_PROC_CALL,	"BLOCK_PROC_CALL" },
+				   { I2C_SMBUS_I2C_BLOCK_DATA,	"I2C_BLOCK_DATA" }),
+		  __entry->len,
+		  __entry->len, __entry->buf
+		  ));
+
+/*
+ * i2c_smbus_xfer() read data request
+ */
+TRACE_EVENT_CONDITION(smbus_read,
+	TP_PROTO(const struct i2c_adapter *adap,
+		 u16 addr, unsigned short flags,
+		 char read_write, u8 command, int protocol),
+	TP_ARGS(adap, addr, flags, read_write, command, protocol),
+	TP_CONDITION(!(read_write == I2C_SMBUS_WRITE ||
+		       protocol == I2C_SMBUS_PROC_CALL ||
+		       protocol == I2C_SMBUS_BLOCK_PROC_CALL)),
+	TP_STRUCT__entry(
+		__field(int,	adapter_nr		)
+		__field(__u16,	flags			)
+		__field(__u16,	addr			)
+		__field(__u8,	command			)
+		__field(__u32,	protocol		)
+		__array(__u8, buf, I2C_SMBUS_BLOCK_MAX + 2)	),
+	TP_fast_assign(
+		__entry->adapter_nr = adap->nr;
+		__entry->addr = addr;
+		__entry->flags = flags;
+		__entry->command = command;
+		__entry->protocol = protocol;
+		       ),
+	TP_printk("i2c-%d a=%03x f=%04x c=%x %s",
+		  __entry->adapter_nr,
+		  __entry->addr,
+		  __entry->flags,
+		  __entry->command,
+		  __print_symbolic(__entry->protocol,
+				   { I2C_SMBUS_QUICK,		"QUICK"	},
+				   { I2C_SMBUS_BYTE,		"BYTE"	},
+				   { I2C_SMBUS_BYTE_DATA,		"BYTE_DATA" },
+				   { I2C_SMBUS_WORD_DATA,		"WORD_DATA" },
+				   { I2C_SMBUS_PROC_CALL,		"PROC_CALL" },
+				   { I2C_SMBUS_BLOCK_DATA,		"BLOCK_DATA" },
+				   { I2C_SMBUS_I2C_BLOCK_BROKEN,	"I2C_BLOCK_BROKEN" },
+				   { I2C_SMBUS_BLOCK_PROC_CALL,	"BLOCK_PROC_CALL" },
+				   { I2C_SMBUS_I2C_BLOCK_DATA,	"I2C_BLOCK_DATA" })
+		  ));
+
+/*
+ * i2c_smbus_xfer() read data or procedure call reply
+ */
+TRACE_EVENT_CONDITION(smbus_reply,
+	TP_PROTO(const struct i2c_adapter *adap,
+		 u16 addr, unsigned short flags,
+		 char read_write, u8 command, int protocol,
+		 const union i2c_smbus_data *data, int res),
+	TP_ARGS(adap, addr, flags, read_write, command, protocol, data, res),
+	TP_CONDITION(res >= 0 && read_write == I2C_SMBUS_READ),
+	TP_STRUCT__entry(
+		__field(int,	adapter_nr		)
+		__field(__u16,	addr			)
+		__field(__u16,	flags			)
+		__field(__u8,	command			)
+		__field(__u8,	len			)
+		__field(__u32,	protocol		)
+		__array(__u8, buf, I2C_SMBUS_BLOCK_MAX + 2)	),
+	TP_fast_assign(
+		__entry->adapter_nr = adap->nr;
+		__entry->addr = addr;
+		__entry->flags = flags;
+		__entry->command = command;
+		__entry->protocol = protocol;
+
+		switch (protocol) {
+		case I2C_SMBUS_BYTE:
+		case I2C_SMBUS_BYTE_DATA:
+			__entry->len = 1;
+			goto copy;
+		case I2C_SMBUS_WORD_DATA:
+		case I2C_SMBUS_PROC_CALL:
+			__entry->len = 2;
+			goto copy;
+		case I2C_SMBUS_BLOCK_DATA:
+		case I2C_SMBUS_BLOCK_PROC_CALL:
+		case I2C_SMBUS_I2C_BLOCK_DATA:
+			__entry->len = data->block[0] + 1;
+		copy:
+			memcpy(__entry->buf, data->block, __entry->len);
+			break;
+		case I2C_SMBUS_QUICK:
+		case I2C_SMBUS_I2C_BLOCK_BROKEN:
+		default:
+			__entry->len = 0;
+		}
+		       ),
+	TP_printk("i2c-%d a=%03x f=%04x c=%x %s l=%u [%*phD]",
+		  __entry->adapter_nr,
+		  __entry->addr,
+		  __entry->flags,
+		  __entry->command,
+		  __print_symbolic(__entry->protocol,
+				   { I2C_SMBUS_QUICK,		"QUICK"	},
+				   { I2C_SMBUS_BYTE,		"BYTE"	},
+				   { I2C_SMBUS_BYTE_DATA,		"BYTE_DATA" },
+				   { I2C_SMBUS_WORD_DATA,		"WORD_DATA" },
+				   { I2C_SMBUS_PROC_CALL,		"PROC_CALL" },
+				   { I2C_SMBUS_BLOCK_DATA,		"BLOCK_DATA" },
+				   { I2C_SMBUS_I2C_BLOCK_BROKEN,	"I2C_BLOCK_BROKEN" },
+				   { I2C_SMBUS_BLOCK_PROC_CALL,	"BLOCK_PROC_CALL" },
+				   { I2C_SMBUS_I2C_BLOCK_DATA,	"I2C_BLOCK_DATA" }),
+		  __entry->len,
+		  __entry->len, __entry->buf
+		  ));
+
+/*
+ * i2c_smbus_xfer() result
+ */
+TRACE_EVENT(smbus_result,
+	    TP_PROTO(const struct i2c_adapter *adap,
+		     u16 addr, unsigned short flags,
+		     char read_write, u8 command, int protocol,
+		     int res),
+	    TP_ARGS(adap, addr, flags, read_write, command, protocol, res),
+	    TP_STRUCT__entry(
+		    __field(int,	adapter_nr		)
+		    __field(__u16,	addr			)
+		    __field(__u16,	flags			)
+		    __field(__u8,	read_write		)
+		    __field(__u8,	command			)
+		    __field(__s16,	res			)
+		    __field(__u32,	protocol		)
+			     ),
+	    TP_fast_assign(
+		    __entry->adapter_nr = adap->nr;
+		    __entry->addr = addr;
+		    __entry->flags = flags;
+		    __entry->read_write = read_write;
+		    __entry->command = command;
+		    __entry->protocol = protocol;
+		    __entry->res = res;
+			   ),
+	    TP_printk("i2c-%d a=%03x f=%04x c=%x %s %s res=%d",
+		      __entry->adapter_nr,
+		      __entry->addr,
+		      __entry->flags,
+		      __entry->command,
+		      __print_symbolic(__entry->protocol,
+				       { I2C_SMBUS_QUICK,		"QUICK"	},
+				       { I2C_SMBUS_BYTE,		"BYTE"	},
+				       { I2C_SMBUS_BYTE_DATA,		"BYTE_DATA" },
+				       { I2C_SMBUS_WORD_DATA,		"WORD_DATA" },
+				       { I2C_SMBUS_PROC_CALL,		"PROC_CALL" },
+				       { I2C_SMBUS_BLOCK_DATA,		"BLOCK_DATA" },
+				       { I2C_SMBUS_I2C_BLOCK_BROKEN,	"I2C_BLOCK_BROKEN" },
+				       { I2C_SMBUS_BLOCK_PROC_CALL,	"BLOCK_PROC_CALL" },
+				       { I2C_SMBUS_I2C_BLOCK_DATA,	"I2C_BLOCK_DATA" }),
+		      __entry->read_write == I2C_SMBUS_WRITE ? "wr" : "rd",
+		      __entry->res
+		      ));
+
+#endif /* _TRACE_SMBUS_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>