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, 239 insertions, 0 deletions

diff --git a/include/trace/events/spi.h b/include/trace/events/spi.h
new file mode 100644
index 000000000..e63d4a24d
--- /dev/null
+++ b/include/trace/events/spi.h
@@ -0,0 +1,239 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM spi
+
+#if !defined(_TRACE_SPI_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_SPI_H
+
+#include <linux/ktime.h>
+#include <linux/tracepoint.h>
+
+DECLARE_EVENT_CLASS(spi_controller,
+
+	TP_PROTO(struct spi_controller *controller),
+
+	TP_ARGS(controller),
+
+	TP_STRUCT__entry(
+		__field(        int,           bus_num             )
+	),
+
+	TP_fast_assign(
+		__entry->bus_num = controller->bus_num;
+	),
+
+	TP_printk("spi%d", (int)__entry->bus_num)
+
+);
+
+DEFINE_EVENT(spi_controller, spi_controller_idle,
+
+	TP_PROTO(struct spi_controller *controller),
+
+	TP_ARGS(controller)
+
+);
+
+DEFINE_EVENT(spi_controller, spi_controller_busy,
+
+	TP_PROTO(struct spi_controller *controller),
+
+	TP_ARGS(controller)
+
+);
+
+TRACE_EVENT(spi_setup,
+	TP_PROTO(struct spi_device *spi, int status),
+	TP_ARGS(spi, status),
+
+	TP_STRUCT__entry(
+		__field(int, bus_num)
+		__field(int, chip_select)
+		__field(unsigned long, mode)
+		__field(unsigned int, bits_per_word)
+		__field(unsigned int, max_speed_hz)
+		__field(int, status)
+	),
+
+	TP_fast_assign(
+		__entry->bus_num = spi->controller->bus_num;
+		__entry->chip_select =  spi_get_chipselect(spi, 0);
+		__entry->mode = spi->mode;
+		__entry->bits_per_word = spi->bits_per_word;
+		__entry->max_speed_hz = spi->max_speed_hz;
+		__entry->status = status;
+	),
+
+	TP_printk("spi%d.%d setup mode %lu, %s%s%s%s%u bits/w, %u Hz max --> %d",
+		  __entry->bus_num, __entry->chip_select,
+		  (__entry->mode & SPI_MODE_X_MASK),
+		  (__entry->mode & SPI_CS_HIGH) ? "cs_high, " : "",
+		  (__entry->mode & SPI_LSB_FIRST) ? "lsb, " : "",
+		  (__entry->mode & SPI_3WIRE) ? "3wire, " : "",
+		  (__entry->mode & SPI_LOOP) ? "loopback, " : "",
+		  __entry->bits_per_word, __entry->max_speed_hz,
+		  __entry->status)
+);
+
+TRACE_EVENT(spi_set_cs,
+	TP_PROTO(struct spi_device *spi, bool enable),
+	TP_ARGS(spi, enable),
+
+	TP_STRUCT__entry(
+		__field(int, bus_num)
+		__field(int, chip_select)
+		__field(unsigned long, mode)
+		__field(bool, enable)
+	),
+
+	TP_fast_assign(
+		__entry->bus_num = spi->controller->bus_num;
+		__entry->chip_select = spi_get_chipselect(spi, 0);
+		__entry->mode = spi->mode;
+		__entry->enable = enable;
+	),
+
+	TP_printk("spi%d.%d %s%s",
+		  __entry->bus_num, __entry->chip_select,
+		  __entry->enable ? "activate" : "deactivate",
+		  (__entry->mode & SPI_CS_HIGH) ? ", cs_high" : "")
+);
+
+DECLARE_EVENT_CLASS(spi_message,
+
+	TP_PROTO(struct spi_message *msg),
+
+	TP_ARGS(msg),
+
+	TP_STRUCT__entry(
+		__field(        int,            bus_num         )
+		__field(        int,            chip_select     )
+		__field(        struct spi_message *,   msg     )
+	),
+
+	TP_fast_assign(
+		__entry->bus_num = msg->spi->controller->bus_num;
+		__entry->chip_select = spi_get_chipselect(msg->spi, 0);
+		__entry->msg = msg;
+	),
+
+        TP_printk("spi%d.%d %p", (int)__entry->bus_num,
+		  (int)__entry->chip_select,
+		  (struct spi_message *)__entry->msg)
+);
+
+DEFINE_EVENT(spi_message, spi_message_submit,
+
+	TP_PROTO(struct spi_message *msg),
+
+	TP_ARGS(msg)
+
+);
+
+DEFINE_EVENT(spi_message, spi_message_start,
+
+	TP_PROTO(struct spi_message *msg),
+
+	TP_ARGS(msg)
+
+);
+
+TRACE_EVENT(spi_message_done,
+
+	TP_PROTO(struct spi_message *msg),
+
+	TP_ARGS(msg),
+
+	TP_STRUCT__entry(
+		__field(        int,            bus_num         )
+		__field(        int,            chip_select     )
+		__field(        struct spi_message *,   msg     )
+		__field(        unsigned,       frame           )
+		__field(        unsigned,       actual          )
+	),
+
+	TP_fast_assign(
+		__entry->bus_num = msg->spi->controller->bus_num;
+		__entry->chip_select = spi_get_chipselect(msg->spi, 0);
+		__entry->msg = msg;
+		__entry->frame = msg->frame_length;
+		__entry->actual = msg->actual_length;
+	),
+
+        TP_printk("spi%d.%d %p len=%u/%u", (int)__entry->bus_num,
+		  (int)__entry->chip_select,
+		  (struct spi_message *)__entry->msg,
+                  (unsigned)__entry->actual, (unsigned)__entry->frame)
+);
+
+/*
+ * Consider a buffer valid if non-NULL and if it doesn't match the dummy buffer
+ * that only exist to work with controllers that have SPI_CONTROLLER_MUST_TX or
+ * SPI_CONTROLLER_MUST_RX.
+ */
+#define spi_valid_txbuf(msg, xfer) \
+	(xfer->tx_buf && xfer->tx_buf != msg->spi->controller->dummy_tx)
+#define spi_valid_rxbuf(msg, xfer) \
+	(xfer->rx_buf && xfer->rx_buf != msg->spi->controller->dummy_rx)
+
+DECLARE_EVENT_CLASS(spi_transfer,
+
+	TP_PROTO(struct spi_message *msg, struct spi_transfer *xfer),
+
+	TP_ARGS(msg, xfer),
+
+	TP_STRUCT__entry(
+		__field(        int,            bus_num         )
+		__field(        int,            chip_select     )
+		__field(        struct spi_transfer *,   xfer   )
+		__field(        int,            len             )
+		__dynamic_array(u8, rx_buf,
+				spi_valid_rxbuf(msg, xfer) ?
+					(xfer->len < 64 ? xfer->len : 64) : 0)
+		__dynamic_array(u8, tx_buf,
+				spi_valid_txbuf(msg, xfer) ?
+					(xfer->len < 64 ? xfer->len : 64) : 0)
+	),
+
+	TP_fast_assign(
+		__entry->bus_num = msg->spi->controller->bus_num;
+		__entry->chip_select = spi_get_chipselect(msg->spi, 0);
+		__entry->xfer = xfer;
+		__entry->len = xfer->len;
+
+		if (spi_valid_txbuf(msg, xfer))
+			memcpy(__get_dynamic_array(tx_buf),
+			       xfer->tx_buf, __get_dynamic_array_len(tx_buf));
+
+		if (spi_valid_rxbuf(msg, xfer))
+			memcpy(__get_dynamic_array(rx_buf),
+			       xfer->rx_buf, __get_dynamic_array_len(rx_buf));
+	),
+
+	TP_printk("spi%d.%d %p len=%d tx=[%*phD] rx=[%*phD]",
+		  __entry->bus_num, __entry->chip_select,
+		  __entry->xfer, __entry->len,
+		  __get_dynamic_array_len(tx_buf), __get_dynamic_array(tx_buf),
+		  __get_dynamic_array_len(rx_buf), __get_dynamic_array(rx_buf))
+);
+
+DEFINE_EVENT(spi_transfer, spi_transfer_start,
+
+	TP_PROTO(struct spi_message *msg, struct spi_transfer *xfer),
+
+	TP_ARGS(msg, xfer)
+
+);
+
+DEFINE_EVENT(spi_transfer, spi_transfer_stop,
+
+	TP_PROTO(struct spi_message *msg, struct spi_transfer *xfer),
+
+	TP_ARGS(msg, xfer)
+
+);
+
+#endif /* _TRACE_POWER_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>