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, 141 insertions, 0 deletions

diff --git a/drivers/gpib/include/nec7210.h b/drivers/gpib/include/nec7210.h
new file mode 100644
index 000000000..9835aa5ef
--- /dev/null
+++ b/drivers/gpib/include/nec7210.h
@@ -0,0 +1,141 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/***************************************************************************
+ *    copyright            : (C) 2002 by Frank Mori Hess
+ ***************************************************************************/
+
+#ifndef _NEC7210_H
+#define _NEC7210_H
+
+#include "gpib_state_machines.h"
+#include <linux/types.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/interrupt.h>
+
+#include "gpib_types.h"
+#include "nec7210_registers.h"
+
+/* struct used to provide variables local to a nec7210 chip */
+struct nec7210_priv {
+#ifdef CONFIG_HAS_IOPORT
+	u32 iobase;
+#endif
+	void __iomem *mmiobase;
+	unsigned int offset;		// offset between successive nec7210 io addresses
+	unsigned int dma_channel;
+	u8 *dma_buffer;
+	unsigned int dma_buffer_length;	// length of dma buffer
+	dma_addr_t dma_buffer_addr;	// bus address of board->buffer for use with dma
+	// software copy of bits written to registers
+	u8 reg_bits[8];
+	u8 auxa_bits;			// bits written to auxiliary register A
+	u8 auxb_bits;			// bits written to auxiliary register B
+	// used to keep track of board's state, bit definitions given below
+	unsigned long state;
+	// lock for chips that extend the nec7210 registers by paging in alternate regs
+	spinlock_t register_page_lock;
+	// wrappers for outb, inb, readb, or writeb
+	u8 (*read_byte)(struct nec7210_priv *priv, unsigned int register_number);
+	void (*write_byte)(struct nec7210_priv *priv, u8 byte, unsigned int register_number);
+	enum nec7210_chipset type;
+	enum talker_function_state talker_state;
+	enum listener_function_state listener_state;
+	void *private;
+	unsigned srq_pending : 1;
+};
+
+static inline void init_nec7210_private(struct nec7210_priv *priv)
+{
+	memset(priv, 0, sizeof(struct nec7210_priv));
+	spin_lock_init(&priv->register_page_lock);
+}
+
+// slightly shorter way to access read_byte and write_byte
+static inline u8 read_byte(struct nec7210_priv *priv, unsigned int register_number)
+{
+	return priv->read_byte(priv, register_number);
+}
+
+static inline void write_byte(struct nec7210_priv *priv, u8 byte, unsigned int register_number)
+{
+	priv->write_byte(priv, byte, register_number);
+}
+
+// struct nec7210_priv.state bit numbers
+enum {
+	PIO_IN_PROGRESS_BN,		// pio transfer in progress
+	DMA_READ_IN_PROGRESS_BN,	// dma read transfer in progress
+	DMA_WRITE_IN_PROGRESS_BN,	// dma write transfer in progress
+	READ_READY_BN,			// board has data byte available to read
+	WRITE_READY_BN,			// board is ready to send a data byte
+	COMMAND_READY_BN,		// board is ready to send a command byte
+	RECEIVED_END_BN,		// received END
+	BUS_ERROR_BN,			// output error has occurred
+	RFD_HOLDOFF_BN,			// rfd holdoff in effect
+	DEV_CLEAR_BN,			// device clear received
+	ADR_CHANGE_BN,			// address state change occurred
+};
+
+// interface functions
+int nec7210_read(struct gpib_board *board, struct nec7210_priv *priv, u8 *buffer,
+		 size_t length, int *end, size_t *bytes_read);
+int nec7210_write(struct gpib_board *board, struct nec7210_priv *priv, u8 *buffer,
+		  size_t length, int send_eoi, size_t *bytes_written);
+int nec7210_command(struct gpib_board *board, struct nec7210_priv *priv, u8 *buffer,
+		    size_t length, size_t *bytes_written);
+int nec7210_take_control(struct gpib_board *board, struct nec7210_priv *priv, int syncronous);
+int nec7210_go_to_standby(struct gpib_board *board, struct nec7210_priv *priv);
+int nec7210_request_system_control(struct gpib_board *board,
+				   struct nec7210_priv *priv, int request_control);
+void nec7210_interface_clear(struct gpib_board *board, struct nec7210_priv *priv, int assert);
+void nec7210_remote_enable(struct gpib_board *board, struct nec7210_priv *priv, int enable);
+int nec7210_enable_eos(struct gpib_board *board, struct nec7210_priv *priv, u8 eos_bytes,
+		       int compare_8_bits);
+void nec7210_disable_eos(struct gpib_board *board, struct nec7210_priv *priv);
+unsigned int nec7210_update_status(struct gpib_board *board, struct nec7210_priv *priv,
+				   unsigned int clear_mask);
+unsigned int nec7210_update_status_nolock(struct gpib_board *board, struct nec7210_priv *priv);
+int nec7210_primary_address(const struct gpib_board *board,
+			    struct nec7210_priv *priv, unsigned int address);
+int nec7210_secondary_address(const struct gpib_board *board, struct nec7210_priv *priv,
+			      unsigned int address, int enable);
+int nec7210_parallel_poll(struct gpib_board *board, struct nec7210_priv *priv, u8 *result);
+void nec7210_serial_poll_response(struct gpib_board *board,
+				  struct nec7210_priv *priv, u8 status);
+void nec7210_parallel_poll_configure(struct gpib_board *board,
+				     struct nec7210_priv *priv, unsigned int configuration);
+void nec7210_parallel_poll_response(struct gpib_board *board,
+				    struct nec7210_priv *priv, int ist);
+u8 nec7210_serial_poll_status(struct gpib_board *board, struct nec7210_priv *priv);
+int nec7210_t1_delay(struct gpib_board *board,
+		     struct nec7210_priv *priv, unsigned int nano_sec);
+void nec7210_return_to_local(const struct gpib_board *board, struct nec7210_priv *priv);
+
+// utility functions
+void nec7210_board_reset(struct nec7210_priv *priv, const struct gpib_board *board);
+void nec7210_board_online(struct nec7210_priv *priv, const struct gpib_board *board);
+unsigned int nec7210_set_reg_bits(struct nec7210_priv *priv, unsigned int reg,
+				  unsigned int mask, unsigned int bits);
+void nec7210_set_handshake_mode(struct gpib_board *board, struct nec7210_priv *priv, int mode);
+void nec7210_release_rfd_holdoff(struct gpib_board *board, struct nec7210_priv *priv);
+u8 nec7210_read_data_in(struct gpib_board *board, struct nec7210_priv *priv, int *end);
+
+// wrappers for io functions
+u8 nec7210_ioport_read_byte(struct nec7210_priv *priv, unsigned int register_num);
+void nec7210_ioport_write_byte(struct nec7210_priv *priv, u8 data, unsigned int register_num);
+u8 nec7210_iomem_read_byte(struct nec7210_priv *priv, unsigned int register_num);
+void nec7210_iomem_write_byte(struct nec7210_priv *priv, u8 data, unsigned int register_num);
+u8 nec7210_locking_ioport_read_byte(struct nec7210_priv *priv, unsigned int register_num);
+void nec7210_locking_ioport_write_byte(struct nec7210_priv *priv, u8 data,
+				       unsigned int register_num);
+u8 nec7210_locking_iomem_read_byte(struct nec7210_priv *priv, unsigned int register_num);
+void nec7210_locking_iomem_write_byte(struct nec7210_priv *priv, u8 data,
+				      unsigned int register_num);
+
+// interrupt service routine
+irqreturn_t nec7210_interrupt(struct gpib_board *board, struct nec7210_priv *priv);
+irqreturn_t nec7210_interrupt_have_status(struct gpib_board *board,
+					  struct nec7210_priv *priv, int status1, int status2);
+
+#endif	//_NEC7210_H