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, 716 insertions, 0 deletions

diff --git a/drivers/gpib/common/iblib.c b/drivers/gpib/common/iblib.c
new file mode 100644
index 000000000..b672dd6aa
--- /dev/null
+++ b/drivers/gpib/common/iblib.c
@@ -0,0 +1,716 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/***************************************************************************
+ *    copyright            : (C) 2001, 2002 by Frank Mori Hess
+ ***************************************************************************/
+
+#define dev_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include "ibsys.h"
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/vmalloc.h>
+
+/*
+ * IBCAC
+ * Return to the controller active state from the
+ * controller standby state, i.e., turn ATN on.  Note
+ * that in order to enter the controller active state
+ * from the controller idle state, ibsic must be called.
+ * If sync is non-zero, attempt to take control synchronously.
+ * If fallback_to_async is non-zero, try to take control asynchronously
+ * if synchronous attempt fails.
+ */
+int ibcac(struct gpib_board *board, int sync, int fallback_to_async)
+{
+	int status = ibstatus(board);
+	int retval;
+
+	if ((status & CIC) == 0)
+		return -EINVAL;
+
+	if (status & ATN)
+		return 0;
+
+	if (sync && (status & LACS) == 0)
+		/*
+		 * tcs (take control synchronously) can only possibly work when
+		 * controller is listener.  Error code also needs to be -ETIMEDOUT
+		 * or it will giveout without doing fallback.
+		 */
+		retval = -ETIMEDOUT;
+	else
+		retval = board->interface->take_control(board, sync);
+
+	if (retval < 0 && fallback_to_async) {
+		if (sync && retval == -ETIMEDOUT)
+			retval = board->interface->take_control(board, 0);
+	}
+	board->interface->update_status(board, 0);
+
+	return retval;
+}
+
+/*
+ * After ATN is asserted, it should cause any connected devices
+ * to start listening for command bytes and leave acceptor idle state.
+ * So if ATN is asserted and neither NDAC or NRFD are asserted,
+ * then there are no devices and ibcmd should error out immediately.
+ * Some gpib hardware sees itself asserting NDAC/NRFD when it
+ * is controller in charge, in which case this check will
+ * do nothing useful (but shouldn't cause any harm either).
+ * Drivers that don't need this check (ni_usb for example) may
+ * set the skip_check_for_command_acceptors flag in their
+ * gpib_interface_struct to avoid useless overhead.
+ */
+static int check_for_command_acceptors(struct gpib_board *board)
+{
+	int lines;
+
+	if (board->interface->skip_check_for_command_acceptors)
+		return 0;
+	if (!board->interface->line_status)
+		return 0;
+
+	udelay(2); // allow time for devices to respond to ATN if it was just asserted
+
+	lines = board->interface->line_status(board);
+	if (lines < 0)
+		return lines;
+
+	if ((lines & VALID_NRFD) && (lines & VALID_NDAC))	{
+		if ((lines & BUS_NRFD) == 0 && (lines & BUS_NDAC) == 0)
+			return -ENOTCONN;
+	}
+
+	return 0;
+}
+
+/*
+ * IBCMD
+ * Write cnt command bytes from buf to the GPIB.  The
+ * command operation terminates only on I/O complete.
+ *
+ * NOTE:
+ *      1.  Prior to beginning the command, the interface is
+ *          placed in the controller active state.
+ *      2.  Before calling ibcmd for the first time, ibsic
+ *          must be called to initialize the GPIB and enable
+ *          the interface to leave the controller idle state.
+ */
+int ibcmd(struct gpib_board *board, u8 *buf, size_t length, size_t *bytes_written)
+{
+	ssize_t ret = 0;
+	int status;
+
+	*bytes_written = 0;
+
+	status = ibstatus(board);
+
+	if ((status & CIC) == 0)
+		return -EINVAL;
+
+	os_start_timer(board, board->usec_timeout);
+
+	ret = ibcac(board, 1, 1);
+	if (ret == 0) {
+		ret = check_for_command_acceptors(board);
+		if (ret == 0)
+			ret = board->interface->command(board, buf, length, bytes_written);
+	}
+
+	os_remove_timer(board);
+
+	if (io_timed_out(board))
+		ret = -ETIMEDOUT;
+
+	return ret;
+}
+
+/*
+ * IBGTS
+ * Go to the controller standby state from the controller
+ * active state, i.e., turn ATN off.
+ */
+
+int ibgts(struct gpib_board *board)
+{
+	int status = ibstatus(board);
+	int retval;
+
+	if ((status & CIC) == 0)
+		return -EINVAL;
+
+	retval = board->interface->go_to_standby(board);    /* go to standby */
+
+	board->interface->update_status(board, 0);
+
+	return retval;
+}
+
+static int autospoll_wait_should_wake_up(struct gpib_board *board)
+{
+	int retval;
+
+	mutex_lock(&board->big_gpib_mutex);
+
+	retval = board->master && board->autospollers > 0 &&
+		!atomic_read(&board->stuck_srq) &&
+		test_and_clear_bit(SRQI_NUM, &board->status);
+
+	mutex_unlock(&board->big_gpib_mutex);
+	return retval;
+}
+
+static int autospoll_thread(void *board_void)
+{
+	struct gpib_board *board = board_void;
+	int retval = 0;
+
+	dev_dbg(board->gpib_dev, "entering autospoll thread\n");
+
+	while (1) {
+		wait_event_interruptible(board->wait,
+					 kthread_should_stop() ||
+					 autospoll_wait_should_wake_up(board));
+		dev_dbg(board->gpib_dev, "autospoll wait satisfied\n");
+		if (kthread_should_stop())
+			break;
+
+		mutex_lock(&board->big_gpib_mutex);
+		/* make sure we are still good after we have lock */
+		if (board->autospollers <= 0 || board->master == 0) {
+			mutex_unlock(&board->big_gpib_mutex);
+			continue;
+		}
+		mutex_unlock(&board->big_gpib_mutex);
+
+		if (try_module_get(board->provider_module)) {
+			retval = autopoll_all_devices(board);
+			module_put(board->provider_module);
+		} else {
+			dev_err(board->gpib_dev, "try_module_get() failed!\n");
+		}
+		if (retval <= 0) {
+			dev_err(board->gpib_dev, "stuck SRQ\n");
+
+			atomic_set(&board->stuck_srq, 1);	// XXX could be better
+			set_bit(SRQI_NUM, &board->status);
+		}
+	}
+	return retval;
+}
+
+int ibonline(struct gpib_board *board)
+{
+	int retval;
+
+	if (board->online)
+		return -EBUSY;
+	if (!board->interface)
+		return -ENODEV;
+	retval = gpib_allocate_board(board);
+	if (retval < 0)
+		return retval;
+
+	board->dev = NULL;
+	board->local_ppoll_mode = 0;
+	retval = board->interface->attach(board, &board->config);
+	if (retval < 0) {
+		board->interface->detach(board);
+		return retval;
+	}
+	/*
+	 * nios2nommu on 2.6.11 uclinux kernel has weird problems
+	 * with autospoll thread causing huge slowdowns
+	 */
+#ifndef CONFIG_NIOS2
+	board->autospoll_task = kthread_run(&autospoll_thread, board,
+					    "gpib%d_autospoll_kthread", board->minor);
+	if (IS_ERR(board->autospoll_task)) {
+		dev_err(board->gpib_dev, "failed to create autospoll thread\n");
+		board->interface->detach(board);
+		return PTR_ERR(board->autospoll_task);
+	}
+#endif
+	board->online = 1;
+	dev_dbg(board->gpib_dev, "board online\n");
+
+	return 0;
+}
+
+/* XXX need to make sure board is generally not in use (grab board lock?) */
+int iboffline(struct gpib_board *board)
+{
+	int retval;
+
+	if (board->online == 0)
+		return 0;
+	if (!board->interface)
+		return -ENODEV;
+
+	if (board->autospoll_task && !IS_ERR(board->autospoll_task)) {
+		retval = kthread_stop(board->autospoll_task);
+		if (retval)
+			dev_err(board->gpib_dev, "kthread_stop returned %i\n", retval);
+		board->autospoll_task = NULL;
+	}
+
+	board->interface->detach(board);
+	gpib_deallocate_board(board);
+	board->online = 0;
+	dev_dbg(board->gpib_dev, "board offline\n");
+
+	return 0;
+}
+
+/*
+ * IBLINES
+ * Poll the GPIB control lines and return their status in buf.
+ *
+ *      LSB (bits 0-7)  -  VALID lines mask (lines that can be monitored).
+ * Next LSB (bits 8-15) - STATUS lines mask (lines that are currently set).
+ *
+ */
+int iblines(const struct gpib_board *board, short *lines)
+{
+	int retval;
+
+	*lines = 0;
+	if (!board->interface->line_status)
+		return 0;
+	retval = board->interface->line_status(board);
+	if (retval < 0)
+		return retval;
+	*lines = retval;
+	return 0;
+}
+
+/*
+ * IBRD
+ * Read up to 'length' bytes of data from the GPIB into buf.  End
+ * on detection of END (EOI and or EOS) and set 'end_flag'.
+ *
+ * NOTE:
+ *      1.  The interface is placed in the controller standby
+ *          state prior to beginning the read.
+ *      2.  Prior to calling ibrd, the intended devices as well
+ *          as the interface board itself must be addressed by
+ *          calling ibcmd.
+ */
+
+int ibrd(struct gpib_board *board, u8 *buf, size_t length, int *end_flag, size_t *nbytes)
+{
+	ssize_t ret = 0;
+	int retval;
+	size_t bytes_read;
+
+	*nbytes = 0;
+	*end_flag = 0;
+	if (length == 0)
+		return 0;
+
+	if (board->master) {
+		retval = ibgts(board);
+		if (retval < 0)
+			return retval;
+	}
+	/*
+	 * XXX resetting timer here could cause timeouts take longer than they should,
+	 * since read_ioctl calls this
+	 * function in a loop, there is probably a similar problem with writes/commands
+	 */
+	os_start_timer(board, board->usec_timeout);
+
+	do {
+		ret = board->interface->read(board, buf, length - *nbytes, end_flag, &bytes_read);
+		if (ret < 0)
+			goto ibrd_out;
+
+		buf += bytes_read;
+		*nbytes += bytes_read;
+		if (need_resched())
+			schedule();
+	} while (ret == 0 && *nbytes > 0 && *nbytes < length && *end_flag == 0);
+ibrd_out:
+	os_remove_timer(board);
+
+	return ret;
+}
+
+/*
+ * IBRPP
+ * Conduct a parallel poll and return the byte in buf.
+ *
+ * NOTE:
+ *	1.  Prior to conducting the poll the interface is placed
+ *	    in the controller active state.
+ */
+int ibrpp(struct gpib_board *board, u8 *result)
+{
+	int retval = 0;
+
+	os_start_timer(board, board->usec_timeout);
+	retval = ibcac(board, 1, 1);
+	if (retval)
+		return -1;
+
+	retval =  board->interface->parallel_poll(board, result);
+
+	os_remove_timer(board);
+	return retval;
+}
+
+int ibppc(struct gpib_board *board, u8 configuration)
+{
+	configuration &= 0x1f;
+	board->interface->parallel_poll_configure(board, configuration);
+	board->parallel_poll_configuration = configuration;
+
+	return 0;
+}
+
+int ibrsv2(struct gpib_board *board, u8 status_byte, int new_reason_for_service)
+{
+	int board_status = ibstatus(board);
+	const unsigned int MSS = status_byte & request_service_bit;
+
+	if ((board_status & CIC))
+		return -EINVAL;
+
+	if (MSS == 0 && new_reason_for_service)
+		return -EINVAL;
+
+	if (board->interface->serial_poll_response2)	{
+		board->interface->serial_poll_response2(board, status_byte, new_reason_for_service);
+		// fall back on simpler serial_poll_response if the behavior would be the same
+	} else if (board->interface->serial_poll_response &&
+		   (MSS == 0 || (MSS && new_reason_for_service))) {
+		board->interface->serial_poll_response(board, status_byte);
+	} else {
+		return -EOPNOTSUPP;
+	}
+
+	return 0;
+}
+
+/*
+ * IBSIC
+ * Send IFC for at least 100 microseconds.
+ *
+ * NOTE:
+ *	1.  Ibsic must be called prior to the first call to
+ *	    ibcmd in order to initialize the bus and enable the
+ *	    interface to leave the controller idle state.
+ */
+int ibsic(struct gpib_board *board, unsigned int usec_duration)
+{
+	if (board->master == 0)
+		return -EINVAL;
+
+	if (usec_duration < 100)
+		usec_duration = 100;
+	if (usec_duration > 1000)
+		usec_duration = 1000;
+
+	dev_dbg(board->gpib_dev, "sending interface clear, delay = %ius\n", usec_duration);
+	board->interface->interface_clear(board, 1);
+	udelay(usec_duration);
+	board->interface->interface_clear(board, 0);
+
+	return 0;
+}
+
+int ibrsc(struct gpib_board *board, int request_control)
+{
+	int retval;
+
+	if (!board->interface->request_system_control)
+		return -EPERM;
+
+	retval = board->interface->request_system_control(board, request_control);
+
+	if (retval)
+		return retval;
+
+	board->master = request_control != 0;
+
+	return  0;
+}
+
+/*
+ * IBSRE
+ * Send REN true if v is non-zero or false if v is zero.
+ */
+int ibsre(struct gpib_board *board, int enable)
+{
+	if (board->master == 0)
+		return -EINVAL;
+
+	board->interface->remote_enable(board, enable);	/* set or clear REN */
+	if (!enable)
+		usleep_range(100, 150);
+
+	return 0;
+}
+
+/*
+ * IBPAD
+ * change the GPIB address of the interface board.  The address
+ * must be 0 through 30.  ibonl resets the address to PAD.
+ */
+int ibpad(struct gpib_board *board, unsigned int addr)
+{
+	if (addr > MAX_GPIB_PRIMARY_ADDRESS)
+		return -EINVAL;
+
+	board->pad = addr;
+	if (board->online)
+		board->interface->primary_address(board, board->pad);
+	dev_dbg(board->gpib_dev, "set primary addr to %i\n", board->pad);
+	return 0;
+}
+
+/*
+ * IBSAD
+ * change the secondary GPIB address of the interface board.
+ * The address must be 0 through 30, or negative disables.  ibonl resets the
+ * address to SAD.
+ */
+int ibsad(struct gpib_board *board, int addr)
+{
+	if (addr > MAX_GPIB_SECONDARY_ADDRESS)
+		return -EINVAL;
+	board->sad = addr;
+	if (board->online) {
+		if (board->sad >= 0)
+			board->interface->secondary_address(board, board->sad, 1);
+		else
+			board->interface->secondary_address(board, 0, 0);
+	}
+	dev_dbg(board->gpib_dev, "set secondary addr to %i\n", board->sad);
+
+	return 0;
+}
+
+/*
+ * IBEOS
+ * Set the end-of-string modes for I/O operations to v.
+ *
+ */
+int ibeos(struct gpib_board *board, int eos, int eosflags)
+{
+	int retval;
+
+	if (eosflags & ~EOS_MASK)
+		return -EINVAL;
+	if (eosflags & REOS) {
+		retval = board->interface->enable_eos(board, eos, eosflags & BIN);
+	} else {
+		board->interface->disable_eos(board);
+		retval = 0;
+	}
+	return retval;
+}
+
+int ibstatus(struct gpib_board *board)
+{
+	return general_ibstatus(board, NULL, 0, 0, NULL);
+}
+
+int general_ibstatus(struct gpib_board *board, const struct gpib_status_queue *device,
+		     int clear_mask, int set_mask, struct gpib_descriptor *desc)
+{
+	int status = 0;
+	short line_status;
+
+	if (board->private_data) {
+		status = board->interface->update_status(board, clear_mask);
+		/*
+		 * XXX should probably stop having drivers use TIMO bit in
+		 * board->status to avoid confusion
+		 */
+		status &= ~TIMO;
+		/* get real SRQI status if we can */
+		if (iblines(board, &line_status) == 0) {
+			if ((line_status & VALID_SRQ)) {
+				if ((line_status & BUS_SRQ))
+					status |= SRQI;
+				else
+					status &= ~SRQI;
+			}
+		}
+	}
+	if (device)
+		if (num_status_bytes(device))
+			status |= RQS;
+
+	if (desc) {
+		if (set_mask & CMPL)
+			atomic_set(&desc->io_in_progress, 0);
+		else if (clear_mask & CMPL)
+			atomic_set(&desc->io_in_progress, 1);
+
+		if (atomic_read(&desc->io_in_progress))
+			status &= ~CMPL;
+		else
+			status |= CMPL;
+	}
+	if (num_gpib_events(&board->event_queue))
+		status |= EVENT;
+	else
+		status &= ~EVENT;
+
+	return status;
+}
+
+struct wait_info {
+	struct gpib_board *board;
+	struct timer_list timer;
+	int timed_out;
+	unsigned long usec_timeout;
+};
+
+static void wait_timeout(struct timer_list *t)
+{
+	struct wait_info *winfo = timer_container_of(winfo, t, timer);
+
+	winfo->timed_out = 1;
+	wake_up_interruptible(&winfo->board->wait);
+}
+
+static void init_wait_info(struct wait_info *winfo)
+{
+	winfo->board = NULL;
+	winfo->timed_out = 0;
+	timer_setup_on_stack(&winfo->timer, wait_timeout, 0);
+}
+
+static int wait_satisfied(struct wait_info *winfo, struct gpib_status_queue *status_queue,
+			  int wait_mask, int *status, struct gpib_descriptor *desc)
+{
+	struct gpib_board *board = winfo->board;
+	int temp_status;
+
+	if (mutex_lock_interruptible(&board->big_gpib_mutex))
+		return -ERESTARTSYS;
+
+	temp_status = general_ibstatus(board, status_queue, 0, 0, desc);
+
+	mutex_unlock(&board->big_gpib_mutex);
+
+	if (winfo->timed_out)
+		temp_status |= TIMO;
+	else
+		temp_status &= ~TIMO;
+	if (wait_mask & temp_status) {
+		*status = temp_status;
+		return 1;
+	}
+// XXX does wait for END work?
+	return 0;
+}
+
+/* install timer interrupt handler */
+static void start_wait_timer(struct wait_info *winfo)
+/* Starts the timeout task  */
+{
+	winfo->timed_out = 0;
+
+	if (winfo->usec_timeout > 0)
+		mod_timer(&winfo->timer, jiffies + usec_to_jiffies(winfo->usec_timeout));
+}
+
+static void remove_wait_timer(struct wait_info *winfo)
+{
+	timer_delete_sync(&winfo->timer);
+	timer_destroy_on_stack(&winfo->timer);
+}
+
+/*
+ * IBWAIT
+ * Check or wait for a GPIB event to occur.  The mask argument
+ * is a bit vector corresponding to the status bit vector.  It
+ * has a bit set for each condition which can terminate the wait
+ * If the mask is 0 then
+ * no condition is waited for.
+ */
+int ibwait(struct gpib_board *board, int wait_mask, int clear_mask, int set_mask,
+	   int *status, unsigned long usec_timeout, struct gpib_descriptor *desc)
+{
+	int retval = 0;
+	struct gpib_status_queue *status_queue;
+	struct wait_info winfo;
+
+	if (desc->is_board)
+		status_queue = NULL;
+	else
+		status_queue = get_gpib_status_queue(board, desc->pad, desc->sad);
+
+	if (wait_mask == 0) {
+		*status = general_ibstatus(board, status_queue, clear_mask, set_mask, desc);
+		return 0;
+	}
+
+	mutex_unlock(&board->big_gpib_mutex);
+
+	init_wait_info(&winfo);
+	winfo.board = board;
+	winfo.usec_timeout = usec_timeout;
+	start_wait_timer(&winfo);
+
+	if (wait_event_interruptible(board->wait, wait_satisfied(&winfo, status_queue,
+								 wait_mask, status, desc))) {
+		dev_dbg(board->gpib_dev, "wait interrupted\n");
+		retval = -ERESTARTSYS;
+	}
+	remove_wait_timer(&winfo);
+
+	if (retval)
+		return retval;
+	if (mutex_lock_interruptible(&board->big_gpib_mutex))
+		return -ERESTARTSYS;
+
+	/* make sure we only clear status bits that we are reporting */
+	if (*status & clear_mask || set_mask)
+		general_ibstatus(board, status_queue, *status & clear_mask, set_mask, NULL);
+
+	return 0;
+}
+
+/*
+ * IBWRT
+ * Write cnt bytes of data from buf to the GPIB.  The write
+ * operation terminates only on I/O complete.
+ *
+ * NOTE:
+ *      1.  Prior to beginning the write, the interface is
+ *          placed in the controller standby state.
+ *      2.  Prior to calling ibwrt, the intended devices as
+ *          well as the interface board itself must be
+ *          addressed by calling ibcmd.
+ */
+int ibwrt(struct gpib_board *board, u8 *buf, size_t cnt, int send_eoi, size_t *bytes_written)
+{
+	int ret = 0;
+	int retval;
+
+	if (cnt == 0)
+		return 0;
+
+	if (board->master) {
+		retval = ibgts(board);
+		if (retval < 0)
+			return retval;
+	}
+	os_start_timer(board, board->usec_timeout);
+	ret = board->interface->write(board, buf, cnt, send_eoi, bytes_written);
+
+	if (io_timed_out(board))
+		ret = -ETIMEDOUT;
+
+	os_remove_timer(board);
+
+	return ret;
+}
+