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, 224 insertions, 0 deletions

diff --git a/drivers/misc/ibmasm/module.c b/drivers/misc/ibmasm/module.c
new file mode 100644
index 000000000..4509c15a7
--- /dev/null
+++ b/drivers/misc/ibmasm/module.c
@@ -0,0 +1,224 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/*
+ * IBM ASM Service Processor Device Driver
+ *
+ * Copyright (C) IBM Corporation, 2004
+ *
+ * Author: Max Asböck <amax@us.ibm.com>
+ *
+ * This driver is based on code originally written by Pete Reynolds
+ * and others.
+ */
+
+/*
+ * The ASM device driver does the following things:
+ *
+ * 1) When loaded it sends a message to the service processor,
+ * indicating that an OS is * running. This causes the service processor
+ * to send periodic heartbeats to the OS.
+ *
+ * 2) Answers the periodic heartbeats sent by the service processor.
+ * Failure to do so would result in system reboot.
+ *
+ * 3) Acts as a pass through for dot commands sent from user applications.
+ * The interface for this is the ibmasmfs file system.
+ *
+ * 4) Allows user applications to register for event notification. Events
+ * are sent to the driver through interrupts. They can be read from user
+ * space through the ibmasmfs file system.
+ *
+ * 5) Allows user space applications to send heartbeats to the service
+ * processor (aka reverse heartbeats). Again this happens through ibmasmfs.
+ *
+ * 6) Handles remote mouse and keyboard event interrupts and makes them
+ * available to user applications through ibmasmfs.
+ *
+ */
+
+#include <linux/pci.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include "ibmasm.h"
+#include "lowlevel.h"
+#include "remote.h"
+
+int ibmasm_debug = 0;
+module_param(ibmasm_debug, int , S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(ibmasm_debug, " Set debug mode on or off");
+
+
+static int ibmasm_init_one(struct pci_dev *pdev, const struct pci_device_id *id)
+{
+	int result;
+	struct service_processor *sp;
+
+	if ((result = pci_enable_device(pdev))) {
+		dev_err(&pdev->dev, "Failed to enable PCI device\n");
+		return result;
+	}
+	if ((result = pci_request_regions(pdev, DRIVER_NAME))) {
+		dev_err(&pdev->dev, "Failed to allocate PCI resources\n");
+		goto error_resources;
+	}
+	/* vnc client won't work without bus-mastering */
+	pci_set_master(pdev);
+
+	sp = kzalloc_obj(struct service_processor);
+	if (sp == NULL) {
+		dev_err(&pdev->dev, "Failed to allocate memory\n");
+		result = -ENOMEM;
+		goto error_kmalloc;
+	}
+
+	spin_lock_init(&sp->lock);
+	INIT_LIST_HEAD(&sp->command_queue);
+
+	pci_set_drvdata(pdev, (void *)sp);
+	sp->dev = &pdev->dev;
+	sp->number = pdev->bus->number;
+	snprintf(sp->dirname, IBMASM_NAME_SIZE, "%d", sp->number);
+	snprintf(sp->devname, IBMASM_NAME_SIZE, "%s%d", DRIVER_NAME, sp->number);
+
+	result = ibmasm_event_buffer_init(sp);
+	if (result) {
+		dev_err(sp->dev, "Failed to allocate event buffer\n");
+		goto error_eventbuffer;
+	}
+
+	result = ibmasm_heartbeat_init(sp);
+	if (result) {
+		dev_err(sp->dev, "Failed to allocate heartbeat command\n");
+		goto error_heartbeat;
+	}
+
+	sp->irq = pdev->irq;
+	sp->base_address = pci_ioremap_bar(pdev, 0);
+	if (!sp->base_address) {
+		dev_err(sp->dev, "Failed to ioremap pci memory\n");
+		result =  -ENODEV;
+		goto error_ioremap;
+	}
+
+	result = request_irq(sp->irq, ibmasm_interrupt_handler, IRQF_SHARED, sp->devname, (void*)sp);
+	if (result) {
+		dev_err(sp->dev, "Failed to register interrupt handler\n");
+		goto error_request_irq;
+	}
+
+	enable_sp_interrupts(sp->base_address);
+
+	result = ibmasm_init_remote_input_dev(sp);
+	if (result) {
+		dev_err(sp->dev, "Failed to initialize remote queue\n");
+		goto error_init_remote;
+	}
+
+	result = ibmasm_send_driver_vpd(sp);
+	if (result) {
+		dev_err(sp->dev, "Failed to send driver VPD to service processor\n");
+		goto error_send_message;
+	}
+	result = ibmasm_send_os_state(sp, SYSTEM_STATE_OS_UP);
+	if (result) {
+		dev_err(sp->dev, "Failed to send OS state to service processor\n");
+		goto error_send_message;
+	}
+	ibmasmfs_add_sp(sp);
+
+	ibmasm_register_uart(sp);
+
+	return 0;
+
+error_send_message:
+	ibmasm_free_remote_input_dev(sp);
+error_init_remote:
+	disable_sp_interrupts(sp->base_address);
+	free_irq(sp->irq, (void *)sp);
+error_request_irq:
+	iounmap(sp->base_address);
+error_ioremap:
+	ibmasm_heartbeat_exit(sp);
+error_heartbeat:
+	ibmasm_event_buffer_exit(sp);
+error_eventbuffer:
+	kfree(sp);
+error_kmalloc:
+        pci_release_regions(pdev);
+error_resources:
+        pci_disable_device(pdev);
+
+	return result;
+}
+
+static void ibmasm_remove_one(struct pci_dev *pdev)
+{
+	struct service_processor *sp = pci_get_drvdata(pdev);
+
+	dbg("Unregistering UART\n");
+	ibmasm_unregister_uart(sp);
+	dbg("Sending OS down message\n");
+	if (ibmasm_send_os_state(sp, SYSTEM_STATE_OS_DOWN))
+		err("failed to get response to 'Send OS State' command\n");
+	dbg("Disabling heartbeats\n");
+	ibmasm_heartbeat_exit(sp);
+	dbg("Disabling interrupts\n");
+	disable_sp_interrupts(sp->base_address);
+	dbg("Freeing SP irq\n");
+	free_irq(sp->irq, (void *)sp);
+	dbg("Cleaning up\n");
+	ibmasm_free_remote_input_dev(sp);
+	iounmap(sp->base_address);
+	ibmasm_event_buffer_exit(sp);
+	kfree(sp);
+	pci_release_regions(pdev);
+	pci_disable_device(pdev);
+}
+
+static struct pci_device_id ibmasm_pci_table[] =
+{
+	{ PCI_DEVICE(VENDORID_IBM, DEVICEID_RSA) },
+	{},
+};
+
+static struct pci_driver ibmasm_driver = {
+	.name		= DRIVER_NAME,
+	.id_table	= ibmasm_pci_table,
+	.probe		= ibmasm_init_one,
+	.remove		= ibmasm_remove_one,
+};
+
+static void __exit ibmasm_exit (void)
+{
+	ibmasm_unregister_panic_notifier();
+	ibmasmfs_unregister();
+	pci_unregister_driver(&ibmasm_driver);
+	info(DRIVER_DESC " version " DRIVER_VERSION " unloaded");
+}
+
+static int __init ibmasm_init(void)
+{
+	int result = pci_register_driver(&ibmasm_driver);
+	if (result)
+		return result;
+
+	result = ibmasmfs_register();
+	if (result) {
+		pci_unregister_driver(&ibmasm_driver);
+		err("Failed to register ibmasmfs file system");
+		return result;
+	}
+
+	ibmasm_register_panic_notifier();
+	info(DRIVER_DESC " version " DRIVER_VERSION " loaded");
+	return 0;
+}
+
+module_init(ibmasm_init);
+module_exit(ibmasm_exit);
+
+MODULE_AUTHOR(DRIVER_AUTHOR);
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+MODULE_DEVICE_TABLE(pci, ibmasm_pci_table);
+