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, 195 insertions, 0 deletions

diff --git a/drivers/acpi/evged.c b/drivers/acpi/evged.c
new file mode 100644
index 000000000..5c35cbc7f
--- /dev/null
+++ b/drivers/acpi/evged.c
@@ -0,0 +1,195 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Generic Event Device for ACPI.
+ *
+ * Copyright (c) 2016, The Linux Foundation. All rights reserved.
+ *
+ * Generic Event Device allows platforms to handle interrupts in ACPI
+ * ASL statements. It follows very similar to  _EVT method approach
+ * from GPIO events. All interrupts are listed in _CRS and the handler
+ * is written in _EVT method. Here is an example.
+ *
+ * Device (GED0)
+ * {
+ *
+ *     Name (_HID, "ACPI0013")
+ *     Name (_UID, 0)
+ *     Method (_CRS, 0x0, Serialized)
+ *     {
+ *		Name (RBUF, ResourceTemplate ()
+ *		{
+ *		Interrupt(ResourceConsumer, Edge, ActiveHigh, Shared, , , )
+ *		{123}
+ *		}
+ *     })
+ *
+ *     Method (_EVT, 1) {
+ *             if (Lequal(123, Arg0))
+ *             {
+ *             }
+ *     }
+ * }
+ */
+
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/list.h>
+#include <linux/platform_device.h>
+#include <linux/acpi.h>
+
+#define MODULE_NAME	"acpi-ged"
+
+struct acpi_ged_device {
+	struct device *dev;
+	struct list_head event_list;
+};
+
+struct acpi_ged_event {
+	struct list_head node;
+	struct device *dev;
+	unsigned int gsi;
+	unsigned int irq;
+	acpi_handle handle;
+};
+
+static irqreturn_t acpi_ged_irq_handler(int irq, void *data)
+{
+	struct acpi_ged_event *event = data;
+	acpi_status acpi_ret;
+
+	acpi_ret = acpi_execute_simple_method(event->handle, NULL, event->gsi);
+	if (ACPI_FAILURE(acpi_ret))
+		dev_err_once(event->dev, "IRQ method execution failed\n");
+
+	return IRQ_HANDLED;
+}
+
+static acpi_status acpi_ged_request_interrupt(struct acpi_resource *ares,
+					      void *context)
+{
+	struct acpi_ged_event *event;
+	unsigned int irq;
+	unsigned int gsi;
+	unsigned int irqflags = IRQF_ONESHOT;
+	struct acpi_ged_device *geddev = context;
+	struct device *dev = geddev->dev;
+	acpi_handle handle = ACPI_HANDLE(dev);
+	acpi_handle evt_handle;
+	struct resource r;
+	struct acpi_resource_irq *p = &ares->data.irq;
+	struct acpi_resource_extended_irq *pext = &ares->data.extended_irq;
+	char ev_name[5];
+	u8 trigger;
+
+	if (ares->type == ACPI_RESOURCE_TYPE_END_TAG)
+		return AE_OK;
+
+	if (!acpi_dev_resource_interrupt(ares, 0, &r)) {
+		dev_err(dev, "unable to parse IRQ resource\n");
+		return AE_ERROR;
+	}
+	if (ares->type == ACPI_RESOURCE_TYPE_IRQ) {
+		gsi = p->interrupts[0];
+		trigger = p->triggering;
+	} else {
+		gsi = pext->interrupts[0];
+		trigger = pext->triggering;
+	}
+
+	irq = r.start;
+
+	switch (gsi) {
+	case 0 ... 255:
+		sprintf(ev_name, "_%c%02X",
+			trigger == ACPI_EDGE_SENSITIVE ? 'E' : 'L', gsi);
+
+		if (ACPI_SUCCESS(acpi_get_handle(handle, ev_name, &evt_handle)))
+			break;
+		fallthrough;
+	default:
+		if (ACPI_SUCCESS(acpi_get_handle(handle, "_EVT", &evt_handle)))
+			break;
+
+		dev_err(dev, "cannot locate _EVT method\n");
+		return AE_ERROR;
+	}
+
+	event = devm_kzalloc(dev, sizeof(*event), GFP_KERNEL);
+	if (!event)
+		return AE_ERROR;
+
+	event->gsi = gsi;
+	event->dev = dev;
+	event->irq = irq;
+	event->handle = evt_handle;
+
+	if (r.flags & IORESOURCE_IRQ_SHAREABLE)
+		irqflags |= IRQF_SHARED;
+
+	if (request_threaded_irq(irq, NULL, acpi_ged_irq_handler,
+				 irqflags, "ACPI:Ged", event)) {
+		dev_err(dev, "failed to setup event handler for irq %u\n", irq);
+		return AE_ERROR;
+	}
+
+	dev_dbg(dev, "GED listening GSI %u @ IRQ %u\n", gsi, irq);
+	list_add_tail(&event->node, &geddev->event_list);
+	return AE_OK;
+}
+
+static int ged_probe(struct platform_device *pdev)
+{
+	struct acpi_ged_device *geddev;
+	acpi_status acpi_ret;
+
+	geddev = devm_kzalloc(&pdev->dev, sizeof(*geddev), GFP_KERNEL);
+	if (!geddev)
+		return -ENOMEM;
+
+	geddev->dev = &pdev->dev;
+	INIT_LIST_HEAD(&geddev->event_list);
+	acpi_ret = acpi_walk_resources(ACPI_HANDLE(&pdev->dev), "_CRS",
+				       acpi_ged_request_interrupt, geddev);
+	if (ACPI_FAILURE(acpi_ret)) {
+		dev_err(&pdev->dev, "unable to parse the _CRS record\n");
+		return -EINVAL;
+	}
+	platform_set_drvdata(pdev, geddev);
+
+	return 0;
+}
+
+static void ged_shutdown(struct platform_device *pdev)
+{
+	struct acpi_ged_device *geddev = platform_get_drvdata(pdev);
+	struct acpi_ged_event *event, *next;
+
+	list_for_each_entry_safe(event, next, &geddev->event_list, node) {
+		free_irq(event->irq, event);
+		list_del(&event->node);
+		dev_dbg(geddev->dev, "GED releasing GSI %u @ IRQ %u\n",
+			 event->gsi, event->irq);
+	}
+}
+
+static void ged_remove(struct platform_device *pdev)
+{
+	ged_shutdown(pdev);
+}
+
+static const struct acpi_device_id ged_acpi_ids[] = {
+	{"ACPI0013"},
+	{},
+};
+
+static struct platform_driver ged_driver = {
+	.probe = ged_probe,
+	.remove = ged_remove,
+	.shutdown = ged_shutdown,
+	.driver = {
+		.name = MODULE_NAME,
+		.acpi_match_table = ACPI_PTR(ged_acpi_ids),
+	},
+};
+builtin_platform_driver(ged_driver);