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>

4 files changed, 346 insertions, 0 deletions

diff --git a/arch/m68k/virt/Makefile b/arch/m68k/virt/Makefile
new file mode 100644
index 000000000..54b9b2866
--- /dev/null
+++ b/arch/m68k/virt/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Makefile for Linux arch/m68k/virt source directory
+#
+
+obj-y		:= config.o ints.o platform.o
diff --git a/arch/m68k/virt/config.c b/arch/m68k/virt/config.c
new file mode 100644
index 000000000..b338e2a8d
--- /dev/null
+++ b/arch/m68k/virt/config.c
@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/reboot.h>
+#include <linux/serial_core.h>
+#include <clocksource/timer-goldfish.h>
+
+#include <asm/bootinfo.h>
+#include <asm/bootinfo-virt.h>
+#include <asm/byteorder.h>
+#include <asm/machdep.h>
+#include <asm/virt.h>
+#include <asm/config.h>
+
+struct virt_booter_data virt_bi_data;
+
+static void virt_get_model(char *str)
+{
+	/* str is 80 characters long */
+	sprintf(str, "QEMU Virtual M68K Machine (%u.%u.%u)",
+		(u8)(virt_bi_data.qemu_version >> 24),
+		(u8)(virt_bi_data.qemu_version >> 16),
+		(u8)(virt_bi_data.qemu_version >> 8));
+}
+static void virt_reset(void)
+{
+	do_kernel_restart(NULL);
+}
+
+/*
+ * Parse a virtual-m68k-specific record in the bootinfo
+ */
+
+int __init virt_parse_bootinfo(const struct bi_record *record)
+{
+	int unknown = 0;
+	const void *data = record->data;
+
+	switch (be16_to_cpu(record->tag)) {
+	case BI_VIRT_QEMU_VERSION:
+		virt_bi_data.qemu_version = be32_to_cpup(data);
+		break;
+	case BI_VIRT_GF_PIC_BASE:
+		virt_bi_data.pic.mmio = be32_to_cpup(data);
+		data += 4;
+		virt_bi_data.pic.irq = be32_to_cpup(data);
+		break;
+	case BI_VIRT_GF_RTC_BASE:
+		virt_bi_data.rtc.mmio = be32_to_cpup(data);
+		data += 4;
+		virt_bi_data.rtc.irq = be32_to_cpup(data);
+		break;
+	case BI_VIRT_GF_TTY_BASE:
+		virt_bi_data.tty.mmio = be32_to_cpup(data);
+		data += 4;
+		virt_bi_data.tty.irq = be32_to_cpup(data);
+		break;
+	case BI_VIRT_CTRL_BASE:
+		virt_bi_data.ctrl.mmio = be32_to_cpup(data);
+		data += 4;
+		virt_bi_data.ctrl.irq = be32_to_cpup(data);
+		break;
+	case BI_VIRT_VIRTIO_BASE:
+		virt_bi_data.virtio.mmio = be32_to_cpup(data);
+		data += 4;
+		virt_bi_data.virtio.irq = be32_to_cpup(data);
+		break;
+	default:
+		unknown = 1;
+		break;
+	}
+	return unknown;
+}
+
+static void __init virt_sched_init(void)
+{
+	goldfish_timer_init(virt_bi_data.rtc.irq,
+			    (void __iomem *)virt_bi_data.rtc.mmio);
+}
+
+void __init config_virt(void)
+{
+	char earlycon[24];
+
+	snprintf(earlycon, sizeof(earlycon), "early_gf_tty,0x%08x",
+		 virt_bi_data.tty.mmio);
+	setup_earlycon(earlycon);
+
+	mach_init_IRQ = virt_init_IRQ;
+	mach_sched_init = virt_sched_init;
+	mach_get_model = virt_get_model;
+	mach_reset = virt_reset;
+}
diff --git a/arch/m68k/virt/ints.c b/arch/m68k/virt/ints.c
new file mode 100644
index 000000000..896aa6eb8
--- /dev/null
+++ b/arch/m68k/virt/ints.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/sched/debug.h>
+#include <linux/types.h>
+#include <linux/ioport.h>
+
+#include <asm/hwtest.h>
+#include <asm/irq.h>
+#include <asm/irq_regs.h>
+#include <asm/processor.h>
+#include <asm/virt.h>
+
+#define GFPIC_REG_IRQ_PENDING           0x04
+#define GFPIC_REG_IRQ_DISABLE_ALL       0x08
+#define GFPIC_REG_IRQ_DISABLE           0x0c
+#define GFPIC_REG_IRQ_ENABLE            0x10
+
+static struct resource picres[6];
+static const char *picname[6] = {
+	"goldfish_pic.0",
+	"goldfish_pic.1",
+	"goldfish_pic.2",
+	"goldfish_pic.3",
+	"goldfish_pic.4",
+	"goldfish_pic.5"
+};
+
+/*
+ * 6 goldfish-pic for CPU IRQ #1 to IRQ #6
+ * CPU IRQ #1 -> PIC #1
+ *               IRQ #1 to IRQ #31 -> unused
+ *               IRQ #32 -> goldfish-tty
+ * CPU IRQ #2 -> PIC #2
+ *               IRQ #1 to IRQ #32 -> virtio-mmio from 1 to 32
+ * CPU IRQ #3 -> PIC #3
+ *               IRQ #1 to IRQ #32 -> virtio-mmio from 33 to 64
+ * CPU IRQ #4 -> PIC #4
+ *               IRQ #1 to IRQ #32 -> virtio-mmio from 65 to 96
+ * CPU IRQ #5 -> PIC #5
+ *               IRQ #1 to IRQ #32 -> virtio-mmio from 97 to 128
+ * CPU IRQ #6 -> PIC #6
+ *               IRQ #1 -> goldfish-timer
+ *               IRQ #2 -> goldfish-rtc
+ *               IRQ #3 to IRQ #32 -> unused
+ * CPU IRQ #7 -> NMI
+ */
+
+static u32 gfpic_read(int pic, int reg)
+{
+	void __iomem *base = (void __iomem *)(virt_bi_data.pic.mmio +
+					      pic * 0x1000);
+
+	return ioread32be(base + reg);
+}
+
+static void gfpic_write(u32 value, int pic, int reg)
+{
+	void __iomem *base = (void __iomem *)(virt_bi_data.pic.mmio +
+					      pic * 0x1000);
+
+	iowrite32be(value, base + reg);
+}
+
+#define GF_PIC(irq) ((irq - IRQ_USER) / 32)
+#define GF_IRQ(irq) ((irq - IRQ_USER) % 32)
+
+static void virt_irq_enable(struct irq_data *data)
+{
+	gfpic_write(BIT(GF_IRQ(data->irq)), GF_PIC(data->irq),
+		    GFPIC_REG_IRQ_ENABLE);
+}
+
+static void virt_irq_disable(struct irq_data *data)
+{
+	gfpic_write(BIT(GF_IRQ(data->irq)), GF_PIC(data->irq),
+		    GFPIC_REG_IRQ_DISABLE);
+}
+
+static unsigned int virt_irq_startup(struct irq_data *data)
+{
+	virt_irq_enable(data);
+	return 0;
+}
+
+static irqreturn_t virt_nmi_handler(int irq, void *dev_id)
+{
+	static int in_nmi;
+
+	if (READ_ONCE(in_nmi))
+		return IRQ_HANDLED;
+	WRITE_ONCE(in_nmi, 1);
+
+	pr_warn("Non-Maskable Interrupt\n");
+	show_registers(get_irq_regs());
+
+	WRITE_ONCE(in_nmi, 0);
+	return IRQ_HANDLED;
+}
+
+static struct irq_chip virt_irq_chip = {
+	.name		= "virt",
+	.irq_enable	= virt_irq_enable,
+	.irq_disable	= virt_irq_disable,
+	.irq_startup	= virt_irq_startup,
+	.irq_shutdown	= virt_irq_disable,
+};
+
+static void goldfish_pic_irq(struct irq_desc *desc)
+{
+	u32 irq_pending;
+	unsigned int irq_num;
+	unsigned int pic = desc->irq_data.irq - 1;
+
+	irq_pending = gfpic_read(pic, GFPIC_REG_IRQ_PENDING);
+	irq_num = IRQ_USER + pic * 32;
+
+	do {
+		if (irq_pending & 1)
+			generic_handle_irq(irq_num);
+		++irq_num;
+		irq_pending >>= 1;
+	} while (irq_pending);
+}
+
+void __init virt_init_IRQ(void)
+{
+	unsigned int i;
+
+	m68k_setup_irq_controller(&virt_irq_chip, handle_simple_irq, IRQ_USER,
+				  NUM_VIRT_SOURCES - IRQ_USER);
+
+	for (i = 0; i < 6; i++) {
+
+		picres[i] = (struct resource)
+		    DEFINE_RES_MEM_NAMED(virt_bi_data.pic.mmio + i * 0x1000,
+					 0x1000, picname[i]);
+		if (request_resource(&iomem_resource, &picres[i])) {
+			pr_err("Cannot allocate %s resource\n", picname[i]);
+			return;
+		}
+
+		irq_set_chained_handler(virt_bi_data.pic.irq + i,
+					goldfish_pic_irq);
+	}
+
+	if (request_irq(IRQ_AUTO_7, virt_nmi_handler, 0, "NMI",
+			virt_nmi_handler))
+		pr_err("Couldn't register NMI\n");
+}
diff --git a/arch/m68k/virt/platform.c b/arch/m68k/virt/platform.c
new file mode 100644
index 000000000..764f556b4
--- /dev/null
+++ b/arch/m68k/virt/platform.c
@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/platform_device.h>
+#include <linux/interrupt.h>
+#include <linux/memblock.h>
+#include <asm/virt.h>
+#include <asm/irq.h>
+
+#define VIRTIO_BUS_NB	128
+
+static struct platform_device * __init virt_virtio_init(unsigned int id)
+{
+	const struct resource res[] = {
+		DEFINE_RES_MEM(virt_bi_data.virtio.mmio + id * 0x200, 0x200),
+		DEFINE_RES_IRQ(virt_bi_data.virtio.irq + id),
+	};
+
+	return platform_device_register_simple("virtio-mmio", id,
+					       res, ARRAY_SIZE(res));
+}
+
+static int __init virt_platform_init(void)
+{
+	const struct resource goldfish_tty_res[] = {
+		DEFINE_RES_MEM(virt_bi_data.tty.mmio, 1),
+		DEFINE_RES_IRQ(virt_bi_data.tty.irq),
+	};
+	/* this is the second gf-rtc, the first one is used by the scheduler */
+	const struct resource goldfish_rtc_res[] = {
+		DEFINE_RES_MEM(virt_bi_data.rtc.mmio + 0x1000, 0x1000),
+		DEFINE_RES_IRQ(virt_bi_data.rtc.irq + 1),
+	};
+	const struct resource virt_ctrl_res[] = {
+		DEFINE_RES_MEM(virt_bi_data.ctrl.mmio, 0x100),
+	};
+	struct platform_device *pdev1, *pdev2, *pdev3;
+	struct platform_device *pdevs[VIRTIO_BUS_NB];
+	unsigned int i;
+	int ret = 0;
+
+	if (!MACH_IS_VIRT)
+		return -ENODEV;
+
+	/* We need this to have DMA'able memory provided to goldfish-tty */
+	min_low_pfn = 0;
+
+	pdev1 = platform_device_register_simple("goldfish_tty",
+						PLATFORM_DEVID_NONE,
+						goldfish_tty_res,
+						ARRAY_SIZE(goldfish_tty_res));
+	if (IS_ERR(pdev1))
+		return PTR_ERR(pdev1);
+
+	pdev2 = platform_device_register_simple("goldfish_rtc",
+						PLATFORM_DEVID_NONE,
+						goldfish_rtc_res,
+						ARRAY_SIZE(goldfish_rtc_res));
+	if (IS_ERR(pdev2)) {
+		ret = PTR_ERR(pdev2);
+		goto err_unregister_tty;
+	}
+
+	pdev3 = platform_device_register_simple("qemu-virt-ctrl",
+						PLATFORM_DEVID_NONE,
+						virt_ctrl_res,
+						ARRAY_SIZE(virt_ctrl_res));
+	if (IS_ERR(pdev3)) {
+		ret = PTR_ERR(pdev3);
+		goto err_unregister_rtc;
+	}
+
+	for (i = 0; i < VIRTIO_BUS_NB; i++) {
+		pdevs[i] = virt_virtio_init(i);
+		if (IS_ERR(pdevs[i])) {
+			ret = PTR_ERR(pdevs[i]);
+			goto err_unregister_virtio;
+		}
+	}
+
+	return 0;
+
+err_unregister_virtio:
+	while (i > 0)
+		platform_device_unregister(pdevs[--i]);
+	platform_device_unregister(pdev3);
+err_unregister_rtc:
+	platform_device_unregister(pdev2);
+err_unregister_tty:
+	platform_device_unregister(pdev1);
+
+	return ret;
+}
+
+arch_initcall(virt_platform_init);