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>

3 files changed, 265 insertions, 0 deletions

diff --git a/arch/powerpc/sysdev/ge/Makefile b/arch/powerpc/sysdev/ge/Makefile
new file mode 100644
index 000000000..a63fdb379
--- /dev/null
+++ b/arch/powerpc/sysdev/ge/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_GE_FPGA)		+= ge_pic.o
diff --git a/arch/powerpc/sysdev/ge/ge_pic.c b/arch/powerpc/sysdev/ge/ge_pic.c
new file mode 100644
index 000000000..0bc3f0b36
--- /dev/null
+++ b/arch/powerpc/sysdev/ge/ge_pic.c
@@ -0,0 +1,254 @@
+/*
+ * Interrupt handling for GE FPGA based PIC
+ *
+ * Author: Martyn Welch <martyn.welch@ge.com>
+ *
+ * 2008 (c) GE Intelligent Platforms Embedded Systems, Inc.
+ *
+ * This file is licensed under the terms of the GNU General Public License
+ * version 2.  This program is licensed "as is" without any warranty of any
+ * kind, whether express or implied.
+ */
+
+#include <linux/stddef.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/irq.h>
+#include <linux/irqdomain.h>
+#include <linux/interrupt.h>
+#include <linux/of_address.h>
+#include <linux/of_irq.h>
+#include <linux/spinlock.h>
+
+#include <asm/byteorder.h>
+#include <asm/io.h>
+#include <asm/irq.h>
+
+#include "ge_pic.h"
+
+#define DEBUG
+#undef DEBUG
+
+#ifdef DEBUG
+#define DBG(fmt...) do { printk(KERN_DEBUG "gef_pic: " fmt); } while (0)
+#else
+#define DBG(fmt...) do { } while (0)
+#endif
+
+#define GEF_PIC_NUM_IRQS	32
+
+/* Interrupt Controller Interface Registers */
+#define GEF_PIC_INTR_STATUS	0x0000
+
+#define GEF_PIC_INTR_MASK(cpu)	(0x0010 + (0x4 * cpu))
+#define GEF_PIC_CPU0_INTR_MASK	GEF_PIC_INTR_MASK(0)
+#define GEF_PIC_CPU1_INTR_MASK	GEF_PIC_INTR_MASK(1)
+
+#define GEF_PIC_MCP_MASK(cpu)	(0x0018 + (0x4 * cpu))
+#define GEF_PIC_CPU0_MCP_MASK	GEF_PIC_MCP_MASK(0)
+#define GEF_PIC_CPU1_MCP_MASK	GEF_PIC_MCP_MASK(1)
+
+
+static DEFINE_RAW_SPINLOCK(gef_pic_lock);
+
+static void __iomem *gef_pic_irq_reg_base;
+static struct irq_domain *gef_pic_irq_host;
+static int gef_pic_cascade_irq;
+
+/*
+ * Interrupt Controller Handling
+ *
+ * The interrupt controller handles interrupts for most on board interrupts,
+ * apart from PCI interrupts. For example on SBC610:
+ *
+ * 17:31 RO Reserved
+ * 16    RO PCI Express Doorbell 3 Status
+ * 15    RO PCI Express Doorbell 2 Status
+ * 14    RO PCI Express Doorbell 1 Status
+ * 13    RO PCI Express Doorbell 0 Status
+ * 12    RO Real Time Clock Interrupt Status
+ * 11    RO Temperature Interrupt Status
+ * 10    RO Temperature Critical Interrupt Status
+ * 9     RO Ethernet PHY1 Interrupt Status
+ * 8     RO Ethernet PHY3 Interrupt Status
+ * 7     RO PEX8548 Interrupt Status
+ * 6     RO Reserved
+ * 5     RO Watchdog 0 Interrupt Status
+ * 4     RO Watchdog 1 Interrupt Status
+ * 3     RO AXIS Message FIFO A Interrupt Status
+ * 2     RO AXIS Message FIFO B Interrupt Status
+ * 1     RO AXIS Message FIFO C Interrupt Status
+ * 0     RO AXIS Message FIFO D Interrupt Status
+ *
+ * Interrupts can be forwarded to one of two output lines. Nothing
+ * clever is done, so if the masks are incorrectly set, a single input
+ * interrupt could generate interrupts on both output lines!
+ *
+ * The dual lines are there to allow the chained interrupts to be easily
+ * passed into two different cores. We currently do not use this functionality
+ * in this driver.
+ *
+ * Controller can also be configured to generate Machine checks (MCP), again on
+ * two lines, to be attached to two different cores. It is suggested that these
+ * should be masked out.
+ */
+
+static void gef_pic_cascade(struct irq_desc *desc)
+{
+	struct irq_chip *chip = irq_desc_get_chip(desc);
+	unsigned int cascade_irq;
+
+	/*
+	 * See if we actually have an interrupt, call generic handling code if
+	 * we do.
+	 */
+	cascade_irq = gef_pic_get_irq();
+
+	if (cascade_irq)
+		generic_handle_irq(cascade_irq);
+
+	chip->irq_eoi(&desc->irq_data);
+}
+
+static void gef_pic_mask(struct irq_data *d)
+{
+	unsigned long flags;
+	unsigned int hwirq = irqd_to_hwirq(d);
+	u32 mask;
+
+	raw_spin_lock_irqsave(&gef_pic_lock, flags);
+	mask = in_be32(gef_pic_irq_reg_base + GEF_PIC_INTR_MASK(0));
+	mask &= ~(1 << hwirq);
+	out_be32(gef_pic_irq_reg_base + GEF_PIC_INTR_MASK(0), mask);
+	raw_spin_unlock_irqrestore(&gef_pic_lock, flags);
+}
+
+static void gef_pic_mask_ack(struct irq_data *d)
+{
+	/* Don't think we actually have to do anything to ack an interrupt,
+	 * we just need to clear down the devices interrupt and it will go away
+	 */
+	gef_pic_mask(d);
+}
+
+static void gef_pic_unmask(struct irq_data *d)
+{
+	unsigned long flags;
+	unsigned int hwirq = irqd_to_hwirq(d);
+	u32 mask;
+
+	raw_spin_lock_irqsave(&gef_pic_lock, flags);
+	mask = in_be32(gef_pic_irq_reg_base + GEF_PIC_INTR_MASK(0));
+	mask |= (1 << hwirq);
+	out_be32(gef_pic_irq_reg_base + GEF_PIC_INTR_MASK(0), mask);
+	raw_spin_unlock_irqrestore(&gef_pic_lock, flags);
+}
+
+static struct irq_chip gef_pic_chip = {
+	.name		= "gefp",
+	.irq_mask	= gef_pic_mask,
+	.irq_mask_ack	= gef_pic_mask_ack,
+	.irq_unmask	= gef_pic_unmask,
+};
+
+
+/* When an interrupt is being configured, this call allows some flexibility
+ * in deciding which irq_chip structure is used
+ */
+static int gef_pic_host_map(struct irq_domain *h, unsigned int virq,
+			  irq_hw_number_t hwirq)
+{
+	/* All interrupts are LEVEL sensitive */
+	irq_set_status_flags(virq, IRQ_LEVEL);
+	irq_set_chip_and_handler(virq, &gef_pic_chip, handle_level_irq);
+
+	return 0;
+}
+
+static int gef_pic_host_xlate(struct irq_domain *h, struct device_node *ct,
+			    const u32 *intspec, unsigned int intsize,
+			    irq_hw_number_t *out_hwirq, unsigned int *out_flags)
+{
+
+	*out_hwirq = intspec[0];
+	if (intsize > 1)
+		*out_flags = intspec[1];
+	else
+		*out_flags = IRQ_TYPE_LEVEL_HIGH;
+
+	return 0;
+}
+
+static const struct irq_domain_ops gef_pic_host_ops = {
+	.map	= gef_pic_host_map,
+	.xlate	= gef_pic_host_xlate,
+};
+
+
+/*
+ * Initialisation of PIC, this should be called in BSP
+ */
+void __init gef_pic_init(struct device_node *np)
+{
+	unsigned long flags;
+
+	/* Map the devices registers into memory */
+	gef_pic_irq_reg_base = of_iomap(np, 0);
+
+	raw_spin_lock_irqsave(&gef_pic_lock, flags);
+
+	/* Initialise everything as masked. */
+	out_be32(gef_pic_irq_reg_base + GEF_PIC_CPU0_INTR_MASK, 0);
+	out_be32(gef_pic_irq_reg_base + GEF_PIC_CPU1_INTR_MASK, 0);
+
+	out_be32(gef_pic_irq_reg_base + GEF_PIC_CPU0_MCP_MASK, 0);
+	out_be32(gef_pic_irq_reg_base + GEF_PIC_CPU1_MCP_MASK, 0);
+
+	raw_spin_unlock_irqrestore(&gef_pic_lock, flags);
+
+	/* Map controller */
+	gef_pic_cascade_irq = irq_of_parse_and_map(np, 0);
+	if (!gef_pic_cascade_irq) {
+		printk(KERN_ERR "SBC610: failed to map cascade interrupt");
+		return;
+	}
+
+	/* Setup an irq_domain structure */
+	gef_pic_irq_host = irq_domain_create_linear(of_fwnode_handle(np),
+						    GEF_PIC_NUM_IRQS,
+						    &gef_pic_host_ops, NULL);
+	if (gef_pic_irq_host == NULL)
+		return;
+
+	/* Chain with parent controller */
+	irq_set_chained_handler(gef_pic_cascade_irq, gef_pic_cascade);
+}
+
+/*
+ * This is called when we receive an interrupt with apparently comes from this
+ * chip - check, returning the highest interrupt generated or return 0.
+ */
+unsigned int gef_pic_get_irq(void)
+{
+	u32 cause, mask, active;
+	unsigned int virq = 0;
+	int hwirq;
+
+	cause = in_be32(gef_pic_irq_reg_base + GEF_PIC_INTR_STATUS);
+
+	mask = in_be32(gef_pic_irq_reg_base + GEF_PIC_INTR_MASK(0));
+
+	active = cause & mask;
+
+	if (active) {
+		for (hwirq = GEF_PIC_NUM_IRQS - 1; hwirq > -1; hwirq--) {
+			if (active & (0x1 << hwirq))
+				break;
+		}
+		virq = irq_find_mapping(gef_pic_irq_host,
+			(irq_hw_number_t)hwirq);
+	}
+
+	return virq;
+}
+
diff --git a/arch/powerpc/sysdev/ge/ge_pic.h b/arch/powerpc/sysdev/ge/ge_pic.h
new file mode 100644
index 000000000..923dedba3
--- /dev/null
+++ b/arch/powerpc/sysdev/ge/ge_pic.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __GEF_PIC_H__
+#define __GEF_PIC_H__
+
+unsigned int gef_pic_get_irq(void);
+void gef_pic_init(struct device_node *);
+
+#endif /* __GEF_PIC_H__ */
+