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, 211 insertions, 0 deletions

diff --git a/drivers/sh/intc/chip.c b/drivers/sh/intc/chip.c
new file mode 100644
index 000000000..828d81e02
--- /dev/null
+++ b/drivers/sh/intc/chip.c
@@ -0,0 +1,211 @@
+/*
+ * IRQ chip definitions for INTC IRQs.
+ *
+ * Copyright (C) 2007, 2008 Magnus Damm
+ * Copyright (C) 2009 - 2012 Paul Mundt
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+#include <linux/cpumask.h>
+#include <linux/bsearch.h>
+#include <linux/io.h>
+#include "internals.h"
+
+void _intc_enable(struct irq_data *data, unsigned long handle)
+{
+	unsigned int irq = data->irq;
+	struct intc_desc_int *d = get_intc_desc(irq);
+	unsigned long addr;
+	unsigned int cpu;
+
+	for (cpu = 0; cpu < SMP_NR(d, _INTC_ADDR_E(handle)); cpu++) {
+#ifdef CONFIG_SMP
+		if (!cpumask_test_cpu(cpu, irq_data_get_affinity_mask(data)))
+			continue;
+#endif
+		addr = INTC_REG(d, _INTC_ADDR_E(handle), cpu);
+		intc_enable_fns[_INTC_MODE(handle)](addr, handle, intc_reg_fns\
+						    [_INTC_FN(handle)], irq);
+	}
+
+	intc_balancing_enable(irq);
+}
+
+static void intc_enable(struct irq_data *data)
+{
+	_intc_enable(data, (unsigned long)irq_data_get_irq_chip_data(data));
+}
+
+static void intc_disable(struct irq_data *data)
+{
+	unsigned int irq = data->irq;
+	struct intc_desc_int *d = get_intc_desc(irq);
+	unsigned long handle = (unsigned long)irq_data_get_irq_chip_data(data);
+	unsigned long addr;
+	unsigned int cpu;
+
+	intc_balancing_disable(irq);
+
+	for (cpu = 0; cpu < SMP_NR(d, _INTC_ADDR_D(handle)); cpu++) {
+#ifdef CONFIG_SMP
+		if (!cpumask_test_cpu(cpu, irq_data_get_affinity_mask(data)))
+			continue;
+#endif
+		addr = INTC_REG(d, _INTC_ADDR_D(handle), cpu);
+		intc_disable_fns[_INTC_MODE(handle)](addr, handle,intc_reg_fns\
+						     [_INTC_FN(handle)], irq);
+	}
+}
+
+#ifdef CONFIG_SMP
+/*
+ * This is held with the irq desc lock held, so we don't require any
+ * additional locking here at the intc desc level. The affinity mask is
+ * later tested in the enable/disable paths.
+ */
+static int intc_set_affinity(struct irq_data *data,
+			     const struct cpumask *cpumask,
+			     bool force)
+{
+	if (!cpumask_intersects(cpumask, cpu_online_mask))
+		return -1;
+
+	irq_data_update_affinity(data, cpumask);
+
+	return IRQ_SET_MASK_OK_NOCOPY;
+}
+#endif
+
+static void intc_mask_ack(struct irq_data *data)
+{
+	unsigned int irq = data->irq;
+	struct intc_desc_int *d = get_intc_desc(irq);
+	unsigned long handle = intc_get_ack_handle(irq);
+	void __iomem *addr;
+
+	intc_disable(data);
+
+	/* read register and write zero only to the associated bit */
+	if (handle) {
+		unsigned int value;
+
+		addr = (void __iomem *)INTC_REG(d, _INTC_ADDR_D(handle), 0);
+		value = intc_set_field_from_handle(0, 1, handle);
+
+		switch (_INTC_FN(handle)) {
+		case REG_FN_MODIFY_BASE + 0:	/* 8bit */
+			__raw_readb(addr);
+			__raw_writeb(0xff ^ value, addr);
+			break;
+		case REG_FN_MODIFY_BASE + 1:	/* 16bit */
+			__raw_readw(addr);
+			__raw_writew(0xffff ^ value, addr);
+			break;
+		case REG_FN_MODIFY_BASE + 3:	/* 32bit */
+			__raw_readl(addr);
+			__raw_writel(0xffffffff ^ value, addr);
+			break;
+		default:
+			BUG();
+			break;
+		}
+	}
+}
+
+static struct intc_handle_int *intc_find_irq(struct intc_handle_int *hp,
+					     unsigned int nr_hp,
+					     unsigned int irq)
+{
+	struct intc_handle_int key;
+
+	key.irq = irq;
+	key.handle = 0;
+
+	return bsearch(&key, hp, nr_hp, sizeof(*hp), intc_handle_int_cmp);
+}
+
+int intc_set_priority(unsigned int irq, unsigned int prio)
+{
+	struct intc_desc_int *d = get_intc_desc(irq);
+	struct irq_data *data = irq_get_irq_data(irq);
+	struct intc_handle_int *ihp;
+
+	if (!intc_get_prio_level(irq) || prio <= 1)
+		return -EINVAL;
+
+	ihp = intc_find_irq(d->prio, d->nr_prio, irq);
+	if (ihp) {
+		if (prio >= (1 << _INTC_WIDTH(ihp->handle)))
+			return -EINVAL;
+
+		intc_set_prio_level(irq, prio);
+
+		/*
+		 * only set secondary masking method directly
+		 * primary masking method is using intc_prio_level[irq]
+		 * priority level will be set during next enable()
+		 */
+		if (_INTC_FN(ihp->handle) != REG_FN_ERR)
+			_intc_enable(data, ihp->handle);
+	}
+	return 0;
+}
+
+#define SENSE_VALID_FLAG 0x80
+#define VALID(x) (x | SENSE_VALID_FLAG)
+
+static unsigned char intc_irq_sense_table[IRQ_TYPE_SENSE_MASK + 1] = {
+	[IRQ_TYPE_EDGE_FALLING] = VALID(0),
+	[IRQ_TYPE_EDGE_RISING] = VALID(1),
+	[IRQ_TYPE_LEVEL_LOW] = VALID(2),
+	/* SH7706, SH7707 and SH7709 do not support high level triggered */
+#if !defined(CONFIG_CPU_SUBTYPE_SH7706) && \
+    !defined(CONFIG_CPU_SUBTYPE_SH7707) && \
+    !defined(CONFIG_CPU_SUBTYPE_SH7709)
+	[IRQ_TYPE_LEVEL_HIGH] = VALID(3),
+#endif
+#if defined(CONFIG_ARM) /* all recent SH-Mobile / R-Mobile ARM support this */
+	[IRQ_TYPE_EDGE_BOTH] = VALID(4),
+#endif
+};
+
+static int intc_set_type(struct irq_data *data, unsigned int type)
+{
+	unsigned int irq = data->irq;
+	struct intc_desc_int *d = get_intc_desc(irq);
+	unsigned char value = intc_irq_sense_table[type & IRQ_TYPE_SENSE_MASK];
+	struct intc_handle_int *ihp;
+	unsigned long addr;
+
+	if (!value)
+		return -EINVAL;
+
+	value &= ~SENSE_VALID_FLAG;
+
+	ihp = intc_find_irq(d->sense, d->nr_sense, irq);
+	if (ihp) {
+		/* PINT has 2-bit sense registers, should fail on EDGE_BOTH */
+		if (value >= (1 << _INTC_WIDTH(ihp->handle)))
+			return -EINVAL;
+
+		addr = INTC_REG(d, _INTC_ADDR_E(ihp->handle), 0);
+		intc_reg_fns[_INTC_FN(ihp->handle)](addr, ihp->handle, value);
+	}
+
+	return 0;
+}
+
+struct irq_chip intc_irq_chip	= {
+	.irq_mask		= intc_disable,
+	.irq_unmask		= intc_enable,
+	.irq_mask_ack		= intc_mask_ack,
+	.irq_enable		= intc_enable,
+	.irq_disable		= intc_disable,
+	.irq_set_type		= intc_set_type,
+#ifdef CONFIG_SMP
+	.irq_set_affinity	= intc_set_affinity,
+#endif
+	.flags			= IRQCHIP_SKIP_SET_WAKE,
+};