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, 283 insertions, 0 deletions

diff --git a/arch/powerpc/sysdev/i8259.c b/arch/powerpc/sysdev/i8259.c
new file mode 100644
index 000000000..99bb2b916
--- /dev/null
+++ b/arch/powerpc/sysdev/i8259.c
@@ -0,0 +1,283 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * i8259 interrupt controller driver.
+ */
+#undef DEBUG
+
+#include <linux/ioport.h>
+#include <linux/interrupt.h>
+#include <linux/irqdomain.h>
+#include <linux/kernel.h>
+#include <linux/delay.h>
+#include <asm/io.h>
+#include <asm/i8259.h>
+
+static volatile void __iomem *pci_intack; /* RO, gives us the irq vector */
+
+static unsigned char cached_8259[2] = { 0xff, 0xff };
+#define cached_A1 (cached_8259[0])
+#define cached_21 (cached_8259[1])
+
+static DEFINE_RAW_SPINLOCK(i8259_lock);
+
+static struct irq_domain *i8259_host;
+
+/*
+ * Acknowledge the IRQ using either the PCI host bridge's interrupt
+ * acknowledge feature or poll.  How i8259_init() is called determines
+ * which is called.  It should be noted that polling is broken on some
+ * IBM and Motorola PReP boxes so we must use the int-ack feature on them.
+ */
+unsigned int i8259_irq(void)
+{
+	int irq;
+	int lock = 0;
+
+	/* Either int-ack or poll for the IRQ */
+	if (pci_intack)
+		irq = readb(pci_intack);
+	else {
+		raw_spin_lock(&i8259_lock);
+		lock = 1;
+
+		/* Perform an interrupt acknowledge cycle on controller 1. */
+		outb(0x0C, 0x20);		/* prepare for poll */
+		irq = inb(0x20) & 7;
+		if (irq == 2 ) {
+			/*
+			 * Interrupt is cascaded so perform interrupt
+			 * acknowledge on controller 2.
+			 */
+			outb(0x0C, 0xA0);	/* prepare for poll */
+			irq = (inb(0xA0) & 7) + 8;
+		}
+	}
+
+	if (irq == 7) {
+		/*
+		 * This may be a spurious interrupt.
+		 *
+		 * Read the interrupt status register (ISR). If the most
+		 * significant bit is not set then there is no valid
+		 * interrupt.
+		 */
+		if (!pci_intack)
+			outb(0x0B, 0x20);	/* ISR register */
+		if(~inb(0x20) & 0x80)
+			irq = 0;
+	} else if (irq == 0xff)
+		irq = 0;
+
+	if (lock)
+		raw_spin_unlock(&i8259_lock);
+	return irq;
+}
+
+static void i8259_mask_and_ack_irq(struct irq_data *d)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&i8259_lock, flags);
+	if (d->irq > 7) {
+		cached_A1 |= 1 << (d->irq-8);
+		inb(0xA1); 	/* DUMMY */
+		outb(cached_A1, 0xA1);
+		outb(0x20, 0xA0);	/* Non-specific EOI */
+		outb(0x20, 0x20);	/* Non-specific EOI to cascade */
+	} else {
+		cached_21 |= 1 << d->irq;
+		inb(0x21); 	/* DUMMY */
+		outb(cached_21, 0x21);
+		outb(0x20, 0x20);	/* Non-specific EOI */
+	}
+	raw_spin_unlock_irqrestore(&i8259_lock, flags);
+}
+
+static void i8259_set_irq_mask(int irq_nr)
+{
+	outb(cached_A1,0xA1);
+	outb(cached_21,0x21);
+}
+
+static void i8259_mask_irq(struct irq_data *d)
+{
+	unsigned long flags;
+
+	pr_debug("i8259_mask_irq(%d)\n", d->irq);
+
+	raw_spin_lock_irqsave(&i8259_lock, flags);
+	if (d->irq < 8)
+		cached_21 |= 1 << d->irq;
+	else
+		cached_A1 |= 1 << (d->irq-8);
+	i8259_set_irq_mask(d->irq);
+	raw_spin_unlock_irqrestore(&i8259_lock, flags);
+}
+
+static void i8259_unmask_irq(struct irq_data *d)
+{
+	unsigned long flags;
+
+	pr_debug("i8259_unmask_irq(%d)\n", d->irq);
+
+	raw_spin_lock_irqsave(&i8259_lock, flags);
+	if (d->irq < 8)
+		cached_21 &= ~(1 << d->irq);
+	else
+		cached_A1 &= ~(1 << (d->irq-8));
+	i8259_set_irq_mask(d->irq);
+	raw_spin_unlock_irqrestore(&i8259_lock, flags);
+}
+
+static struct irq_chip i8259_pic = {
+	.name		= "i8259",
+	.irq_mask	= i8259_mask_irq,
+	.irq_disable	= i8259_mask_irq,
+	.irq_unmask	= i8259_unmask_irq,
+	.irq_mask_ack	= i8259_mask_and_ack_irq,
+};
+
+static struct resource pic1_iores = {
+	.name = "8259 (master)",
+	.start = 0x20,
+	.end = 0x21,
+	.flags = IORESOURCE_IO | IORESOURCE_BUSY,
+};
+
+static struct resource pic2_iores = {
+	.name = "8259 (slave)",
+	.start = 0xa0,
+	.end = 0xa1,
+	.flags = IORESOURCE_IO | IORESOURCE_BUSY,
+};
+
+static struct resource pic_edgectrl_iores = {
+	.name = "8259 edge control",
+	.start = 0x4d0,
+	.end = 0x4d1,
+	.flags = IORESOURCE_IO | IORESOURCE_BUSY,
+};
+
+static int i8259_host_match(struct irq_domain *h, struct device_node *node,
+			    enum irq_domain_bus_token bus_token)
+{
+	struct device_node *of_node = irq_domain_get_of_node(h);
+	return of_node == NULL || of_node == node;
+}
+
+static int i8259_host_map(struct irq_domain *h, unsigned int virq,
+			  irq_hw_number_t hw)
+{
+	pr_debug("i8259_host_map(%d, 0x%lx)\n", virq, hw);
+
+	/* We block the internal cascade */
+	if (hw == 2)
+		irq_set_status_flags(virq, IRQ_NOREQUEST);
+
+	/* We use the level handler only for now, we might want to
+	 * be more cautious here but that works for now
+	 */
+	irq_set_status_flags(virq, IRQ_LEVEL);
+	irq_set_chip_and_handler(virq, &i8259_pic, handle_level_irq);
+	return 0;
+}
+
+static int i8259_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)
+{
+	static unsigned char map_isa_senses[4] = {
+		IRQ_TYPE_LEVEL_LOW,
+		IRQ_TYPE_LEVEL_HIGH,
+		IRQ_TYPE_EDGE_FALLING,
+		IRQ_TYPE_EDGE_RISING,
+	};
+
+	*out_hwirq = intspec[0];
+	if (intsize > 1 && intspec[1] < 4)
+		*out_flags = map_isa_senses[intspec[1]];
+	else
+		*out_flags = IRQ_TYPE_NONE;
+
+	return 0;
+}
+
+static const struct irq_domain_ops i8259_host_ops = {
+	.match = i8259_host_match,
+	.map = i8259_host_map,
+	.xlate = i8259_host_xlate,
+};
+
+struct irq_domain *__init i8259_get_host(void)
+{
+	return i8259_host;
+}
+
+/**
+ * i8259_init - Initialize the legacy controller
+ * @node: device node of the legacy PIC (can be NULL, but then, it will match
+ *        all interrupts, so beware)
+ * @intack_addr: PCI interrupt acknowledge (real) address which will return
+ *             	 the active irq from the 8259
+ */
+void i8259_init(struct device_node *node, unsigned long intack_addr)
+{
+	unsigned long flags;
+
+	/* initialize the controller */
+	raw_spin_lock_irqsave(&i8259_lock, flags);
+
+	/* Mask all first */
+	outb(0xff, 0xA1);
+	outb(0xff, 0x21);
+
+	/* init master interrupt controller */
+	outb(0x11, 0x20); /* Start init sequence */
+	outb(0x00, 0x21); /* Vector base */
+	outb(0x04, 0x21); /* edge triggered, Cascade (slave) on IRQ2 */
+	outb(0x01, 0x21); /* Select 8086 mode */
+
+	/* init slave interrupt controller */
+	outb(0x11, 0xA0); /* Start init sequence */
+	outb(0x08, 0xA1); /* Vector base */
+	outb(0x02, 0xA1); /* edge triggered, Cascade (slave) on IRQ2 */
+	outb(0x01, 0xA1); /* Select 8086 mode */
+
+	/* That thing is slow */
+	udelay(100);
+
+	/* always read ISR */
+	outb(0x0B, 0x20);
+	outb(0x0B, 0xA0);
+
+	/* Unmask the internal cascade */
+	cached_21 &= ~(1 << 2);
+
+	/* Set interrupt masks */
+	outb(cached_A1, 0xA1);
+	outb(cached_21, 0x21);
+
+	raw_spin_unlock_irqrestore(&i8259_lock, flags);
+
+	/* create a legacy host */
+	i8259_host = irq_domain_create_legacy(of_fwnode_handle(node), NR_IRQS_LEGACY, 0, 0,
+					      &i8259_host_ops, NULL);
+	if (i8259_host == NULL) {
+		printk(KERN_ERR "i8259: failed to allocate irq host !\n");
+		return;
+	}
+
+	/* reserve our resources */
+	/* XXX should we continue doing that ? it seems to cause problems
+	 * with further requesting of PCI IO resources for that range...
+	 * need to look into it.
+	 */
+	request_resource(&ioport_resource, &pic1_iores);
+	request_resource(&ioport_resource, &pic2_iores);
+	request_resource(&ioport_resource, &pic_edgectrl_iores);
+
+	if (intack_addr != 0)
+		pci_intack = ioremap(intack_addr, 1);
+
+	printk(KERN_INFO "i8259 legacy interrupt controller initialized\n");
+}