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, 262 insertions, 0 deletions

diff --git a/drivers/parisc/gsc.c b/drivers/parisc/gsc.c
new file mode 100644
index 000000000..8ba778170
--- /dev/null
+++ b/drivers/parisc/gsc.c
@@ -0,0 +1,262 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Interrupt management for most GSC and related devices.
+ *
+ * (c) Copyright 1999 Alex deVries for The Puffin Group
+ * (c) Copyright 1999 Grant Grundler for Hewlett-Packard
+ * (c) Copyright 1999 Matthew Wilcox
+ * (c) Copyright 2000 Helge Deller
+ * (c) Copyright 2001 Matthew Wilcox for Hewlett-Packard
+ */
+
+#include <linux/bitops.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/ioport.h>
+#include <linux/module.h>
+#include <linux/types.h>
+
+#include <asm/hardware.h>
+#include <asm/io.h>
+
+#include "gsc.h"
+
+#undef DEBUG
+
+#ifdef DEBUG
+#define DEBPRINTK printk
+#else
+#define DEBPRINTK(x,...)
+#endif
+
+int gsc_alloc_irq(struct gsc_irq *i)
+{
+	int irq = txn_alloc_irq(GSC_EIM_WIDTH);
+	if (irq < 0) {
+		printk("cannot get irq\n");
+		return irq;
+	}
+
+	i->txn_addr = txn_alloc_addr(irq);
+	i->txn_data = txn_alloc_data(irq);
+	i->irq = irq;
+
+	return irq;
+}
+
+int gsc_claim_irq(struct gsc_irq *i, int irq)
+{
+	int c = irq;
+
+	irq += CPU_IRQ_BASE; /* virtualize the IRQ first */
+
+	irq = txn_claim_irq(irq);
+	if (irq < 0) {
+		printk("cannot claim irq %d\n", c);
+		return irq;
+	}
+
+	i->txn_addr = txn_alloc_addr(irq);
+	i->txn_data = txn_alloc_data(irq);
+	i->irq = irq;
+
+	return irq;
+}
+
+EXPORT_SYMBOL(gsc_alloc_irq);
+EXPORT_SYMBOL(gsc_claim_irq);
+
+/* Common interrupt demultiplexer used by Asp, Lasi & Wax.  */
+irqreturn_t gsc_asic_intr(int gsc_asic_irq, void *dev)
+{
+	unsigned long irr;
+	struct gsc_asic *gsc_asic = dev;
+
+	irr = gsc_readl(gsc_asic->hpa + OFFSET_IRR);
+	if (irr == 0)
+		return IRQ_NONE;
+
+	DEBPRINTK("%s intr, mask=0x%x\n", gsc_asic->name, irr);
+
+	do {
+		int local_irq = __ffs(irr);
+		unsigned int irq = gsc_asic->global_irq[local_irq];
+		generic_handle_irq(irq);
+		irr &= ~(1 << local_irq);
+	} while (irr);
+
+	return IRQ_HANDLED;
+}
+
+int gsc_find_local_irq(unsigned int irq, int *global_irqs, int limit)
+{
+	int local_irq;
+
+	for (local_irq = 0; local_irq < limit; local_irq++) {
+		if (global_irqs[local_irq] == irq)
+			return local_irq;
+	}
+
+	return NO_IRQ;
+}
+
+static void gsc_asic_mask_irq(struct irq_data *d)
+{
+	struct gsc_asic *irq_dev = irq_data_get_irq_chip_data(d);
+	int local_irq = gsc_find_local_irq(d->irq, irq_dev->global_irq, 32);
+	u32 imr;
+
+	DEBPRINTK(KERN_DEBUG "%s(%d) %s: IMR 0x%x\n", __func__, d->irq,
+			irq_dev->name, imr);
+
+	/* Disable the IRQ line by clearing the bit in the IMR */
+	imr = gsc_readl(irq_dev->hpa + OFFSET_IMR);
+	imr &= ~(1 << local_irq);
+	gsc_writel(imr, irq_dev->hpa + OFFSET_IMR);
+}
+
+static void gsc_asic_unmask_irq(struct irq_data *d)
+{
+	struct gsc_asic *irq_dev = irq_data_get_irq_chip_data(d);
+	int local_irq = gsc_find_local_irq(d->irq, irq_dev->global_irq, 32);
+	u32 imr;
+
+	DEBPRINTK(KERN_DEBUG "%s(%d) %s: IMR 0x%x\n", __func__, d->irq,
+			irq_dev->name, imr);
+
+	/* Enable the IRQ line by setting the bit in the IMR */
+	imr = gsc_readl(irq_dev->hpa + OFFSET_IMR);
+	imr |= 1 << local_irq;
+	gsc_writel(imr, irq_dev->hpa + OFFSET_IMR);
+	/*
+	 * FIXME: read IPR to make sure the IRQ isn't already pending.
+	 *   If so, we need to read IRR and manually call do_irq().
+	 */
+}
+
+#ifdef CONFIG_SMP
+static int gsc_set_affinity_irq(struct irq_data *d, const struct cpumask *dest,
+				bool force)
+{
+	struct gsc_asic *gsc_dev = irq_data_get_irq_chip_data(d);
+	struct cpumask tmask;
+	int cpu_irq;
+
+	if (!cpumask_and(&tmask, dest, cpu_online_mask))
+		return -EINVAL;
+
+	cpu_irq = cpu_check_affinity(d, &tmask);
+	if (cpu_irq < 0)
+		return cpu_irq;
+
+	gsc_dev->gsc_irq.txn_addr = txn_affinity_addr(d->irq, cpu_irq);
+	gsc_dev->eim = ((u32) gsc_dev->gsc_irq.txn_addr) | gsc_dev->gsc_irq.txn_data;
+
+	/* switch IRQ's for devices below LASI/WAX to other CPU */
+	/* ASP chip (svers 0x70) does not support reprogramming */
+	if (gsc_dev->gsc->id.sversion != 0x70)
+		gsc_writel(gsc_dev->eim, gsc_dev->hpa + OFFSET_IAR);
+
+	irq_data_update_effective_affinity(d, &tmask);
+
+	return IRQ_SET_MASK_OK;
+}
+#endif
+
+
+static struct irq_chip gsc_asic_interrupt_type = {
+	.name		=	"GSC-ASIC",
+	.irq_unmask	=	gsc_asic_unmask_irq,
+	.irq_mask	=	gsc_asic_mask_irq,
+#ifdef CONFIG_SMP
+	.irq_set_affinity =	gsc_set_affinity_irq,
+#endif
+};
+
+int gsc_assign_irq(struct irq_chip *type, void *data)
+{
+	static int irq = GSC_IRQ_BASE;
+
+	if (irq > GSC_IRQ_MAX)
+		return NO_IRQ;
+
+	irq_set_chip_and_handler(irq, type, handle_simple_irq);
+	irq_set_chip_data(irq, data);
+
+	return irq++;
+}
+
+void gsc_asic_assign_irq(struct gsc_asic *asic, int local_irq, int *irqp)
+{
+	int irq = asic->global_irq[local_irq];
+	
+	if (irq <= 0) {
+		irq = gsc_assign_irq(&gsc_asic_interrupt_type, asic);
+		if (irq == NO_IRQ)
+			return;
+
+		asic->global_irq[local_irq] = irq;
+	}
+	*irqp = irq;
+}
+
+struct gsc_fixup_struct {
+	void (*choose_irq)(struct parisc_device *, void *);
+	void *ctrl;
+};
+
+static int gsc_fixup_irqs_callback(struct device *dev, void *data)
+{
+	struct parisc_device *padev = to_parisc_device(dev);
+	struct gsc_fixup_struct *gf = data;
+
+	/* work-around for 715/64 and others which have parent
+	   at path [5] and children at path [5/0/x] */
+	if (padev->id.hw_type == HPHW_FAULTY)
+		gsc_fixup_irqs(padev, gf->ctrl, gf->choose_irq);
+	gf->choose_irq(padev, gf->ctrl);
+
+	return 0;
+}
+
+void gsc_fixup_irqs(struct parisc_device *parent, void *ctrl,
+			void (*choose_irq)(struct parisc_device *, void *))
+{
+	struct gsc_fixup_struct data = {
+		.choose_irq	= choose_irq,
+		.ctrl		= ctrl,
+	};
+
+	device_for_each_child(&parent->dev, &data, gsc_fixup_irqs_callback);
+}
+
+int gsc_common_setup(struct parisc_device *parent, struct gsc_asic *gsc_asic)
+{
+	struct resource *res;
+	int i;
+
+	gsc_asic->gsc = parent;
+
+	/* Initialise local irq -> global irq mapping */
+	for (i = 0; i < 32; i++) {
+		gsc_asic->global_irq[i] = NO_IRQ;
+	}
+
+	/* allocate resource region */
+	res = request_mem_region(gsc_asic->hpa, 0x100000, gsc_asic->name);
+	if (res) {
+		res->flags = IORESOURCE_MEM; 	/* do not mark it busy ! */
+	}
+
+#if 0
+	printk(KERN_WARNING "%s IRQ %d EIM 0x%x", gsc_asic->name,
+			parent->irq, gsc_asic->eim);
+	if (gsc_readl(gsc_asic->hpa + OFFSET_IMR))
+		printk("  IMR is non-zero! (0x%x)",
+				gsc_readl(gsc_asic->hpa + OFFSET_IMR));
+	printk("\n");
+#endif
+
+	return 0;
+}