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, 133 insertions, 0 deletions

diff --git a/drivers/parisc/asp.c b/drivers/parisc/asp.c
new file mode 100644
index 000000000..32af8f095
--- /dev/null
+++ b/drivers/parisc/asp.c
@@ -0,0 +1,133 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *	ASP Device Driver
+ *
+ *	(c) Copyright 2000 The Puffin Group Inc.
+ *
+ *	(c) 2000-2023 by Helge Deller <deller@gmx.de>
+ */
+
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <asm/io.h>
+#include <asm/led.h>
+
+#include "gsc.h"
+
+#define ASP_GSC_IRQ	3		/* hardcoded interrupt for GSC */
+
+#define ASP_VER_OFFSET 	0x20		/* offset of ASP version */
+
+#define ASP_LED_ADDR	0xf0800020
+
+#define VIPER_INT_WORD  0xFFFBF088      /* addr of viper interrupt word */
+
+static struct gsc_asic asp;
+
+static void asp_choose_irq(struct parisc_device *dev, void *ctrl)
+{
+	int irq;
+
+	switch (dev->id.sversion) {
+	case 0x71:	irq =  9; break; /* SCSI */
+	case 0x72:	irq =  8; break; /* LAN */
+	case 0x73:	irq =  1; break; /* HIL */
+	case 0x74:	irq =  7; break; /* Centronics */
+	case 0x75:	irq = (dev->hw_path == 4) ? 5 : 6; break; /* RS232 */
+	case 0x76:	irq = 10; break; /* EISA BA */
+	case 0x77:	irq = 11; break; /* Graphics1 */
+	case 0x7a:	irq = 13; break; /* Audio (Bushmaster) */
+	case 0x7b:	irq = 13; break; /* Audio (Scorpio) */
+	case 0x7c:	irq =  3; break; /* FW SCSI */
+	case 0x7d:	irq =  4; break; /* FDDI */
+	case 0x7f:	irq = 13; break; /* Audio (Outfield) */
+	default:	return;		 /* Unknown */
+	}
+
+	gsc_asic_assign_irq(ctrl, irq, &dev->irq);
+
+	switch (dev->id.sversion) {
+	case 0x73:	irq =  2; break; /* i8042 High-priority */
+	case 0x76:	irq =  0; break; /* EISA BA */
+	default:	return;		 /* Other */
+	}
+
+	gsc_asic_assign_irq(ctrl, irq, &dev->aux_irq);
+}
+
+/* There are two register ranges we're interested in.  Interrupt /
+ * Status / LED are at 0xf080xxxx and Asp special registers are at
+ * 0xf082fxxx.  PDC only tells us that Asp is at 0xf082f000, so for
+ * the purposes of interrupt handling, we have to tell other bits of
+ * the kernel to look at the other registers.
+ */
+#define ASP_INTERRUPT_ADDR 0xf0800000
+
+static int __init asp_init_chip(struct parisc_device *dev)
+{
+	struct gsc_irq gsc_irq;
+	int ret;
+
+	asp.version = gsc_readb(dev->hpa.start + ASP_VER_OFFSET) & 0xf;
+	asp.name = (asp.version == 1) ? "Asp" : "Cutoff";
+	asp.hpa = ASP_INTERRUPT_ADDR;
+
+	printk(KERN_INFO "%s version %d at 0x%lx found.\n", 
+		asp.name, asp.version, (unsigned long)dev->hpa.start);
+
+	/* the IRQ ASP should use */
+	ret = -EBUSY;
+	dev->irq = gsc_claim_irq(&gsc_irq, ASP_GSC_IRQ);
+	if (dev->irq < 0) {
+		printk(KERN_ERR "%s(): cannot get GSC irq\n", __func__);
+		goto out;
+	}
+
+	asp.eim = ((u32) gsc_irq.txn_addr) | gsc_irq.txn_data;
+
+	ret = request_irq(gsc_irq.irq, gsc_asic_intr, 0, "asp", &asp);
+	if (ret < 0)
+		goto out;
+
+	/* Program VIPER to interrupt on the ASP irq */
+	gsc_writel((1 << (31 - ASP_GSC_IRQ)),VIPER_INT_WORD);
+
+	/* Done init'ing, register this driver */
+	ret = gsc_common_setup(dev, &asp);
+	if (ret)
+		goto out;
+
+	gsc_fixup_irqs(dev, &asp, asp_choose_irq);
+	/* Mongoose is a sibling of Asp, not a child... */
+	gsc_fixup_irqs(parisc_parent(dev), &asp, asp_choose_irq);
+
+	/* initialize the chassis LEDs */ 
+#ifdef CONFIG_CHASSIS_LCD_LED	
+	register_led_driver(DISPLAY_MODEL_OLD_ASP, LED_CMD_REG_NONE, 
+		    ASP_LED_ADDR);
+#endif
+
+ out:
+	return ret;
+}
+
+static const struct parisc_device_id asp_tbl[] __initconst = {
+	{ HPHW_BA, HVERSION_REV_ANY_ID, HVERSION_ANY_ID, 0x00070 },
+	{ 0, }
+};
+MODULE_DEVICE_TABLE(parisc, asp_tbl);
+
+static struct parisc_driver asp_driver __refdata = {
+	.name =		"asp",
+	.id_table =	asp_tbl,
+	.probe =	asp_init_chip,
+};
+
+static int __init asp_init(void)
+{
+	return register_parisc_driver(&asp_driver);
+}
+arch_initcall(asp_init);