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, 47 insertions, 0 deletions

diff --git a/drivers/parisc/gsc.h b/drivers/parisc/gsc.h
new file mode 100644
index 000000000..73cbd0bb1
--- /dev/null
+++ b/drivers/parisc/gsc.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * drivers/parisc/gsc.h
+ * Declarations for functions in gsc.c
+ * Copyright (c) 2000-2002 Helge Deller, Matthew Wilcox
+ */
+
+#include <linux/interrupt.h>
+#include <asm/hardware.h>
+#include <asm/parisc-device.h>
+
+#define OFFSET_IRR 0x0000   /* Interrupt request register */
+#define OFFSET_IMR 0x0004   /* Interrupt mask register */
+#define OFFSET_IPR 0x0008   /* Interrupt pending register */
+#define OFFSET_ICR 0x000C   /* Interrupt control register */
+#define OFFSET_IAR 0x0010   /* Interrupt address register */
+
+/* PA I/O Architected devices support at least 5 bits in the EIM register. */
+#define GSC_EIM_WIDTH 5
+
+struct gsc_irq {
+	unsigned long txn_addr;	/* IRQ "target" */
+	int txn_data;		/* HW "IRQ" */
+	int irq;		/* virtual IRQ */
+};
+
+struct gsc_asic {
+	struct parisc_device *gsc;
+	unsigned long hpa;
+	char *name;
+	int version;
+	int type;
+	int eim;
+	struct gsc_irq gsc_irq;
+	int global_irq[32];
+};
+
+int gsc_common_setup(struct parisc_device *parent, struct gsc_asic *gsc_asic);
+int gsc_alloc_irq(struct gsc_irq *dev);			/* dev needs an irq */
+int gsc_claim_irq(struct gsc_irq *dev, int irq);	/* dev needs this irq */
+int gsc_assign_irq(struct irq_chip *type, void *data);
+int gsc_find_local_irq(unsigned int irq, int *global_irq, int limit);
+void gsc_fixup_irqs(struct parisc_device *parent, void *ctrl,
+		void (*choose)(struct parisc_device *child, void *ctrl));
+void gsc_asic_assign_irq(struct gsc_asic *asic, int local_irq, int *irqp);
+
+irqreturn_t gsc_asic_intr(int irq, void *dev);