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, 46 insertions, 0 deletions

diff --git a/include/net/ax88796.h b/include/net/ax88796.h
new file mode 100644
index 000000000..303100f08
--- /dev/null
+++ b/include/net/ax88796.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* include/net/ax88796.h
+ *
+ * Copyright 2005 Simtec Electronics
+ *	Ben Dooks <ben@simtec.co.uk>
+*/
+
+#ifndef __NET_AX88796_PLAT_H
+#define __NET_AX88796_PLAT_H
+
+#include <linux/types.h>
+
+struct sk_buff;
+struct net_device;
+struct platform_device;
+
+#define AXFLG_HAS_EEPROM		(1<<0)
+#define AXFLG_MAC_FROMDEV		(1<<1)	/* device already has MAC */
+#define AXFLG_HAS_93CX6			(1<<2)	/* use eeprom_93cx6 driver */
+#define AXFLG_MAC_FROMPLATFORM		(1<<3)	/* MAC given by platform data */
+
+struct ax_plat_data {
+	unsigned int	 flags;
+	unsigned char	 wordlength;	/* 1 or 2 */
+	unsigned char	 dcr_val;	/* default value for DCR */
+	unsigned char	 rcr_val;	/* default value for RCR */
+	unsigned char	 gpoc_val;	/* default value for GPOC */
+	u32		*reg_offsets;	/* register offsets */
+	u8		*mac_addr;	/* MAC addr (only used when
+					   AXFLG_MAC_FROMPLATFORM is used */
+
+	/* uses default ax88796 buffer if set to NULL */
+	void (*block_output)(struct net_device *dev, int count,
+			const unsigned char *buf, int star_page);
+	void (*block_input)(struct net_device *dev, int count,
+			struct sk_buff *skb, int ring_offset);
+	/* returns nonzero if a pending interrupt request might be caused by
+	 * the ax88796. Handles all interrupts if set to NULL
+	 */
+	int (*check_irq)(struct platform_device *pdev);
+};
+
+/* exported from ax88796.c for xsurf100.c  */
+extern void ax_NS8390_reinit(struct net_device *dev);
+
+#endif /* __NET_AX88796_PLAT_H */