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, 44 insertions, 0 deletions

diff --git a/drivers/net/phy/sfp.h b/drivers/net/phy/sfp.h
new file mode 100644
index 000000000..879dff7af
--- /dev/null
+++ b/drivers/net/phy/sfp.h
@@ -0,0 +1,44 @@
+#ifndef SFP_H
+#define SFP_H
+
+#include <linux/ethtool.h>
+#include <linux/sfp.h>
+
+struct sfp;
+
+struct sfp_quirk {
+	const char *vendor;
+	const char *part;
+	void (*support)(const struct sfp_eeprom_id *id,
+			struct sfp_module_caps *caps);
+	void (*fixup)(struct sfp *sfp);
+};
+
+struct sfp_socket_ops {
+	void (*attach)(struct sfp *sfp);
+	void (*detach)(struct sfp *sfp);
+	void (*start)(struct sfp *sfp);
+	void (*stop)(struct sfp *sfp);
+	void (*set_signal_rate)(struct sfp *sfp, unsigned int rate_kbd);
+	int (*module_info)(struct sfp *sfp, struct ethtool_modinfo *modinfo);
+	int (*module_eeprom)(struct sfp *sfp, struct ethtool_eeprom *ee,
+			     u8 *data);
+	int (*module_eeprom_by_page)(struct sfp *sfp,
+				     const struct ethtool_module_eeprom *page,
+				     struct netlink_ext_ack *extack);
+};
+
+int sfp_add_phy(struct sfp_bus *bus, struct phy_device *phydev);
+void sfp_remove_phy(struct sfp_bus *bus);
+void sfp_link_up(struct sfp_bus *bus);
+void sfp_link_down(struct sfp_bus *bus);
+int sfp_module_insert(struct sfp_bus *bus, const struct sfp_eeprom_id *id,
+		      const struct sfp_quirk *quirk);
+void sfp_module_remove(struct sfp_bus *bus);
+int sfp_module_start(struct sfp_bus *bus);
+void sfp_module_stop(struct sfp_bus *bus);
+struct sfp_bus *sfp_register_socket(struct device *dev, struct sfp *sfp,
+				    const struct sfp_socket_ops *ops);
+void sfp_unregister_socket(struct sfp_bus *bus);
+
+#endif