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, 166 insertions, 0 deletions

diff --git a/include/media/cec-notifier.h b/include/media/cec-notifier.h
new file mode 100644
index 000000000..b1c839734
--- /dev/null
+++ b/include/media/cec-notifier.h
@@ -0,0 +1,166 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * cec-notifier.h - notify CEC drivers of physical address changes
+ *
+ * Copyright 2016 Russell King.
+ * Copyright 2016-2017 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
+ */
+
+#ifndef LINUX_CEC_NOTIFIER_H
+#define LINUX_CEC_NOTIFIER_H
+
+#include <linux/err.h>
+#include <media/cec.h>
+
+struct device;
+struct edid;
+struct cec_adapter;
+struct cec_notifier;
+
+#if IS_REACHABLE(CONFIG_CEC_CORE) && IS_ENABLED(CONFIG_CEC_NOTIFIER)
+
+/**
+ * cec_notifier_conn_register - find or create a new cec_notifier for the given
+ * HDMI device and connector tuple.
+ * @hdmi_dev: HDMI device that sends the events.
+ * @port_name: the connector name from which the event occurs. May be NULL
+ * if there is always only one HDMI connector created by the HDMI device.
+ * @conn_info: the connector info from which the event occurs (may be NULL)
+ *
+ * If a notifier for device @dev and connector @port_name already exists, then
+ * increase the refcount and return that notifier.
+ *
+ * If it doesn't exist, then allocate a new notifier struct and return a
+ * pointer to that new struct.
+ *
+ * Return NULL if the memory could not be allocated.
+ */
+struct cec_notifier *
+cec_notifier_conn_register(struct device *hdmi_dev, const char *port_name,
+			   const struct cec_connector_info *conn_info);
+
+/**
+ * cec_notifier_conn_unregister - decrease refcount and delete when the
+ * refcount reaches 0.
+ * @n: notifier. If NULL, then this function does nothing.
+ */
+void cec_notifier_conn_unregister(struct cec_notifier *n);
+
+/**
+ * cec_notifier_cec_adap_register - find or create a new cec_notifier for the
+ * given device.
+ * @hdmi_dev: HDMI device that sends the events.
+ * @port_name: the connector name from which the event occurs. May be NULL
+ * if there is always only one HDMI connector created by the HDMI device.
+ * @adap: the cec adapter that registered this notifier.
+ *
+ * If a notifier for device @dev and connector @port_name already exists, then
+ * increase the refcount and return that notifier.
+ *
+ * If it doesn't exist, then allocate a new notifier struct and return a
+ * pointer to that new struct.
+ *
+ * Return NULL if the memory could not be allocated.
+ */
+struct cec_notifier *
+cec_notifier_cec_adap_register(struct device *hdmi_dev, const char *port_name,
+			       struct cec_adapter *adap);
+
+/**
+ * cec_notifier_cec_adap_unregister - decrease refcount and delete when the
+ * refcount reaches 0.
+ * @n: notifier. If NULL, then this function does nothing.
+ * @adap: the cec adapter that registered this notifier.
+ */
+void cec_notifier_cec_adap_unregister(struct cec_notifier *n,
+				      struct cec_adapter *adap);
+
+/**
+ * cec_notifier_set_phys_addr - set a new physical address.
+ * @n: the CEC notifier
+ * @pa: the CEC physical address
+ *
+ * Set a new CEC physical address.
+ * Does nothing if @n == NULL.
+ */
+void cec_notifier_set_phys_addr(struct cec_notifier *n, u16 pa);
+
+/**
+ * cec_notifier_set_phys_addr_from_edid - set parse the PA from the EDID.
+ * @n: the CEC notifier
+ * @edid: the struct edid pointer
+ *
+ * Parses the EDID to obtain the new CEC physical address and set it.
+ * Does nothing if @n == NULL.
+ */
+void cec_notifier_set_phys_addr_from_edid(struct cec_notifier *n,
+					  const struct edid *edid);
+
+/**
+ * cec_notifier_parse_hdmi_phandle - find the hdmi device from "hdmi-phandle"
+ * @dev: the device with the "hdmi-phandle" device tree property
+ *
+ * Returns the device pointer referenced by the "hdmi-phandle" property.
+ * Note that the refcount of the returned device is not incremented.
+ * This device pointer is only used as a key value in the notifier
+ * list, but it is never accessed by the CEC driver.
+ */
+struct device *cec_notifier_parse_hdmi_phandle(struct device *dev);
+
+#else
+
+static inline struct cec_notifier *
+cec_notifier_conn_register(struct device *hdmi_dev, const char *port_name,
+			   const struct cec_connector_info *conn_info)
+{
+	/* A non-NULL pointer is expected on success */
+	return (struct cec_notifier *)0xdeadfeed;
+}
+
+static inline void cec_notifier_conn_unregister(struct cec_notifier *n)
+{
+}
+
+static inline struct cec_notifier *
+cec_notifier_cec_adap_register(struct device *hdmi_dev, const char *port_name,
+			       struct cec_adapter *adap)
+{
+	/* A non-NULL pointer is expected on success */
+	return (struct cec_notifier *)0xdeadfeed;
+}
+
+static inline void cec_notifier_cec_adap_unregister(struct cec_notifier *n,
+						    struct cec_adapter *adap)
+{
+}
+
+static inline void cec_notifier_set_phys_addr(struct cec_notifier *n, u16 pa)
+{
+}
+
+static inline void cec_notifier_set_phys_addr_from_edid(struct cec_notifier *n,
+							const struct edid *edid)
+{
+}
+
+static inline struct device *cec_notifier_parse_hdmi_phandle(struct device *dev)
+{
+	return ERR_PTR(-ENODEV);
+}
+
+#endif
+
+/**
+ * cec_notifier_phys_addr_invalidate() - set the physical address to INVALID
+ *
+ * @n: the CEC notifier
+ *
+ * This is a simple helper function to invalidate the physical
+ * address. Does nothing if @n == NULL.
+ */
+static inline void cec_notifier_phys_addr_invalidate(struct cec_notifier *n)
+{
+	cec_notifier_set_phys_addr(n, CEC_PHYS_ADDR_INVALID);
+}
+
+#endif