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, 219 insertions, 0 deletions

diff --git a/include/drm/drm_of.h b/include/drm/drm_of.h
new file mode 100644
index 000000000..7bcc0ccfe
--- /dev/null
+++ b/include/drm/drm_of.h
@@ -0,0 +1,219 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __DRM_OF_H__
+#define __DRM_OF_H__
+
+#include <linux/err.h>
+#include <linux/of_graph.h>
+#if IS_ENABLED(CONFIG_OF) && IS_ENABLED(CONFIG_DRM_PANEL_BRIDGE)
+#include <linux/of.h>
+#include <drm/drm_bridge.h>
+#endif
+
+struct component_master_ops;
+struct component_match;
+struct device;
+struct drm_device;
+struct drm_encoder;
+struct drm_panel;
+struct drm_bridge;
+struct device_node;
+struct mipi_dsi_device_info;
+struct mipi_dsi_host;
+
+/**
+ * enum drm_lvds_dual_link_pixels - Pixel order of an LVDS dual-link connection
+ * @DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS: Even pixels are expected to be generated
+ *    from the first port, odd pixels from the second port
+ * @DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS: Odd pixels are expected to be generated
+ *    from the first port, even pixels from the second port
+ */
+enum drm_lvds_dual_link_pixels {
+	DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS = 0,
+	DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS = 1,
+};
+
+#ifdef CONFIG_OF
+uint32_t drm_of_crtc_port_mask(struct drm_device *dev,
+			    struct device_node *port);
+uint32_t drm_of_find_possible_crtcs(struct drm_device *dev,
+				    struct device_node *port);
+void drm_of_component_match_add(struct device *master,
+				struct component_match **matchptr,
+				int (*compare)(struct device *, void *),
+				struct device_node *node);
+int drm_of_component_probe(struct device *dev,
+			   int (*compare_of)(struct device *, void *),
+			   const struct component_master_ops *m_ops);
+int drm_of_encoder_active_endpoint(struct device_node *node,
+				   struct drm_encoder *encoder,
+				   struct of_endpoint *endpoint);
+int drm_of_find_panel_or_bridge(const struct device_node *np,
+				int port, int endpoint,
+				struct drm_panel **panel,
+				struct drm_bridge **bridge);
+int drm_of_lvds_get_dual_link_pixel_order(const struct device_node *port1,
+					  const struct device_node *port2);
+int drm_of_lvds_get_dual_link_pixel_order_sink(struct device_node *port1,
+					       struct device_node *port2);
+int drm_of_lvds_get_data_mapping(const struct device_node *port);
+int drm_of_get_data_lanes_count(const struct device_node *endpoint,
+				const unsigned int min, const unsigned int max);
+int drm_of_get_data_lanes_count_ep(const struct device_node *port,
+				   int port_reg, int reg,
+				   const unsigned int min,
+				   const unsigned int max);
+int drm_of_get_data_lanes_count_remote(const struct device_node *port,
+				       int port_reg, int reg,
+				       const unsigned int min,
+				       const unsigned int max);
+#else
+static inline uint32_t drm_of_crtc_port_mask(struct drm_device *dev,
+					  struct device_node *port)
+{
+	return 0;
+}
+
+static inline uint32_t drm_of_find_possible_crtcs(struct drm_device *dev,
+						  struct device_node *port)
+{
+	return 0;
+}
+
+static inline void
+drm_of_component_match_add(struct device *master,
+			   struct component_match **matchptr,
+			   int (*compare)(struct device *, void *),
+			   struct device_node *node)
+{
+}
+
+static inline int
+drm_of_component_probe(struct device *dev,
+		       int (*compare_of)(struct device *, void *),
+		       const struct component_master_ops *m_ops)
+{
+	return -EINVAL;
+}
+
+static inline int drm_of_encoder_active_endpoint(struct device_node *node,
+						 struct drm_encoder *encoder,
+						 struct of_endpoint *endpoint)
+{
+	return -EINVAL;
+}
+static inline int drm_of_find_panel_or_bridge(const struct device_node *np,
+					      int port, int endpoint,
+					      struct drm_panel **panel,
+					      struct drm_bridge **bridge)
+{
+	return -EINVAL;
+}
+
+static inline int
+drm_of_lvds_get_dual_link_pixel_order(const struct device_node *port1,
+				      const struct device_node *port2)
+{
+	return -EINVAL;
+}
+
+static inline int
+drm_of_lvds_get_dual_link_pixel_order_sink(struct device_node *port1,
+					   struct device_node *port2)
+{
+	return -EINVAL;
+}
+
+static inline int
+drm_of_lvds_get_data_mapping(const struct device_node *port)
+{
+	return -EINVAL;
+}
+
+static inline int
+drm_of_get_data_lanes_count(const struct device_node *endpoint,
+			    const unsigned int min, const unsigned int max)
+{
+	return -EINVAL;
+}
+
+static inline int
+drm_of_get_data_lanes_count_ep(const struct device_node *port,
+			       int port_reg, int reg,
+			       const unsigned int min,
+			       const unsigned int max)
+{
+	return -EINVAL;
+}
+
+static inline int
+drm_of_get_data_lanes_count_remote(const struct device_node *port,
+				   int port_reg, int reg,
+				   const unsigned int min,
+				   const unsigned int max)
+{
+	return -EINVAL;
+}
+#endif
+
+#if IS_ENABLED(CONFIG_OF) && IS_ENABLED(CONFIG_DRM_MIPI_DSI)
+struct mipi_dsi_host *drm_of_get_dsi_bus(struct device *dev);
+#else
+static inline struct
+mipi_dsi_host *drm_of_get_dsi_bus(struct device *dev)
+{
+	return ERR_PTR(-EINVAL);
+}
+#endif /* CONFIG_OF && CONFIG_DRM_MIPI_DSI */
+
+/*
+ * drm_of_panel_bridge_remove - remove panel bridge
+ * @np: device tree node containing panel bridge output ports
+ *
+ * Remove the panel bridge of a given DT node's port and endpoint number
+ *
+ * Returns zero if successful, or one of the standard error codes if it fails.
+ */
+static inline int drm_of_panel_bridge_remove(const struct device_node *np,
+					     int port, int endpoint)
+{
+#if IS_ENABLED(CONFIG_OF) && IS_ENABLED(CONFIG_DRM_PANEL_BRIDGE)
+	struct drm_bridge *bridge;
+	struct device_node *remote;
+
+	remote = of_graph_get_remote_node(np, port, endpoint);
+	if (!remote)
+		return -ENODEV;
+
+	bridge = of_drm_find_and_get_bridge(remote);
+	drm_panel_bridge_remove(bridge);
+
+	drm_bridge_put(bridge);
+	of_node_put(remote);
+
+	return 0;
+#else
+	return -EINVAL;
+#endif
+}
+
+static inline int drm_of_encoder_active_endpoint_id(struct device_node *node,
+						    struct drm_encoder *encoder)
+{
+	struct of_endpoint endpoint;
+	int ret = drm_of_encoder_active_endpoint(node, encoder,
+						 &endpoint);
+
+	return ret ?: endpoint.id;
+}
+
+static inline int drm_of_encoder_active_port_id(struct device_node *node,
+						struct drm_encoder *encoder)
+{
+	struct of_endpoint endpoint;
+	int ret = drm_of_encoder_active_endpoint(node, encoder,
+						 &endpoint);
+
+	return ret ?: endpoint.port;
+}
+
+#endif /* __DRM_OF_H__ */