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, 119 insertions, 0 deletions

diff --git a/include/drm/drm_prime.h b/include/drm/drm_prime.h
new file mode 100644
index 000000000..f50f862f0
--- /dev/null
+++ b/include/drm/drm_prime.h
@@ -0,0 +1,119 @@
+/*
+ * Copyright © 2012 Red Hat
+ * Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
+ * Copyright 2000 VA Linux Systems, Inc., Sunnyvale, California.
+ * Copyright (c) 2009-2010, Code Aurora Forum.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ * Authors:
+ *      Dave Airlie <airlied@redhat.com>
+ *      Rob Clark <rob.clark@linaro.org>
+ *
+ */
+
+#ifndef __DRM_PRIME_H__
+#define __DRM_PRIME_H__
+
+#include <linux/mutex.h>
+#include <linux/rbtree.h>
+#include <linux/scatterlist.h>
+
+/**
+ * struct drm_prime_file_private - per-file tracking for PRIME
+ *
+ * This just contains the internal &struct dma_buf and handle caches for each
+ * &struct drm_file used by the PRIME core code.
+ */
+struct drm_prime_file_private {
+/* private: */
+	struct mutex lock;
+	struct rb_root dmabufs;
+	struct rb_root handles;
+};
+
+struct device;
+
+struct dma_buf_export_info;
+struct dma_buf;
+struct dma_buf_attachment;
+struct iosys_map;
+
+enum dma_data_direction;
+
+struct drm_device;
+struct drm_gem_object;
+struct drm_file;
+
+/* core prime functions */
+struct dma_buf *drm_gem_dmabuf_export(struct drm_device *dev,
+				      struct dma_buf_export_info *exp_info);
+void drm_gem_dmabuf_release(struct dma_buf *dma_buf);
+
+int drm_gem_prime_fd_to_handle(struct drm_device *dev,
+			       struct drm_file *file_priv, int prime_fd, uint32_t *handle);
+struct dma_buf *drm_gem_prime_handle_to_dmabuf(struct drm_device *dev,
+			       struct drm_file *file_priv, uint32_t handle,
+			       uint32_t flags);
+int drm_gem_prime_handle_to_fd(struct drm_device *dev,
+			       struct drm_file *file_priv, uint32_t handle, uint32_t flags,
+			       int *prime_fd);
+
+/* helper functions for exporting */
+int drm_gem_map_attach(struct dma_buf *dma_buf,
+		       struct dma_buf_attachment *attach);
+void drm_gem_map_detach(struct dma_buf *dma_buf,
+			struct dma_buf_attachment *attach);
+struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
+				     enum dma_data_direction dir);
+void drm_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
+			   struct sg_table *sgt,
+			   enum dma_data_direction dir);
+int drm_gem_dmabuf_vmap(struct dma_buf *dma_buf, struct iosys_map *map);
+void drm_gem_dmabuf_vunmap(struct dma_buf *dma_buf, struct iosys_map *map);
+
+int drm_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma);
+int drm_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *vma);
+
+struct sg_table *drm_prime_pages_to_sg(struct drm_device *dev,
+				       struct page **pages, unsigned int nr_pages);
+struct dma_buf *drm_gem_prime_export(struct drm_gem_object *obj,
+				     int flags);
+
+unsigned long drm_prime_get_contiguous_size(struct sg_table *sgt);
+
+/* helper functions for importing */
+bool drm_gem_is_prime_exported_dma_buf(struct drm_device *dev,
+				       struct dma_buf *dma_buf);
+
+struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
+						struct dma_buf *dma_buf,
+						struct device *attach_dev);
+struct drm_gem_object *drm_gem_prime_import(struct drm_device *dev,
+					    struct dma_buf *dma_buf);
+
+void drm_prime_gem_destroy(struct drm_gem_object *obj, struct sg_table *sg);
+
+int drm_prime_sg_to_page_array(struct sg_table *sgt, struct page **pages,
+			       int max_pages);
+int drm_prime_sg_to_dma_addr_array(struct sg_table *sgt, dma_addr_t *addrs,
+				   int max_pages);
+
+#endif /* __DRM_PRIME_H__ */