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, 302 insertions, 0 deletions

diff --git a/include/rdma/ib_umem.h b/include/rdma/ib_umem.h
new file mode 100644
index 000000000..31b3a86fe
--- /dev/null
+++ b/include/rdma/ib_umem.h
@@ -0,0 +1,302 @@
+/* SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB */
+/*
+ * Copyright (c) 2007 Cisco Systems.  All rights reserved.
+ * Copyright (c) 2020 Intel Corporation.  All rights reserved.
+ */
+
+#ifndef IB_UMEM_H
+#define IB_UMEM_H
+
+#include <linux/scatterlist.h>
+
+struct ib_device;
+struct dma_buf_attach_ops;
+
+struct ib_umem {
+	struct ib_device       *ibdev;
+	struct mm_struct       *owning_mm;
+	u64 iova;
+	size_t			length;
+	unsigned long		address;
+	unsigned long		dma_attrs;
+	u32 writable : 1;
+	u32 is_odp : 1;
+	u32 is_dmabuf : 1;
+	struct sg_append_table sgt_append;
+};
+
+struct ib_umem_dmabuf {
+	struct ib_umem umem;
+	struct dma_buf_attachment *attach;
+	struct sg_table *sgt;
+	struct scatterlist *first_sg;
+	struct scatterlist *last_sg;
+	unsigned long first_sg_offset;
+	unsigned long last_sg_trim;
+	void (*pinned_revoke)(void *priv);
+	void *private;
+	u8 pinned : 1;
+	u8 revoked : 1;
+};
+
+static inline struct ib_umem_dmabuf *to_ib_umem_dmabuf(struct ib_umem *umem)
+{
+	return container_of(umem, struct ib_umem_dmabuf, umem);
+}
+
+/* Returns the offset of the umem start relative to the first page. */
+static inline int ib_umem_offset(struct ib_umem *umem)
+{
+	return umem->address & ~PAGE_MASK;
+}
+
+static inline dma_addr_t ib_umem_start_dma_addr(struct ib_umem *umem)
+{
+	return sg_dma_address(umem->sgt_append.sgt.sgl) + ib_umem_offset(umem);
+}
+
+static inline unsigned long ib_umem_dma_offset(struct ib_umem *umem,
+					       unsigned long pgsz)
+{
+	return ib_umem_start_dma_addr(umem) & (pgsz - 1);
+}
+
+static inline size_t ib_umem_num_dma_blocks(struct ib_umem *umem,
+					    unsigned long pgsz)
+{
+	return (size_t)((ALIGN(umem->iova + umem->length, pgsz) -
+			 ALIGN_DOWN(umem->iova, pgsz))) /
+	       pgsz;
+}
+
+static inline size_t ib_umem_num_pages(struct ib_umem *umem)
+{
+	return ib_umem_num_dma_blocks(umem, PAGE_SIZE);
+}
+
+struct ib_udata;
+struct ib_uverbs_buffer_desc;
+struct uverbs_attr_bundle;
+
+#ifdef CONFIG_INFINIBAND_USER_MEM
+
+struct ib_umem *ib_umem_get_desc(struct ib_device *device,
+				 const struct ib_uverbs_buffer_desc *desc,
+				 int access);
+struct ib_umem *ib_umem_get_attr(struct ib_device *device,
+				 const struct uverbs_attr_bundle *attrs,
+				 u16 attr_id, size_t size, int access);
+struct ib_umem *ib_umem_get_attr_or_va(struct ib_device *device,
+				       const struct uverbs_attr_bundle *attrs,
+				       u16 attr_id, u64 addr, size_t size,
+				       int access);
+struct ib_umem *ib_umem_get_cq_buf(struct ib_device *device,
+				   const struct uverbs_attr_bundle *attrs,
+				   size_t size, int access);
+struct ib_umem *ib_umem_get_cq_buf_or_va(struct ib_device *device,
+					 const struct uverbs_attr_bundle *attrs,
+					 u64 addr, size_t size, int access);
+
+static inline struct ib_umem *ib_umem_get_va(struct ib_device *device,
+					     unsigned long addr, size_t size,
+					     int access)
+{
+	return ib_umem_get_attr_or_va(device, NULL, 0, addr, size, access);
+}
+
+void ib_umem_release(struct ib_umem *umem);
+int ib_umem_copy_from(void *dst, struct ib_umem *umem, size_t offset,
+		      size_t length);
+unsigned long ib_umem_find_best_pgsz(struct ib_umem *umem,
+				     unsigned long pgsz_bitmap,
+				     u64 virt);
+
+/**
+ * ib_umem_find_best_pgoff - Find best HW page size
+ *
+ * @umem: umem struct
+ * @pgsz_bitmap: bitmap of HW supported page sizes
+ * @pgoff_bitmask: Mask of bits that can be represented with an offset
+ *
+ * This is very similar to ib_umem_find_best_pgsz() except instead of accepting
+ * an IOVA it accepts a bitmask specifying what address bits can be represented
+ * with a page offset.
+ *
+ * For instance if the HW has multiple page sizes, requires 64 byte alignemnt,
+ * and can support aligned offsets up to 4032 then pgoff_bitmask would be
+ * "111111000000".
+ *
+ * If the pgoff_bitmask requires either alignment in the low bit or an
+ * unavailable page size for the high bits, this function returns 0.
+ *
+ * Returns: best HW page size for the parameters or 0 if none available
+ *   for the given parameters.
+ */
+static inline unsigned long ib_umem_find_best_pgoff(struct ib_umem *umem,
+						    unsigned long pgsz_bitmap,
+						    u64 pgoff_bitmask)
+{
+	dma_addr_t dma_addr;
+
+	dma_addr = ib_umem_start_dma_addr(umem);
+	return ib_umem_find_best_pgsz(umem, pgsz_bitmap,
+				      dma_addr & pgoff_bitmask);
+}
+
+static inline bool ib_umem_is_contiguous(struct ib_umem *umem)
+{
+	unsigned long pgsz;
+
+	pgsz = ib_umem_find_best_pgsz(umem, ULONG_MAX,
+				      ib_umem_start_dma_addr(umem));
+	return pgsz && ib_umem_num_dma_blocks(umem, pgsz) == 1;
+}
+
+struct ib_umem_dmabuf *ib_umem_dmabuf_get(struct ib_device *device,
+					  unsigned long offset, size_t size,
+					  int fd, int access,
+					  const struct dma_buf_attach_ops *ops);
+struct ib_umem_dmabuf *ib_umem_dmabuf_get_pinned(struct ib_device *device,
+						 unsigned long offset,
+						 size_t size, int fd,
+						 int access);
+struct ib_umem_dmabuf *
+ib_umem_dmabuf_get_pinned_revocable_and_lock(struct ib_device *device,
+					     unsigned long offset, size_t size,
+					     int fd, int access);
+void ib_umem_dmabuf_set_revoke_locked(struct ib_umem_dmabuf *umem_dmabuf,
+				      void (*revoke)(void *priv), void *priv);
+struct ib_umem_dmabuf *
+ib_umem_dmabuf_get_pinned_with_dma_device(struct ib_device *device,
+					  struct device *dma_device,
+					  unsigned long offset, size_t size,
+					  int fd, int access);
+int ib_umem_dmabuf_map_pages(struct ib_umem_dmabuf *umem_dmabuf);
+void ib_umem_dmabuf_unmap_pages(struct ib_umem_dmabuf *umem_dmabuf);
+void ib_umem_dmabuf_release(struct ib_umem_dmabuf *umem_dmabuf);
+void ib_umem_dmabuf_revoke_lock(struct ib_umem_dmabuf *umem_dmabuf);
+void ib_umem_dmabuf_revoke_unlock(struct ib_umem_dmabuf *umem_dmabuf);
+void ib_umem_dmabuf_revoke(struct ib_umem_dmabuf *umem_dmabuf);
+
+int ib_umem_check_rereg(struct ib_umem *umem, int flags, int new_access_flags);
+
+#else /* CONFIG_INFINIBAND_USER_MEM */
+
+#include <linux/err.h>
+
+static inline struct ib_umem *
+ib_umem_get_desc(struct ib_device *device,
+		 const struct ib_uverbs_buffer_desc *desc, int access)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+static inline struct ib_umem *ib_umem_get_va(struct ib_device *device,
+					     unsigned long addr, size_t size,
+					     int access)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+static inline struct ib_umem *
+ib_umem_get_attr(struct ib_device *device,
+		 const struct uverbs_attr_bundle *attrs, u16 attr_id,
+		 size_t size, int access)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+static inline struct ib_umem *
+ib_umem_get_attr_or_va(struct ib_device *device,
+		       const struct uverbs_attr_bundle *attrs, u16 attr_id,
+		       u64 addr, size_t size, int access)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+static inline struct ib_umem *
+ib_umem_get_cq_buf(struct ib_device *device,
+		   const struct uverbs_attr_bundle *attrs, size_t size,
+		   int access)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+static inline struct ib_umem *
+ib_umem_get_cq_buf_or_va(struct ib_device *device,
+			 const struct uverbs_attr_bundle *attrs, u64 addr,
+			 size_t size, int access)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+static inline void ib_umem_release(struct ib_umem *umem) { }
+static inline int ib_umem_copy_from(void *dst, struct ib_umem *umem, size_t offset,
+		      		    size_t length) {
+	return -EOPNOTSUPP;
+}
+static inline unsigned long ib_umem_find_best_pgsz(struct ib_umem *umem,
+						   unsigned long pgsz_bitmap,
+						   u64 virt)
+{
+	return 0;
+}
+static inline unsigned long ib_umem_find_best_pgoff(struct ib_umem *umem,
+						    unsigned long pgsz_bitmap,
+						    u64 pgoff_bitmask)
+{
+	return 0;
+}
+static inline bool ib_umem_is_contiguous(struct ib_umem *umem)
+{
+	return false;
+}
+static inline
+struct ib_umem_dmabuf *ib_umem_dmabuf_get(struct ib_device *device,
+					  unsigned long offset,
+					  size_t size, int fd,
+					  int access,
+					  struct dma_buf_attach_ops *ops)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+static inline struct ib_umem_dmabuf *
+ib_umem_dmabuf_get_pinned(struct ib_device *device, unsigned long offset,
+			  size_t size, int fd, int access)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
+static inline struct ib_umem_dmabuf *
+ib_umem_dmabuf_get_pinned_revocable_and_lock(struct ib_device *device,
+					     unsigned long offset, size_t size,
+					     int fd, int access)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
+static inline void
+ib_umem_dmabuf_set_revoke_locked(struct ib_umem_dmabuf *umem_dmabuf,
+				 void (*revoke)(void *priv), void *priv) {}
+
+static inline struct ib_umem_dmabuf *
+ib_umem_dmabuf_get_pinned_with_dma_device(struct ib_device *device,
+					  struct device *dma_device,
+					  unsigned long offset, size_t size,
+					  int fd, int access)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
+static inline int ib_umem_dmabuf_map_pages(struct ib_umem_dmabuf *umem_dmabuf)
+{
+	return -EOPNOTSUPP;
+}
+static inline void ib_umem_dmabuf_unmap_pages(struct ib_umem_dmabuf *umem_dmabuf) { }
+static inline void ib_umem_dmabuf_release(struct ib_umem_dmabuf *umem_dmabuf) { }
+static inline void ib_umem_dmabuf_revoke_lock(struct ib_umem_dmabuf *umem_dmabuf) {}
+static inline void ib_umem_dmabuf_revoke_unlock(struct ib_umem_dmabuf *umem_dmabuf) {}
+static inline void ib_umem_dmabuf_revoke(struct ib_umem_dmabuf *umem_dmabuf) {}
+
+static inline int ib_umem_check_rereg(struct ib_umem *umem, int flags,
+				      int new_access_flags)
+{
+	return -EOPNOTSUPP;
+}
+
+#endif /* CONFIG_INFINIBAND_USER_MEM */
+#endif /* IB_UMEM_H */