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, 41 insertions, 0 deletions

diff --git a/include/drm/intel/intel-gtt.h b/include/drm/intel/intel-gtt.h
new file mode 100644
index 000000000..f53bcff01
--- /dev/null
+++ b/include/drm/intel/intel-gtt.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Common header for intel-gtt.ko and i915.ko */
+
+#ifndef _DRM_INTEL_GTT_H
+#define	_DRM_INTEL_GTT_H
+
+#include <linux/types.h>
+
+struct agp_bridge_data;
+struct pci_dev;
+struct sg_table;
+
+void intel_gmch_gtt_get(u64 *gtt_total,
+			phys_addr_t *mappable_base,
+			resource_size_t *mappable_end);
+
+int intel_gmch_probe(struct pci_dev *bridge_pdev, struct pci_dev *gpu_pdev,
+		     struct agp_bridge_data *bridge);
+void intel_gmch_remove(void);
+
+bool intel_gmch_enable_gtt(void);
+
+void intel_gmch_gtt_flush(void);
+void intel_gmch_gtt_insert_page(dma_addr_t addr,
+				unsigned int pg,
+				unsigned int flags);
+void intel_gmch_gtt_insert_sg_entries(struct sg_table *st,
+				      unsigned int pg_start,
+				      unsigned int flags);
+void intel_gmch_gtt_clear_range(unsigned int first_entry, unsigned int num_entries);
+dma_addr_t intel_gmch_gtt_read_entry(unsigned int pg,
+				     bool *is_present, bool *is_local);
+
+/* Special gtt memory types */
+#define AGP_DCACHE_MEMORY	1
+#define AGP_PHYS_MEMORY		2
+
+/* flag for GFDT type */
+#define AGP_USER_CACHED_MEMORY_GFDT (1 << 3)
+
+#endif