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, 62 insertions, 0 deletions

diff --git a/include/uapi/fwctl/pds.h b/include/uapi/fwctl/pds.h
new file mode 100644
index 000000000..66be32411
--- /dev/null
+++ b/include/uapi/fwctl/pds.h
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/* Copyright(c) Advanced Micro Devices, Inc */
+
+/*
+ * fwctl interface info for pds_fwctl
+ */
+
+#ifndef _UAPI_FWCTL_PDS_H_
+#define _UAPI_FWCTL_PDS_H_
+
+#include <linux/types.h>
+
+/**
+ * struct fwctl_info_pds
+ * @uctx_caps:  bitmap of firmware capabilities
+ *
+ * Return basic information about the FW interface available.
+ */
+struct fwctl_info_pds {
+	__u32 uctx_caps;
+};
+
+/**
+ * enum pds_fwctl_capabilities
+ * @PDS_FWCTL_QUERY_CAP: firmware can be queried for information
+ * @PDS_FWCTL_SEND_CAP:  firmware can be sent commands
+ */
+enum pds_fwctl_capabilities {
+	PDS_FWCTL_QUERY_CAP = 0,
+	PDS_FWCTL_SEND_CAP,
+};
+
+/**
+ * struct fwctl_rpc_pds
+ * @in.op:       requested operation code
+ * @in.ep:       firmware endpoint to operate on
+ * @in.rsvd:     reserved
+ * @in.len:      length of payload data
+ * @in.payload:  address of payload buffer
+ * @in:          rpc in parameters
+ * @out.retval:  operation result value
+ * @out.rsvd:    reserved
+ * @out.len:     length of result data buffer
+ * @out.payload: address of payload data buffer
+ * @out:         rpc out parameters
+ */
+struct fwctl_rpc_pds {
+	struct {
+		__u32 op;
+		__u32 ep;
+		__u32 rsvd;
+		__u32 len;
+		__aligned_u64 payload;
+	} in;
+	struct {
+		__u32 retval;
+		__u32 rsvd[2];
+		__u32 len;
+		__aligned_u64 payload;
+	} out;
+};
+#endif /* _UAPI_FWCTL_PDS_H_ */