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, 61 insertions, 0 deletions

diff --git a/include/uapi/video/uvesafb.h b/include/uapi/video/uvesafb.h
new file mode 100644
index 000000000..a0d5c9213
--- /dev/null
+++ b/include/uapi/video/uvesafb.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_UVESAFB_H
+#define _UAPI_UVESAFB_H
+
+#include <linux/types.h>
+
+struct v86_regs {
+	__u32 ebx;
+	__u32 ecx;
+	__u32 edx;
+	__u32 esi;
+	__u32 edi;
+	__u32 ebp;
+	__u32 eax;
+	__u32 eip;
+	__u32 eflags;
+	__u32 esp;
+	__u16 cs;
+	__u16 ss;
+	__u16 es;
+	__u16 ds;
+	__u16 fs;
+	__u16 gs;
+};
+
+/* Task flags */
+#define TF_VBEIB	0x01
+#define TF_BUF_ESDI	0x02
+#define TF_BUF_ESBX	0x04
+#define TF_BUF_RET	0x08
+#define TF_EXIT		0x10
+
+struct uvesafb_task {
+	__u8 flags;
+	int buf_len;
+	struct v86_regs regs;
+};
+
+/* Constants for the capabilities field
+ * in vbe_ib */
+#define VBE_CAP_CAN_SWITCH_DAC	0x01
+#define VBE_CAP_VGACOMPAT	0x02
+
+/* The VBE Info Block */
+struct vbe_ib {
+	char  vbe_signature[4];
+	__u16 vbe_version;
+	__u32 oem_string_ptr;
+	__u32 capabilities;
+	__u32 mode_list_ptr;
+	__u16 total_memory;
+	__u16 oem_software_rev;
+	__u32 oem_vendor_name_ptr;
+	__u32 oem_product_name_ptr;
+	__u32 oem_product_rev_ptr;
+	__u8  reserved[222];
+	char  oem_data[256];
+	char  misc_data[512];
+} __attribute__ ((packed));
+
+#endif /* _UAPI_UVESAFB_H */