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, 36 insertions, 0 deletions

diff --git a/block/partitions/atari.h b/block/partitions/atari.h
new file mode 100644
index 000000000..678202442
--- /dev/null
+++ b/block/partitions/atari.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ *  fs/partitions/atari.h
+ *  Moved by Russell King from:
+ *
+ * linux/include/linux/atari_rootsec.h
+ * definitions for Atari Rootsector layout
+ * by Andreas Schwab (schwab@ls5.informatik.uni-dortmund.de)
+ *
+ * modified for ICD/Supra partitioning scheme restricted to at most 12
+ * partitions
+ * by Guenther Kelleter (guenther@pool.informatik.rwth-aachen.de)
+ */
+
+#include <linux/compiler.h>
+
+struct partition_info
+{
+  u8 flg;			/* bit 0: active; bit 7: bootable */
+  char id[3];			/* "GEM", "BGM", "XGM", or other */
+  __be32 st;			/* start of partition */
+  __be32 siz;			/* length of partition */
+};
+
+struct rootsector
+{
+  char unused[0x156];		/* room for boot code */
+  struct partition_info icdpart[8];	/* info for ICD-partitions 5..12 */
+  char unused2[0xc];
+  u32 hd_siz;			/* size of disk in blocks */
+  struct partition_info part[4];
+  u32 bsl_st;			/* start of bad sector list */
+  u32 bsl_cnt;			/* length of bad sector list */
+  u16 checksum;			/* checksum for bootable disks */
+} __packed;
+