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, 59 insertions, 0 deletions

diff --git a/drivers/gpib/include/amccs5933.h b/drivers/gpib/include/amccs5933.h
new file mode 100644
index 000000000..d7f63c795
--- /dev/null
+++ b/drivers/gpib/include/amccs5933.h
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/***************************************************************************
+ * Registers and bits for amccs5933 pci chip
+ *    copyright            : (C) 2002 by Frank Mori Hess
+ ***************************************************************************/
+
+// register offsets
+enum {
+	MBEF_REG = 0x34,	// mailbux empty/full
+	INTCSR_REG = 0x38,	// interrupt control and status
+	BMCSR_REG = 0x3c,	// bus master control and status
+};
+
+// incoming mailbox 0-3  register offsets
+extern inline int INCOMING_MAILBOX_REG(unsigned int mailbox)
+{
+	return (0x10 + 4 * mailbox);
+};
+
+// bit definitions
+
+// INTCSR bits
+enum {
+	OUTBOX_EMPTY_INTR_BIT = 0x10,	// enable outbox empty interrupt
+	INBOX_FULL_INTR_BIT = 0x1000,	// enable inbox full interrupt
+	INBOX_INTR_CS_BIT = 0x20000,	// read, or write clear inbox full interrupt
+	INTR_ASSERTED_BIT = 0x800000,	// read only, interrupt asserted
+};
+
+// select byte 0 to 3 of incoming mailbox
+extern inline int INBOX_BYTE_BITS(unsigned int byte)
+{
+	return (byte & 0x3) << 8;
+};
+
+// select incoming mailbox 0 to 3
+extern inline int INBOX_SELECT_BITS(unsigned int mailbox)
+{
+	return (mailbox & 0x3) << 10;
+};
+
+// select byte 0 to 3 of outgoing mailbox
+extern inline int OUTBOX_BYTE_BITS(unsigned int byte)
+{
+	return (byte & 0x3);
+};
+
+// select outgoing mailbox 0 to 3
+extern inline int OUTBOX_SELECT_BITS(unsigned int mailbox)
+{
+	return (mailbox & 0x3) << 2;
+};
+
+// BMCSR bits
+enum {
+	MBOX_FLAGS_RESET_BIT = 0x08000000,	// resets mailbox empty/full flags
+};
+