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, 49 insertions, 0 deletions

diff --git a/drivers/gpib/include/amcc5920.h b/drivers/gpib/include/amcc5920.h
new file mode 100644
index 000000000..7a88bd282
--- /dev/null
+++ b/drivers/gpib/include/amcc5920.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/***************************************************************************
+ *  Header for amcc5920 pci chip
+ *
+ *   copyright		  : (C) 2002 by Frank Mori Hess
+ ***************************************************************************/
+
+// plx pci chip registers and bits
+enum amcc_registers {
+	AMCC_INTCS_REG = 0x38,
+	AMCC_PASS_THRU_REG	= 0x60,
+};
+
+enum amcc_incsr_bits {
+	AMCC_ADDON_INTR_ENABLE_BIT = 0x2000,
+	AMCC_ADDON_INTR_ACTIVE_BIT = 0x400000,
+	AMCC_INTR_ACTIVE_BIT = 0x800000,
+};
+
+static const int bits_per_region = 8;
+
+static inline uint32_t amcc_wait_state_bits(unsigned int region, unsigned int num_wait_states)
+{
+	return (num_wait_states & 0x7) << (--region * bits_per_region);
+};
+
+enum amcc_prefetch_bits {
+	PREFETCH_DISABLED = 0x0,
+	PREFETCH_SMALL = 0x8,
+	PREFETCH_MEDIUM = 0x10,
+	PREFETCH_LARGE = 0x18,
+};
+
+static inline uint32_t amcc_prefetch_bits(unsigned int region, enum amcc_prefetch_bits prefetch)
+{
+	return prefetch << (--region * bits_per_region);
+};
+
+static inline uint32_t amcc_PTADR_mode_bit(unsigned int region)
+{
+	return 0x80 << (--region * bits_per_region);
+};
+
+static inline uint32_t amcc_disable_write_fifo_bit(unsigned int region)
+{
+	return 0x20 << (--region * bits_per_region);
+};
+