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, 44 insertions, 0 deletions

diff --git a/drivers/fwctl/Kconfig b/drivers/fwctl/Kconfig
new file mode 100644
index 000000000..d1b1925bd
--- /dev/null
+++ b/drivers/fwctl/Kconfig
@@ -0,0 +1,44 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menuconfig FWCTL
+	tristate "fwctl device firmware access framework"
+	help
+	  fwctl provides a userspace API for restricted access to communicate
+	  with on-device firmware. The communication channel is intended to
+	  support a wide range of lockdown compatible device behaviors including
+	  manipulating device FLASH, debugging, and other activities that don't
+	  fit neatly into an existing subsystem.
+
+if FWCTL
+config FWCTL_BNXT
+	tristate "bnxt control fwctl driver"
+	depends on BNXT
+	help
+	  BNXT provides interface for the user process to access the debug and
+	  configuration registers of the Broadcom NIC hardware family.
+	  This will allow configuration and debug tools to work out of the box on
+	  mainstream kernel.
+
+	  If you don't know what to do here, say N.
+
+config FWCTL_MLX5
+	tristate "mlx5 ConnectX control fwctl driver"
+	depends on MLX5_CORE
+	help
+	  MLX5 provides interface for the user process to access the debug and
+	  configuration registers of the ConnectX hardware family
+	  (NICs, PCI switches and SmartNIC SoCs).
+	  This will allow configuration and debug tools to work out of the box on
+	  mainstream kernel.
+
+	  If you don't know what to do here, say N.
+
+config FWCTL_PDS
+	tristate "AMD/Pensando pds fwctl driver"
+	depends on PDS_CORE
+	help
+	  The pds_fwctl driver provides an fwctl interface for a user process
+	  to access the debug and configuration information of the AMD/Pensando
+	  DSC hardware family.
+
+	  If you don't know what to do here, say N.
+endif