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, 78 insertions, 0 deletions

diff --git a/drivers/thunderbolt/Kconfig b/drivers/thunderbolt/Kconfig
new file mode 100644
index 000000000..294b3227a
--- /dev/null
+++ b/drivers/thunderbolt/Kconfig
@@ -0,0 +1,78 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menuconfig USB4
+	tristate "Unified support for USB4 and Thunderbolt"
+	depends on PCI
+	select APPLE_PROPERTIES if EFI_STUB && X86
+	select CRC32
+	select CRYPTO_LIB_SHA256
+	select CRYPTO_LIB_UTILS
+	select NVMEM
+	help
+	  USB4 and Thunderbolt driver. USB4 is the public specification
+	  based on the Thunderbolt 3 protocol. This driver is required if
+	  you want to hotplug Thunderbolt and USB4 compliant devices on
+	  Apple hardware or on PCs with Intel Falcon Ridge or newer.
+
+	  To compile this driver a module, choose M here. The module will be
+	  called thunderbolt.
+
+if USB4
+
+config USB4_CONFIGFS
+	def_tristate USB4
+	depends on CONFIGFS_FS && !(USB4=y && CONFIGFS_FS=m)
+
+config USB4_DEBUGFS_WRITE
+	bool "Enable write by debugfs to configuration spaces (DANGEROUS)"
+	help
+	  Enables writing to device configuration registers through
+	  debugfs interface. You can use tools such as Thunderbolt/USB4
+	  debugging tools to access these registers. For more
+	  information see:
+
+	    https://github.com/intel/tbtools
+
+	  Only enable this if you know what you are doing! Never enable
+	  this for production systems or distro kernels.
+
+config USB4_DEBUGFS_MARGINING
+	bool "Expose receiver lane margining operations under USB4 ports and retimers (DANGEROUS)"
+	depends on DEBUG_FS
+	depends on USB4_DEBUGFS_WRITE
+	help
+	  Enables hardware and software based receiver lane margining
+	  support under each USB4 port and retimer, including retimers
+	  on the other side of the cable. Used for electrical quality
+	  and robustness validation during manufacturing. Should not be
+	  enabled by distro kernels.
+
+config USB4_KUNIT_TEST
+	bool "KUnit tests" if !KUNIT_ALL_TESTS
+	depends on USB4 && KUNIT=y
+	default KUNIT_ALL_TESTS
+
+config USB4_DMA_TEST
+	tristate "DMA traffic test driver"
+	depends on DEBUG_FS
+	help
+	  This allows sending and receiving DMA traffic through loopback
+	  connection. Loopback connection can be done by either special
+	  dongle that has TX/RX lines crossed, or by simply connecting a
+	  cable back to the host. Only enable this if you know what you
+	  are doing. Normal users and distro kernels should say N here.
+
+	  To compile this driver a module, choose M here. The module will be
+	  called thunderbolt_dma_test.
+
+config USB4_STREAM
+	tristate "Stream data over Thunderbolt/USB4 cable"
+	depends on USB4_CONFIGFS
+	help
+	  This adds support for USB4STREAM protocol that allows two
+	  hosts to stream data directly over Thunderbolt/USB4 cable
+	  through /dev/tbstreamX devices.
+
+	  To compile this driver a module, choose M here. The module will be
+	  called thunderbolt_stream.
+
+endif # USB4