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, 96 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-switchtec b/Documentation/ABI/testing/sysfs-class-switchtec
new file mode 100644
index 000000000..76c7a661a
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-switchtec
@@ -0,0 +1,96 @@
+switchtec - Microsemi Switchtec PCI Switch Management Endpoint
+
+For details on this subsystem look at Documentation/driver-api/switchtec.rst.
+
+What: 		/sys/class/switchtec
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	The switchtec class subsystem folder.
+		Each registered switchtec driver is represented by a switchtecX
+		subfolder (X being an integer >= 0).
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/component_id
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Component identifier as stored in the hardware (eg. PM8543)
+		(read only)
+Values: 	arbitrary string.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/component_revision
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Component revision stored in the hardware (read only)
+Values: 	integer.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/component_vendor
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Component vendor as stored in the hardware (eg. MICROSEM)
+		(read only)
+Values: 	arbitrary string.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/device_version
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Device version as stored in the hardware (read only)
+Values: 	integer.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/fw_version
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Currently running firmware version (read only)
+Values: 	integer (in hexadecimal).
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/partition
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Partition number for this device in the switch (read only)
+Values: 	integer.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/partition_count
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Total number of partitions in the switch (read only)
+Values: 	integer.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/product_id
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Product identifier as stored in the hardware (eg. PSX 48XG3)
+		(read only)
+Values: 	arbitrary string.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/product_revision
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Product revision stored in the hardware (eg. RevB)
+		(read only)
+Values: 	arbitrary string.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/product_vendor
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Product vendor as stored in the hardware (eg. MICROSEM)
+		(read only)
+Values: 	arbitrary string.