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, 121 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-bus-cdx b/Documentation/ABI/testing/sysfs-bus-cdx
new file mode 100644
index 000000000..e84277531
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-cdx
@@ -0,0 +1,121 @@
+What:		/sys/bus/cdx/rescan
+Date:		March 2023
+Contact:	nipun.gupta@amd.com
+Description:
+		Writing y/1/on to this file will cause rescan of the bus
+		and devices on the CDX bus. Any new devices are scanned and
+		added to the list of Linux devices and any devices removed are
+		also deleted from Linux.
+
+		For example::
+
+		  # echo 1 > /sys/bus/cdx/rescan
+
+What:		/sys/bus/cdx/devices/.../vendor
+Date:		March 2023
+Contact:	nipun.gupta@amd.com
+Description:
+		Vendor ID for this CDX device, in hexadecimal. Vendor ID is
+		16 bit identifier which is specific to the device manufacturer.
+		Combination of Vendor ID and Device ID identifies a device.
+
+What:		/sys/bus/cdx/devices/.../device
+Date:		March 2023
+Contact:	nipun.gupta@amd.com
+Description:
+		Device ID for this CDX device, in hexadecimal. Device ID is
+		16 bit identifier to identify a device type within the range
+		of a device manufacturer.
+		Combination of Vendor ID and Device ID identifies a device.
+
+What:		/sys/bus/cdx/devices/.../subsystem_vendor
+Date:		July 2023
+Contact:	puneet.gupta@amd.com
+Description:
+		Subsystem Vendor ID for this CDX device, in hexadecimal.
+		Subsystem Vendor ID is 16 bit identifier specific to the
+		card manufacturer.
+
+What:		/sys/bus/cdx/devices/.../subsystem_device
+Date:		July 2023
+Contact:	puneet.gupta@amd.com
+Description:
+		Subsystem Device ID for this CDX device, in hexadecimal
+		Subsystem Device ID is 16 bit identifier specific to the
+		card manufacturer.
+
+What:		/sys/bus/cdx/devices/.../class
+Date:		July 2023
+Contact:	puneet.gupta@amd.com
+Description:
+		This file contains the class of the CDX device, in hexadecimal.
+		Class is 24 bit identifier specifies the functionality of the device.
+
+What:		/sys/bus/cdx/devices/.../revision
+Date:		July 2023
+Contact:	puneet.gupta@amd.com
+Description:
+		This file contains the revision field of the CDX device, in hexadecimal.
+		Revision is 8 bit revision identifier of the device.
+
+What:		/sys/bus/cdx/devices/.../enable
+Date:		October 2023
+Contact:	abhijit.gangurde@amd.com
+Description:
+		CDX bus should be disabled before updating the devices in FPGA.
+		Writing n/0/off will attempt to disable the CDX bus and.
+		writing y/1/on will attempt to enable the CDX bus. Reading this file
+		gives the current state of the bus, 1 for enabled and 0 for disabled.
+
+		For example::
+
+		  # echo 1 > /sys/bus/cdx/.../enable
+
+What:		/sys/bus/cdx/devices/.../reset
+Date:		March 2023
+Contact:	nipun.gupta@amd.com
+Description:
+		Writing y/1/on to this file resets the CDX device or all devices
+		on the bus. On resetting the device, the corresponding driver is
+		notified twice, once before the device is being reset, and again
+		after the reset has been complete.
+
+		For example::
+
+		  # echo 1 > /sys/bus/cdx/.../reset
+
+What:		/sys/bus/cdx/devices/.../remove
+Date:		March 2023
+Contact:	tarak.reddy@amd.com
+Description:
+		Writing y/1/on to this file removes the corresponding
+		device from the CDX bus. If the device is to be reconfigured
+		reconfigured in the Hardware, the device can be removed, so
+		that the device driver does not access the device while it is
+		being reconfigured.
+
+		For example::
+
+		  # echo 1 > /sys/bus/cdx/devices/.../remove
+
+What:		/sys/bus/cdx/devices/.../resource<N>
+Date:		July 2023
+Contact:	puneet.gupta@amd.com
+Description:
+		The resource binary file contains the content of the memory
+		regions. These files can be m'maped from userspace.
+
+What:		/sys/bus/cdx/devices/.../modalias
+Date:		July 2023
+Contact:	nipun.gupta@amd.com
+Description:
+		This attribute indicates the CDX ID of the device.
+		That is in the format:
+		cdx:vXXXXdXXXXsvXXXXsdXXXXcXXXXXX,
+		where:
+
+		    - vXXXX contains the vendor ID;
+		    - dXXXX contains the device ID;
+		    - svXXXX contains the subsystem vendor ID;
+		    - sdXXXX contains the subsystem device ID;
+		    - cXXXXXX contains the device class.