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, 119 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-block-device b/Documentation/ABI/testing/sysfs-block-device
new file mode 100644
index 000000000..2d543cfa4
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-block-device
@@ -0,0 +1,119 @@
+What:		/sys/block/*/device/sw_activity
+Date:		Jun, 2008
+KernelVersion:	v2.6.27
+Contact:	linux-ide@vger.kernel.org
+Description:
+		(RW) Used by drivers which support software controlled activity
+		LEDs.
+
+		It has the following valid values:
+
+		==	========================================================
+		0	OFF - the LED is not activated on activity
+		1	BLINK_ON - the LED blinks on every 10ms when activity is
+			detected.
+		2	BLINK_OFF - the LED is on when idle, and blinks off
+			every 10ms when activity is detected.
+		==	========================================================
+
+		Note that the user must turn sw_activity OFF it they wish to
+		control the activity LED via the em_message file.
+
+
+What:		/sys/block/*/device/unload_heads
+Date:		Sep, 2008
+KernelVersion:	v2.6.28
+Contact:	linux-ide@vger.kernel.org
+Description:
+		(RW) Hard disk shock protection
+
+		Writing an integer value to this file will take the heads of the
+		respective drive off the platter and block all I/O operations
+		for the specified number of milliseconds.
+
+		- If the device does not support the unload heads feature,
+		  access is denied with -EOPNOTSUPP.
+		- The maximal value accepted for a timeout is 30000
+		  milliseconds.
+		- A previously set timeout can be cancelled and disk can resume
+		  normal operation immediately by specifying a timeout of 0.
+		- Some hard drives only comply with an earlier version of the
+		  ATA standard, but support the unload feature nonetheless.
+		  There is no safe way Linux can detect these devices, so this
+		  is not enabled by default. If it is known that your device
+		  does support the unload feature, then you can tell the kernel
+		  to enable it by writing -1. It can be disabled again by
+		  writing -2.
+		- Values below -2 are rejected with -EINVAL
+
+		For more information, see
+		Documentation/admin-guide/laptops/disk-shock-protection.rst
+
+
+What:		/sys/block/*/device/ncq_prio_enable
+Date:		Oct, 2016
+KernelVersion:	v4.10
+Contact:	linux-ide@vger.kernel.org
+Description:
+		(RW) Write to the file to turn on or off the SATA NCQ (native
+		command queueing) priority support. By default this feature is
+		turned off. If the device does not support the SATA NCQ
+		priority feature, writing "1" to this file results in an error
+		(see ncq_prio_supported).
+
+
+What:		/sys/block/*/device/sas_ncq_prio_enable
+Date:		Oct, 2016
+KernelVersion:	v4.10
+Contact:	linux-ide@vger.kernel.org
+Description:
+		(RW) This is the equivalent of the ncq_prio_enable attribute
+		file for SATA devices connected to a SAS host-bus-adapter
+		(HBA) implementing support for the SATA NCQ priority feature.
+		This file does not exist if the HBA driver does not implement
+		support for the SATA NCQ priority feature, regardless of the
+		device support for this feature (see sas_ncq_prio_supported).
+
+
+What:		/sys/block/*/device/ncq_prio_supported
+Date:		Aug, 2021
+KernelVersion:	v5.15
+Contact:	linux-ide@vger.kernel.org
+Description:
+		(RO) Indicates if the device supports the SATA NCQ (native
+		command queueing) priority feature.
+
+
+What:		/sys/block/*/device/sas_ncq_prio_supported
+Date:		Aug, 2021
+KernelVersion:	v5.15
+Contact:	linux-ide@vger.kernel.org
+Description:
+		(RO) This is the equivalent of the ncq_prio_supported attribute
+		file for SATA devices connected to a SAS host-bus-adapter
+		(HBA) implementing support for the SATA NCQ priority feature.
+		This file does not exist if the HBA driver does not implement
+		support for the SATA NCQ priority feature, regardless of the
+		device support for this feature.
+
+
+What:		/sys/block/*/device/cdl_supported
+Date:		May, 2023
+KernelVersion:	v6.5
+Contact:	linux-scsi@vger.kernel.org
+Description:
+		(RO) Indicates if the device supports the command duration
+		limits feature found in some ATA and SCSI devices.
+
+
+What:		/sys/block/*/device/cdl_enable
+Date:		May, 2023
+KernelVersion:	v6.5
+Contact:	linux-scsi@vger.kernel.org
+Description:
+		(RW) For a device supporting the command duration limits
+		feature, write to the file to turn on or off the feature.
+		By default this feature is turned off.
+		Writing "1" to this file enables the use of command duration
+		limits for read and write commands in the kernel and turns on
+		the feature on the device. Writing "0" disables the feature.