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, 47 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-block-dm b/Documentation/ABI/testing/sysfs-block-dm
new file mode 100644
index 000000000..f9f2339b9
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-block-dm
@@ -0,0 +1,47 @@
+What:		/sys/block/dm-<num>/dm/name
+Date:		January 2009
+KernelVersion:	2.6.29
+Contact:	dm-devel@redhat.com
+Description:	Device-mapper device name.
+		Read-only string containing mapped device name.
+Users:		util-linux, device-mapper udev rules
+
+What:		/sys/block/dm-<num>/dm/uuid
+Date:		January 2009
+KernelVersion:	2.6.29
+Contact:	dm-devel@redhat.com
+Description:	Device-mapper device UUID.
+		Read-only string containing DM-UUID or empty string
+		if DM-UUID is not set.
+Users:		util-linux, device-mapper udev rules
+
+What:		/sys/block/dm-<num>/dm/suspended
+Date:		June 2009
+KernelVersion:	2.6.31
+Contact:	dm-devel@redhat.com
+Description:	Device-mapper device suspend state.
+		Contains the value 1 while the device is suspended.
+		Otherwise it contains 0. Read-only attribute.
+Users:		util-linux, device-mapper udev rules
+
+What:		/sys/block/dm-<num>/dm/rq_based_seq_io_merge_deadline
+Date:		March 2015
+KernelVersion:	4.1
+Contact:	dm-devel@redhat.com
+Description:	Allow control over how long a request that is a
+		reasonable merge candidate can be queued on the request
+		queue.  The resolution of this deadline is in
+		microseconds (ranging from 1 to 100000 usecs).
+		Setting this attribute to 0 (the default) will disable
+		request-based DM's merge heuristic and associated extra
+		accounting.  This attribute is not applicable to
+		bio-based DM devices so it will only ever report 0 for
+		them.
+
+What:		/sys/block/dm-<num>/dm/use_blk_mq
+Date:		March 2015
+KernelVersion:	4.1
+Contact:	dm-devel@redhat.com
+Description:	Request-based Device-mapper blk-mq I/O path mode.
+		Contains the value 1 if the device is using blk-mq.
+		Otherwise it contains 0. Read-only attribute.