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, 59 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-rapidio b/Documentation/ABI/testing/sysfs-class-rapidio
new file mode 100644
index 000000000..81e091455
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-rapidio
@@ -0,0 +1,59 @@
+What:		/sys/class/rapidio_port
+Description:
+		On-chip RapidIO controllers and PCIe-to-RapidIO bridges
+		(referenced as "Master Port" or "mport") are presented in sysfs
+		as the special class of devices: "rapidio_port".
+		The /sys/class/rapidio_port subdirectory contains individual
+		subdirectories named as "rapidioN" where N = mport ID registered
+		with RapidIO subsystem.
+
+		NOTE: An mport ID is not a RapidIO destination ID assigned to a
+		given local mport device.
+
+What:		/sys/class/rapidio_port/rapidio<N>/sys_size
+Date:		Apr, 2014
+KernelVersion:	v3.15
+Contact:	Matt Porter <mporter@kernel.crashing.org>,
+		Alexandre Bounine <alexandre.bounine@idt.com>
+Description:
+		(RO) reports RapidIO common transport system size:
+
+		0 = small (8-bit destination ID, max. 256 devices),
+
+		1 = large (16-bit destination ID, max. 65536 devices).
+
+What:		/sys/class/rapidio_port/rapidio<N>/port_destid
+Date:		Apr, 2014
+KernelVersion:	v3.15
+Contact:	Matt Porter <mporter@kernel.crashing.org>,
+		Alexandre Bounine <alexandre.bounine@idt.com>
+Description:
+
+(RO) reports RapidIO destination ID assigned to the given
+RapidIO mport device. If value 0xFFFFFFFF is returned this means
+that no valid destination ID have been assigned to the mport
+(yet). Normally, before enumeration/discovery have been executed
+only fabric enumerating mports have a valid destination ID
+assigned to them using "hdid=..." rapidio module parameter.
+
+After enumeration or discovery was performed for a given mport device,
+the corresponding subdirectory will also contain subdirectories for each
+child RapidIO device connected to the mport.
+
+The example below shows mport device subdirectory with several child RapidIO
+devices attached to it::
+
+    [rio@rapidio ~]$ ls /sys/class/rapidio_port/rapidio0/ -l
+    total 0
+    drwxr-xr-x 3 root root    0 Feb 11 15:10 00:e:0001
+    drwxr-xr-x 3 root root    0 Feb 11 15:10 00:e:0004
+    drwxr-xr-x 3 root root    0 Feb 11 15:10 00:e:0007
+    drwxr-xr-x 3 root root    0 Feb 11 15:10 00:s:0002
+    drwxr-xr-x 3 root root    0 Feb 11 15:10 00:s:0003
+    drwxr-xr-x 3 root root    0 Feb 11 15:10 00:s:0005
+    lrwxrwxrwx 1 root root    0 Feb 11 15:11 device -> ../../../0000:01:00.0
+    -r--r--r-- 1 root root 4096 Feb 11 15:11 port_destid
+    drwxr-xr-x 2 root root    0 Feb 11 15:11 power
+    lrwxrwxrwx 1 root root    0 Feb 11 15:04 subsystem -> ../../../../../../class/rapidio_port
+    -r--r--r-- 1 root root 4096 Feb 11 15:11 sys_size
+    -rw-r--r-- 1 root root 4096 Feb 11 15:04 uevent