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, 43 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/procfs-diskstats b/Documentation/ABI/testing/procfs-diskstats
new file mode 100644
index 000000000..6a719cf20
--- /dev/null
+++ b/Documentation/ABI/testing/procfs-diskstats
@@ -0,0 +1,43 @@
+What:		/proc/diskstats
+Date:		February 2008
+Contact:	Jerome Marchand <jmarchan@redhat.com>
+Description:
+		The /proc/diskstats file displays the I/O statistics
+		of block devices. Each line contains the following 14
+		fields:
+
+		==  ===================================
+		 1  major number
+		 2  minor number
+		 3  device name
+		 4  reads completed successfully
+		 5  reads merged
+		 6  sectors read
+		 7  time spent reading (ms)
+		 8  writes completed
+		 9  writes merged
+		10  sectors written
+		11  time spent writing (ms)
+		12  I/Os currently in progress
+		13  time spent doing I/Os (ms)
+		14  weighted time spent doing I/Os (ms)
+		==  ===================================
+
+		Kernel 4.18+ appends four more fields for discard
+		tracking putting the total at 18:
+
+		==  ===================================
+		15  discards completed successfully
+		16  discards merged
+		17  sectors discarded
+		18  time spent discarding
+		==  ===================================
+
+		Kernel 5.5+ appends two more fields for flush requests:
+
+		==  =====================================
+		19  flush requests completed successfully
+		20  time spent flushing
+		==  =====================================
+
+		For more details refer to Documentation/admin-guide/iostats.rst