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, 61 insertions, 0 deletions

diff --git a/Documentation/admin-guide/device-mapper/striped.rst b/Documentation/admin-guide/device-mapper/striped.rst
new file mode 100644
index 000000000..e9a8da192
--- /dev/null
+++ b/Documentation/admin-guide/device-mapper/striped.rst
@@ -0,0 +1,61 @@
+=========
+dm-stripe
+=========
+
+Device-Mapper's "striped" target is used to create a striped (i.e. RAID-0)
+device across one or more underlying devices. Data is written in "chunks",
+with consecutive chunks rotating among the underlying devices. This can
+potentially provide improved I/O throughput by utilizing several physical
+devices in parallel.
+
+Parameters: <num devs> <chunk size> [<dev path> <offset>]+
+    <num devs>:
+	Number of underlying devices.
+    <chunk size>:
+	Size of each chunk of data. Must be at least as
+        large as the system's PAGE_SIZE.
+    <dev path>:
+	Full pathname to the underlying block-device, or a
+	"major:minor" device-number.
+    <offset>:
+	Starting sector within the device.
+
+One or more underlying devices can be specified. The striped device size must
+be a multiple of the chunk size multiplied by the number of underlying devices.
+
+
+Example scripts
+===============
+
+::
+
+  #!/usr/bin/perl -w
+  # Create a striped device across any number of underlying devices. The device
+  # will be called "stripe_dev" and have a chunk-size of 128k.
+
+  my $chunk_size = 128 * 2;
+  my $dev_name = "stripe_dev";
+  my $num_devs = @ARGV;
+  my @devs = @ARGV;
+  my ($min_dev_size, $stripe_dev_size, $i);
+
+  if (!$num_devs) {
+          die("Specify at least one device\n");
+  }
+
+  $min_dev_size = `blockdev --getsz $devs[0]`;
+  for ($i = 1; $i < $num_devs; $i++) {
+          my $this_size = `blockdev --getsz $devs[$i]`;
+          $min_dev_size = ($min_dev_size < $this_size) ?
+                          $min_dev_size : $this_size;
+  }
+
+  $stripe_dev_size = $min_dev_size * $num_devs;
+  $stripe_dev_size -= $stripe_dev_size % ($chunk_size * $num_devs);
+
+  $table = "0 $stripe_dev_size striped $num_devs $chunk_size";
+  for ($i = 0; $i < $num_devs; $i++) {
+          $table .= " $devs[$i] 0";
+  }
+
+  `echo $table | dmsetup create $dev_name`;