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, 118 insertions, 0 deletions

diff --git a/fs/btrfs/Kconfig b/fs/btrfs/Kconfig
new file mode 100644
index 000000000..4b10d78ed
--- /dev/null
+++ b/fs/btrfs/Kconfig
@@ -0,0 +1,118 @@
+# SPDX-License-Identifier: GPL-2.0
+
+config BTRFS_FS
+	tristate "Btrfs filesystem support"
+	select BLK_CGROUP_PUNT_BIO
+	select CRC32
+	select CRYPTO_LIB_BLAKE2B
+	select CRYPTO_LIB_SHA256
+	select ZLIB_INFLATE
+	select ZLIB_DEFLATE
+	select LZO_COMPRESS
+	select LZO_DECOMPRESS
+	select ZSTD_COMPRESS
+	select ZSTD_DECOMPRESS
+	select FS_IOMAP
+	select RAID6_PQ
+	select XOR_BLOCKS
+	select XXHASH
+	depends on PAGE_SIZE_LESS_THAN_256KB
+
+	help
+	  Btrfs is a general purpose copy-on-write filesystem with extents,
+	  writable snapshotting, support for multiple devices and many more
+	  features focused on fault tolerance, repair and easy administration.
+
+	  The filesystem disk format is no longer unstable, and it's not
+	  expected to change unless there are strong reasons to do so. If there
+	  is a format change, file systems with a unchanged format will
+	  continue to be mountable and usable by newer kernels.
+
+	  For more information, please see the web pages at
+	  https://btrfs.readthedocs.io
+
+	  To compile this file system support as a module, choose M here. The
+	  module will be called btrfs.
+
+	  If unsure, say N.
+
+config BTRFS_FS_POSIX_ACL
+	bool "Btrfs POSIX Access Control Lists"
+	depends on BTRFS_FS
+	select FS_POSIX_ACL
+	help
+	  POSIX Access Control Lists (ACLs) support permissions for users and
+	  groups beyond the owner/group/world scheme.
+
+	  If you don't know what Access Control Lists are, say N
+
+config BTRFS_FS_RUN_SANITY_TESTS
+	bool "Btrfs will run sanity tests upon loading"
+	depends on BTRFS_FS
+	help
+	  This will run sanity tests for core functionality like free space,
+	  extent maps, extent io, extent buffers, inodes, qgroups and others,
+	  at module load time.  These are mostly regression tests and are only
+	  interesting to developers.
+
+	  If unsure, say N.
+
+config BTRFS_DEBUG
+	bool "Btrfs debugging support"
+	depends on BTRFS_FS
+	select REF_TRACKER if STACKTRACE_SUPPORT
+	help
+	  Enable run-time debugging support for the btrfs filesystem.
+
+	  Additional potentially expensive checks, debugging functionality or
+	  sysfs exported information is enabled, like leak checks of internal
+	  objects, optional forced space fragmentation and /sys/fs/btrfs/debug .
+	  This has negative impact on performance.
+
+	  If unsure, say N.
+
+config BTRFS_ASSERT
+	bool "Btrfs assert support"
+	depends on BTRFS_FS
+	help
+	  Enable run-time assertion checking. Additional safety checks are
+	  done, simple enough not to affect performance but verify invariants
+	  and assumptions of code to run properly. This may result in panics,
+	  and is meant for developers but can be enabled in general.
+
+	  If unsure, say N.
+
+config BTRFS_EXPERIMENTAL
+	bool "Btrfs experimental features"
+	depends on BTRFS_FS
+	default n
+	help
+	  Enable experimental features.  These features may not be stable enough
+	  for end users.  This is meant for btrfs developers or users who wish
+	  to test the functionality and report problems.
+
+	  Current list:
+
+	  - RAID mirror read policy - additional read policies for balancing
+				      reading from redundant block group
+				      profiles (currently: pid, round-robin,
+				      fixed devid)
+
+	  - send stream protocol v3 - fs-verity support
+
+	  - raid-stripe-tree - additional mapping of extents to devices to
+			       support RAID1* profiles on zoned devices,
+			       RAID56 not yet supported
+
+	  - extent tree v2 - complex rework of extent tracking
+
+	  - block size > page size support - needs transparent huge page and
+					     non-HIGHMEM system
+
+	  - huge folios for data - folios can be as large as 2MiB now
+
+	  - asynchronous checksum generation for data writes
+
+	  - remap-tree - logical address remapping tree
+
+	  If unsure, say N.