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, 37 insertions, 0 deletions

diff --git a/net/atm/Kconfig b/net/atm/Kconfig
new file mode 100644
index 000000000..dfdc3a855
--- /dev/null
+++ b/net/atm/Kconfig
@@ -0,0 +1,37 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Asynchronous Transfer Mode (ATM)
+#
+
+config ATM
+	tristate "Asynchronous Transfer Mode (ATM)"
+	help
+	  ATM is a high-speed networking technology for Local Area Networks
+	  and Wide Area Networks.  It uses a fixed packet size and is
+	  connection oriented, allowing for the negotiation of minimum
+	  bandwidth requirements.
+
+	  In order to participate in an ATM network, your Linux box needs an
+	  ATM networking card. If you have that, say Y here and to the driver
+	  of your ATM card below.
+
+	  Note that you need a set of user-space programs to actually make use
+	  of ATM.  See the file <file:Documentation/networking/atm.rst> for
+	  further details.
+
+config ATM_BR2684
+	tristate "RFC1483/2684 Bridged protocols"
+	depends on ATM && INET
+	help
+	  ATM PVCs can carry ethernet PDUs according to RFC2684 (formerly 1483)
+	  This device will act like an ethernet from the kernels point of view,
+	  with the traffic being carried by ATM PVCs (currently 1 PVC/device).
+	  This is sometimes used over DSL lines.  If in doubt, say N.
+
+config ATM_BR2684_IPFILTER
+	bool "Per-VC IP filter kludge"
+	depends on ATM_BR2684
+	help
+	  This is an experimental mechanism for users who need to terminate a
+	  large number of IP-only vcc's.  Do not enable this unless you are sure
+	  you know what you are doing.