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, 27 insertions, 0 deletions

diff --git a/drivers/misc/pvpanic/Kconfig b/drivers/misc/pvpanic/Kconfig
new file mode 100644
index 000000000..12d40a21f
--- /dev/null
+++ b/drivers/misc/pvpanic/Kconfig
@@ -0,0 +1,27 @@
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Pvpanic Kconfig
+#
+# Copyright (C) 2021 Oracle.
+#
+
+config PVPANIC
+	bool "pvpanic device support"
+	help
+	  This option allows to select a specific pvpanic device driver.
+	  pvpanic is a paravirtualized device provided by QEMU; it lets
+	  a virtual machine (guest) communicate panic events to the host.
+
+config PVPANIC_MMIO
+	tristate "pvpanic MMIO device support"
+	depends on HAS_IOMEM && (ACPI || OF) && PVPANIC
+	help
+	  This driver provides support for the MMIO pvpanic device.
+
+config PVPANIC_PCI
+	tristate "pvpanic PCI device support"
+	depends on PCI && PVPANIC
+	help
+	  This driver provides support for the PCI pvpanic device.
+	  pvpanic is a paravirtualized device provided by QEMU which
+	  forwards the panic events from the guest to the host.