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, 71 insertions, 0 deletions

diff --git a/arch/microblaze/Kconfig.platform b/arch/microblaze/Kconfig.platform
new file mode 100644
index 000000000..9cf9007ed
--- /dev/null
+++ b/arch/microblaze/Kconfig.platform
@@ -0,0 +1,71 @@
+# SPDX-License-Identifier: GPL-2.0-only
+# For a description of the syntax of this configuration file,
+# see Documentation/kbuild/kconfig-language.rst.
+#
+# Platform selection Kconfig menu for MicroBlaze targets
+#
+
+menu "Platform options"
+
+config OPT_LIB_FUNCTION
+	bool "Optimized lib function"
+	default y
+	help
+	  Turns on optimized library functions (memcpy and memmove).
+	  They are optimized by using word alignment. This will work
+	  fine if both source and destination are aligned on the same
+	  boundary. However, if they are aligned on different boundaries
+	  shifts will be necessary. This might result in bad performance
+	  on MicroBlaze systems without a barrel shifter.
+
+config OPT_LIB_ASM
+	bool "Optimized lib function ASM"
+	depends on OPT_LIB_FUNCTION && (XILINX_MICROBLAZE0_USE_BARREL = 1)
+	depends on CPU_BIG_ENDIAN
+	default n
+	help
+	  Turns on optimized library functions (memcpy and memmove).
+	  They are written in assembly.
+
+# Definitions for MICROBLAZE0
+comment "Definitions for MICROBLAZE0"
+
+config KERNEL_BASE_ADDR
+	hex "Physical address where Linux Kernel is"
+	default "0x90000000"
+	help
+	  BASE Address for kernel
+
+config XILINX_MICROBLAZE0_FAMILY
+	string "Targeted FPGA family"
+	default "virtex5"
+
+config XILINX_MICROBLAZE0_USE_MSR_INSTR
+	int "USE_MSR_INSTR range (0:1)"
+	default 0
+
+config XILINX_MICROBLAZE0_USE_PCMP_INSTR
+	int "USE_PCMP_INSTR range (0:1)"
+	default 0
+
+config XILINX_MICROBLAZE0_USE_BARREL
+	int "USE_BARREL range (0:1)"
+	default 0
+
+config XILINX_MICROBLAZE0_USE_DIV
+	int "USE_DIV range (0:1)"
+	default 0
+
+config XILINX_MICROBLAZE0_USE_HW_MUL
+	int "USE_HW_MUL values (0=NONE, 1=MUL32, 2=MUL64)"
+	default 0
+
+config XILINX_MICROBLAZE0_USE_FPU
+	int "USE_FPU values (0=NONE, 1=BASIC, 2=EXTENDED)"
+	default 0
+
+config XILINX_MICROBLAZE0_HW_VER
+	string "Core version number"
+	default "7.10.d"
+
+endmenu