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, 69 insertions, 0 deletions

diff --git a/scripts/Makefile b/scripts/Makefile
new file mode 100644
index 000000000..3434a82a1
--- /dev/null
+++ b/scripts/Makefile
@@ -0,0 +1,69 @@
+# SPDX-License-Identifier: GPL-2.0
+###
+# scripts contains sources for various helper programs used throughout
+# the kernel for the build process.
+
+hostprogs-always-$(CONFIG_KALLSYMS)			+= kallsyms
+hostprogs-always-$(BUILD_C_RECORDMCOUNT)		+= recordmcount
+hostprogs-always-$(CONFIG_BUILDTIME_TABLE_SORT)		+= sorttable
+hostprogs-always-$(CONFIG_ASN1)				+= asn1_compiler
+hostprogs-always-$(CONFIG_MODULE_SIG_FORMAT)		+= sign-file
+hostprogs-always-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE)	+= insert-sys-cert
+hostprogs-always-$(CONFIG_RUST_KERNEL_DOCTESTS)		+= rustdoc_test_builder
+hostprogs-always-$(CONFIG_RUST_KERNEL_DOCTESTS)		+= rustdoc_test_gen
+hostprogs-always-$(CONFIG_TRACEPOINTS)			+= tracepoint-update
+
+sorttable-objs := sorttable.o elf-parse.o
+tracepoint-update-objs := tracepoint-update.o elf-parse.o
+
+ifneq ($(or $(CONFIG_X86_64),$(CONFIG_X86_32)),)
+always-$(CONFIG_RUST)					+= target.json
+filechk_rust_target = $< < include/config/auto.conf
+
+$(obj)/target.json: scripts/generate_rust_target include/config/auto.conf FORCE
+	$(call filechk,rust_target)
+endif
+
+hostprogs += generate_rust_target
+generate_rust_target-rust := y
+rustdoc_test_builder-rust := y
+rustdoc_test_gen-rust := y
+
+HOSTCFLAGS_tracepoint-update.o = -I$(srctree)/tools/include
+HOSTCFLAGS_elf-parse.o = -I$(srctree)/tools/include
+HOSTCFLAGS_sorttable.o = -I$(srctree)/tools/include
+HOSTLDLIBS_sorttable = -lpthread
+HOSTCFLAGS_asn1_compiler.o = -I$(srctree)/include
+HOSTCFLAGS_sign-file.o = $(shell $(HOSTPKG_CONFIG) --cflags libcrypto 2> /dev/null)
+HOSTCFLAGS_sign-file.o += -I$(srctree)/tools/include/uapi/
+HOSTLDLIBS_sign-file = $(shell $(HOSTPKG_CONFIG) --libs libcrypto 2> /dev/null || echo -lcrypto)
+
+ifdef CONFIG_UNWINDER_ORC
+ifeq ($(ARCH),x86_64)
+SRCARCH := x86
+endif
+ifeq ($(ARCH),loongarch)
+SRCARCH := loongarch
+endif
+HOSTCFLAGS_sorttable.o += -I$(srctree)/tools/arch/$(SRCARCH)/include
+HOSTCFLAGS_sorttable.o += -DUNWINDER_ORC_ENABLED
+endif
+
+ifdef CONFIG_BUILDTIME_MCOUNT_SORT
+HOSTCFLAGS_sorttable.o += -DMCOUNT_SORT_ENABLED
+endif
+
+# The following programs are only built on demand
+hostprogs += unifdef gen_packed_field_checks
+
+# The module linker script is preprocessed on demand
+targets += module.lds
+
+subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
+subdir-$(CONFIG_GENKSYMS) += genksyms
+subdir-$(CONFIG_GENDWARFKSYMS) += gendwarfksyms
+subdir-$(CONFIG_SECURITY_SELINUX) += selinux
+subdir-$(CONFIG_SECURITY_IPE) += ipe
+
+# Let clean descend into subdirs
+subdir-	+= basic dtc gdb kconfig mod