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, 226 insertions, 0 deletions

diff --git a/scripts/package/kernel.spec b/scripts/package/kernel.spec
new file mode 100644
index 000000000..46e80970f
--- /dev/null
+++ b/scripts/package/kernel.spec
@@ -0,0 +1,226 @@
+# _arch is undefined if /usr/lib/rpm/platform/*/macros was not included.
+%{!?_arch: %define _arch dummy}
+%{!?make: %define make make}
+%define makeflags %{?_smp_mflags} ARCH=%{ARCH}
+
+Name: kernel
+Summary: The Linux Kernel
+Version: %(echo %{KERNELRELEASE} | sed -e 's/-/_/g')
+Release: %{pkg_release}%{?dist}
+License: GPL
+Group: System Environment/Kernel
+Vendor: The Linux Community
+URL: https://www.kernel.org
+Source0: linux.tar.gz
+Source1: config
+Source2: diff.patch
+Provides: kernel-%{KERNELRELEASE}
+BuildRequires: bc binutils bison dwarves
+BuildRequires: (elfutils-devel or libdw-devel)
+BuildRequires: (elfutils-libelf-devel or libelf-devel) flex
+BuildRequires: gcc make openssl openssl-devel perl python3 rsync
+
+%description
+The Linux Kernel, the operating system core itself
+
+%package headers
+Summary: Header files for the Linux kernel for use by glibc
+Group: Development/System
+Obsoletes: kernel-headers < %{version}
+Provides: kernel-headers = %{version}
+%description headers
+Kernel-headers includes the C header files that specify the interface
+between the Linux kernel and userspace libraries and programs.  The
+header files define structures and constants that are needed for
+building most standard programs and are also needed for rebuilding the
+glibc package.
+
+%if %{with_devel}
+%package devel
+Summary: Development package for building kernel modules to match the %{version} kernel
+Group: System Environment/Kernel
+AutoReqProv: no
+%description -n kernel-devel
+This package provides kernel headers and makefiles sufficient to build modules
+against the %{version} kernel package.
+%endif
+
+%if %{with_debuginfo_manual}
+%package debuginfo
+Summary: Debug information package for the Linux kernel
+Group: Development/Debug
+AutoReq: 0
+AutoProv: 1
+%description debuginfo
+This package provides debug information for the kernel image and modules from the
+%{version} package.
+%define install_mod_strip 1
+%endif
+
+%if %{with_debuginfo_rpm}
+# list of debuginfo-related options taken from distribution kernel.spec
+# files
+%undefine _include_minidebuginfo
+%undefine _find_debuginfo_dwz_opts
+%undefine _unique_build_ids
+%undefine _unique_debug_names
+%undefine _unique_debug_srcs
+%undefine _debugsource_packages
+%undefine _debuginfo_subpackages
+
+# Preserve .BTF and .BTF.base sections in kernel modules during debuginfo
+# stripping. find-debuginfo.sh uses eu-strip which removes non-allocated ELF
+# sections like .BTF by default. .BTF.base is required for BTF distillation
+# support; without it, module BTF validation fails.
+%global with_keep_section %(%{__find_debuginfo} --help 2>&1 | grep -c keep-section)
+%if %{with_keep_section}
+%global _find_debuginfo_opts -r --keep-section .BTF --keep-section .BTF.base
+%else
+%global _find_debuginfo_opts -r
+%endif
+
+%global _missing_build_ids_terminate_build 1
+%global _no_recompute_build_ids 1
+%{debug_package}
+
+# later, we make all modules executable so that find-debuginfo.sh strips
+# them up. but they don't actually need to be executable, so remove the
+# executable bit, taking care to do it _after_ find-debuginfo.sh has run
+%define __spec_install_post \
+	%{?__debug_package:%{__debug_install_post}} \
+	%{__arch_install_post} \
+	%{__os_install_post} \
+	find %{buildroot}/lib/modules/%{KERNELRELEASE} -name "*.ko" -type f \\\
+		| xargs --no-run-if-empty chmod u-x
+%else
+%define __spec_install_post /usr/lib/rpm/brp-compress || :
+%endif
+# some (but not all) versions of rpmbuild emit %%debug_package with
+# %%install. since we've already emitted it manually, that would cause
+# a package redefinition error. ensure that doesn't happen
+%define debug_package %{nil}
+
+%prep
+%setup -q -n linux
+cp %{SOURCE1} .config
+patch -p1 < %{SOURCE2}
+
+%build
+%{make} %{makeflags} KERNELRELEASE=%{KERNELRELEASE} KBUILD_BUILD_VERSION=%{release}
+
+%install
+mkdir -p %{buildroot}/lib/modules/%{KERNELRELEASE}
+cp $(%{make} %{makeflags} -s image_name) %{buildroot}/lib/modules/%{KERNELRELEASE}/vmlinuz
+# DEPMOD=true makes depmod no-op. We do not package depmod-generated files.
+%{make} %{makeflags} INSTALL_MOD_PATH=%{buildroot} %{?install_mod_strip:INSTALL_MOD_STRIP=1} DEPMOD=true modules_install
+%{make} %{makeflags} INSTALL_HDR_PATH=%{buildroot}/usr headers_install
+cp System.map %{buildroot}/lib/modules/%{KERNELRELEASE}
+cp .config %{buildroot}/lib/modules/%{KERNELRELEASE}/config
+if %{make} %{makeflags} run-command KBUILD_RUN_COMMAND='test -d ${srctree}/arch/${SRCARCH}/boot/dts' 2>/dev/null; then
+	%{make} %{makeflags} INSTALL_DTBS_PATH=%{buildroot}/lib/modules/%{KERNELRELEASE}/dtb dtbs_install
+fi
+ln -fns /usr/src/kernels/%{KERNELRELEASE} %{buildroot}/lib/modules/%{KERNELRELEASE}/build
+%if %{with_devel}
+%{make} %{makeflags} run-command KBUILD_RUN_COMMAND='${srctree}/scripts/package/install-extmod-build %{buildroot}/usr/src/kernels/%{KERNELRELEASE}'
+%endif
+
+{
+	echo "/lib/modules/%{KERNELRELEASE}"
+
+	for x in alias alias.bin builtin.alias.bin builtin.bin dep dep.bin \
+				devname softdep symbols symbols.bin weakdep; do
+		echo "%ghost /lib/modules/%{KERNELRELEASE}/modules.${x}"
+	done
+
+	for x in System.map config vmlinuz; do
+		echo "%ghost /boot/${x}-%{KERNELRELEASE}"
+	done
+
+	if [ -d "%{buildroot}/lib/modules/%{KERNELRELEASE}/dtb" ];then
+		find "%{buildroot}/lib/modules/%{KERNELRELEASE}/dtb" -printf "%%%ghost /boot/dtb-%{KERNELRELEASE}/%%P\n"
+	fi
+
+	echo "%exclude /lib/modules/%{KERNELRELEASE}/build"
+} > %{buildroot}/kernel.list
+
+%if 0%{with_debuginfo_manual}%{with_debuginfo_rpm} > 0
+# copying vmlinux directly to the debug directory means it will not get
+# stripped (but its source paths will still be collected + fixed up)
+mkdir -p %{buildroot}/usr/lib/debug/lib/modules/%{KERNELRELEASE}
+cp vmlinux %{buildroot}/usr/lib/debug/lib/modules/%{KERNELRELEASE}
+%endif
+
+%if %{with_debuginfo_rpm}
+# make modules executable so that find-debuginfo.sh strips them. this
+# will be undone later in %%__spec_install_post
+find %{buildroot}/lib/modules/%{KERNELRELEASE} -name "*.ko" -type f \
+	| xargs --no-run-if-empty chmod u+x
+%endif
+
+%if %{with_debuginfo_manual}
+echo /usr/lib/debug/lib/modules/%{KERNELRELEASE}/vmlinux > %{buildroot}/debuginfo.list
+while read -r mod; do
+	mod="${mod%.o}.ko"
+	dbg="%{buildroot}/usr/lib/debug/lib/modules/%{KERNELRELEASE}/kernel/${mod}"
+	buildid=$("${READELF:-readelf}" -n "${mod}" | sed -n 's@^.*Build ID: \(..\)\(.*\)@\1/\2@p')
+	link="%{buildroot}/usr/lib/debug/.build-id/${buildid}.debug"
+
+	mkdir -p "${dbg%/*}" "${link%/*}"
+	"${OBJCOPY:-objcopy}" --only-keep-debug "${mod}" "${dbg}"
+	ln -sf --relative "${dbg}" "${link}"
+
+	echo "${dbg#%{buildroot}}" >> %{buildroot}/debuginfo.list
+	echo "${link#%{buildroot}}" >> %{buildroot}/debuginfo.list
+done < modules.order
+%endif
+
+%clean
+rm -rf %{buildroot}
+%if %{with_debuginfo_rpm}
+rm -f debugfiles.list debuglinks.list debugsourcefiles.list debugsources.list \
+	elfbins.list
+%endif
+
+%post
+if [ -x /usr/bin/kernel-install ]; then
+	/usr/bin/kernel-install add %{KERNELRELEASE} /lib/modules/%{KERNELRELEASE}/vmlinuz
+fi
+for file in vmlinuz System.map config; do
+	if ! cmp --silent "/lib/modules/%{KERNELRELEASE}/${file}" "/boot/${file}-%{KERNELRELEASE}"; then
+		cp "/lib/modules/%{KERNELRELEASE}/${file}" "/boot/${file}-%{KERNELRELEASE}"
+	fi
+done
+if [ -d "/lib/modules/%{KERNELRELEASE}/dtb" ] && \
+   ! diff -rq "/lib/modules/%{KERNELRELEASE}/dtb" "/boot/dtb-%{KERNELRELEASE}" >/dev/null 2>&1; then
+	rm -rf "/boot/dtb-%{KERNELRELEASE}"
+	cp -r "/lib/modules/%{KERNELRELEASE}/dtb" "/boot/dtb-%{KERNELRELEASE}"
+fi
+if [ ! -e "/lib/modules/%{KERNELRELEASE}/modules.dep" ]; then
+	/usr/sbin/depmod %{KERNELRELEASE}
+fi
+
+%preun
+if [ -x /usr/bin/kernel-install ]; then
+kernel-install remove %{KERNELRELEASE}
+fi
+
+%files -f %{buildroot}/kernel.list
+%defattr (-, root, root)
+%exclude /kernel.list
+
+%files headers
+%defattr (-, root, root)
+/usr/include
+
+%if %{with_devel}
+%files devel
+%defattr (-, root, root)
+/usr/src/kernels/%{KERNELRELEASE}
+/lib/modules/%{KERNELRELEASE}/build
+%endif
+
+%if %{with_debuginfo_manual}
+%files -f %{buildroot}/debuginfo.list debuginfo
+%defattr (-, root, root)
+%exclude /debuginfo.list
+%endif