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f1d87664b8
A long standing issue in the upstream kernel packaging is that the
linux-headers package is not cross-compiled.
For example, you can cross-build Debian packages for arm64 by running
the following command:
$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- bindeb-pkg
However, the generated linux-headers-*_arm64.deb is useless because the
host programs in it were built for your build machine architecture
(likely x86), not arm64.
The Debian kernel maintains its own Makefiles to cross-compile host
tools without relying on Kbuild. [1]
Instead of adding such full custom Makefiles, this commit adds a small
piece of code to cross-compile host programs located under the scripts/
directory.
A straightforward solution is to pass HOSTCC=${CROSS_COMPILE}gcc, but it
would also cross-compile scripts/basic/fixdep, which needs to be native
to process the if_changed_dep macro. (This approach may work under some
circumstances; you can execute foreign architecture programs with the
help of binfmt_misc because Debian systems enable CONFIG_BINFMT_MISC,
but it would require installing QEMU and libc for that architecture.)
A trick is to use the external module build (KBUILD_EXTMOD=), which
does not rebuild scripts/basic/fixdep. ${CC} needs to be able to link
userspace programs (CONFIG_CC_CAN_LINK=y).
There are known limitations:
- GCC plugins
It would possible to rebuild GCC plugins for the target architecture
by passing HOSTCXX=${CROSS_COMPILE}g++ with necessary packages
installed, but gcc on the installed system emits
"cc1: error: incompatible gcc/plugin versions".
- objtool and resolve_btfids
These are built by the tools build system. They are not covered by
the current solution. The resulting linux-headers package is broken
if CONFIG_OBJTOOL or CONFIG_DEBUG_INFO_BTF is enabled.
I only tested this with Debian, but it should work for other package
systems as well.
[1]: https://salsa.debian.org/kernel-team/linux/-/blob/debian/6.9.9-1/debian/rules.real#L586
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
81 lines
2.4 KiB
Bash
Executable file
81 lines
2.4 KiB
Bash
Executable file
#!/bin/sh
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# SPDX-License-Identifier: GPL-2.0-only
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set -eu
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destdir=${1}
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is_enabled() {
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grep -q "^$1=y" include/config/auto.conf
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}
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find_in_scripts() {
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find scripts \
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\( -name atomic -o -name dtc -o -name kconfig -o -name package \) -prune -o \
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! -name unifdef -a ! -name mk_elfconfig -a \( -type f -o -type l \) -print
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}
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mkdir -p "${destdir}"
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(
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cd "${srctree}"
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echo Makefile
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find "arch/${SRCARCH}" -maxdepth 1 -name 'Makefile*'
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find "arch/${SRCARCH}" -name generated -prune -o -name include -type d -print
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find "arch/${SRCARCH}" -name Kbuild.platforms -o -name Platform
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find include \( -name config -o -name generated \) -prune -o \( -type f -o -type l \) -print
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find_in_scripts
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) | tar -c -f - -C "${srctree}" -T - | tar -xf - -C "${destdir}"
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{
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if is_enabled CONFIG_OBJTOOL; then
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echo tools/objtool/objtool
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fi
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echo Module.symvers
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echo "arch/${SRCARCH}/include/generated"
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echo include/config/auto.conf
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echo include/config/kernel.release
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echo include/generated
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find_in_scripts
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if is_enabled CONFIG_GCC_PLUGINS; then
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find scripts/gcc-plugins -name '*.so'
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fi
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} | tar -c -f - -T - | tar -xf - -C "${destdir}"
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# When ${CC} and ${HOSTCC} differ, we are likely cross-compiling. Rebuild host
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# programs using ${CC}. This assumes CC=${CROSS_COMPILE}gcc, which is usually
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# the case for package building. It does not cross-compile when CC=clang.
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#
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# This caters to host programs that participate in Kbuild. objtool and
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# resolve_btfids are out of scope.
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if [ "${CC}" != "${HOSTCC}" ] && is_enabled CONFIG_CC_CAN_LINK; then
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echo "Rebuilding host programs with ${CC}..."
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cat <<-'EOF' > "${destdir}/Kbuild"
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subdir-y := scripts
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EOF
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# HOSTCXX is not overridden. The C++ compiler is used to build:
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# - scripts/kconfig/qconf, which is unneeded for external module builds
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# - GCC plugins, which will not work on the installed system even after
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# being rebuilt.
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#
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# Use the single-target build to avoid the modpost invocation, which
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# would overwrite Module.symvers.
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"${MAKE}" HOSTCC="${CC}" KBUILD_EXTMOD="${destdir}" scripts/
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cat <<-'EOF' > "${destdir}/scripts/Kbuild"
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subdir-y := basic
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hostprogs-always-y := mod/modpost
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mod/modpost-objs := $(addprefix mod/, modpost.o file2alias.o sumversion.o symsearch.o)
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EOF
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# Run once again to rebuild scripts/basic/ and scripts/mod/modpost.
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"${MAKE}" HOSTCC="${CC}" KBUILD_EXTMOD="${destdir}" scripts/
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rm -f "${destdir}/Kbuild" "${destdir}/scripts/Kbuild"
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fi
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find "${destdir}" \( -name '.*.cmd' -o -name '*.o' \) -delete
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