Cross-build x64 host -> arm target fails in V8 host arch guard (v8config.h)

[rebroad]

Summary

Cross-building Node.js for --dest-cpu=arm (32-bit ARM / armhf) from an x64 Linux host fails in V8 host object compilation due to a host/target architecture guard in deps/v8/include/v8config.h.

Environment

• Host: Ubuntu 24.04 x86_64
• Target: Raspberry Pi 3, 32-bit Raspbian Buster (armhf)
• Cross toolchain: arm-linux-gnueabihf-*

Repro

From x64 host:

./configure \
  --dest-os=linux \
  --dest-cpu=arm \
  --cross-compiling \
  --with-arm-float-abi=hard \
  --with-arm-fpu=neon \
  --without-node-snapshot
make -j1

Failure

Host V8 compilation fails with:

#error Target architecture arm is only supported on arm and ia32 host

Coming from deps/v8/include/v8config.h:

#if (V8_TARGET_ARCH_ARM && !(V8_HOST_ARCH_IA32 || V8_HOST_ARCH_ARM))
#error Target architecture arm is only supported on arm and ia32 host
#endif

In generated host makefiles (for example out/tools/v8_gypfiles/v8_libplatform.host.mk), host objects are compiled with -DV8_TARGET_ARCH_ARM, which triggers this guard on x64 hosts.

Notes

• --without-node-snapshot does not avoid this, as host V8 objects are still built with ARM target macros.
• A local workaround changing the guard to include x64 host allows compilation to proceed:

-#if (V8_TARGET_ARCH_ARM && !(V8_HOST_ARCH_IA32 || V8_HOST_ARCH_ARM))
+#if (V8_TARGET_ARCH_ARM && !(V8_HOST_ARCH_IA32 || V8_HOST_ARCH_ARM || V8_HOST_ARCH_X64))

Request

What is the intended/supported path for x64-host -> arm-target cross-builds in current Node/V8?

If this should be supported, could build generation be adjusted so host-side V8 tools/objects do not fail this guard (or guard logic updated in a supported way)?

[joyeecheung]

x64 -> armv7 cross compilation on RHEL8 is tested in the CI which simply uses

/usr/bin/python3 ./configure --verbose  --dest-cpu=arm

https://ci.nodejs.org/job/node-cross-compile/nodes=cross-compiler-rhel8-armv7-gcc-10-glibc-2.28/56776/consoleText

You might want to check if this works, if it does maybe remove some of the configure options to figure out which one is causing the incompatibility, or if it's a tool chain problem. The CI uses

+++ export PKG_CONFIG_PATH=/opt/rh/gcc-toolset-10/root/usr/lib64/pkgconfig
+++ PKG_CONFIG_PATH=/opt/rh/gcc-toolset-10/root/usr/lib64/pkgconfig
++ export 'CC_host=ccache gcc -m32'
++ CC_host='ccache gcc -m32'
++ export 'CXX_host=ccache g++ -m32'
++ CXX_host='ccache g++ -m32'
++ export 'CC=ccache /opt/raspberrypi/rpi-newer-crosstools/x64-gcc-10.3.0-glibc-2.28/arm-rpi-linux-gnueabihf/bin/arm-rpi-linux-gnueabihf-gcc -march=armv7-a'
++ CC='ccache /opt/raspberrypi/rpi-newer-crosstools/x64-gcc-10.3.0-glibc-2.28/arm-rpi-linux-gnueabihf/bin/arm-rpi-linux-gnueabihf-gcc -march=armv7-a'
++ export 'CXX=ccache /opt/raspberrypi/rpi-newer-crosstools/x64-gcc-10.3.0-glibc-2.28/arm-rpi-linux-gnueabihf/bin/arm-rpi-linux-gnueabihf-g++ -march=armv7-a'
++ CXX='ccache /opt/raspberrypi/rpi-newer-crosstools/x64-gcc-10.3.0-glibc-2.28/arm-rpi-linux-gnueabihf/bin/arm-rpi-linux-gnueabihf-g++ -march=armv7-a'
+ export 'CC_target=ccache /opt/raspberrypi/rpi-newer-crosstools/x64-gcc-10.3.0-glibc-2.28/arm-rpi-linux-gnueabihf/bin/arm-rpi-linux-gnueabihf-gcc -march=armv7-a'
+ CC_target='ccache /opt/raspberrypi/rpi-newer-crosstools/x64-gcc-10.3.0-glibc-2.28/arm-rpi-linux-gnueabihf/bin/arm-rpi-linux-gnueabihf-gcc -march=armv7-a'
+ export 'CXX_target=ccache /opt/raspberrypi/rpi-newer-crosstools/x64-gcc-10.3.0-glibc-2.28/arm-rpi-linux-gnueabihf/bin/arm-rpi-linux-gnueabihf-g++ -march=armv7-a'
+ CXX_target='ccache /opt/raspberrypi/rpi-newer-crosstools/x64-gcc-10.3.0-glibc-2.28/arm-rpi-linux-gnueabihf/bin/arm-rpi-linux-gnueabihf-g++ -march=armv7-a'
+ echo 'Compiling with GCC 10-glibc-2.28'
Compiling with GCC 10-glibc-2.28
+ ccache /opt/raspberrypi/rpi-newer-crosstools/x64-gcc-10.3.0-glibc-2.28/arm-rpi-linux-gnueabihf/bin/arm-rpi-linux-gnueabihf-gcc -march=armv7-a --version
arm-rpi-linux-gnueabihf-gcc (crosstool-NG 1.25.0) 10.3.0
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[joyeecheung]

Actually I forgot that armv7 support has be demoted to exprimental since v24: #58071 in the CI, only older LTS are still tested. arm64 is still supported (as in, it's tested in the CI and volunteers will try to make sure it still builds for every release). It got demoted because it was blocking a V8 upgrade that was already difficult. I think the support status can be concluded as: if you want to see armv7 fixed in versions >= 24, please submit a patch. Otherwise, the volunteers who can barely keep the more popular platform support afloat won't have more free time to fix it.