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

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)?

issue に記載されている configure および make コマンドで x64-to-arm ビルドを再現する。まず deps/v8/include/v8config.h と生成された out/tools/v8_gypfiles/v8_libplatform.host.mk から始め、続いてなぜ host オブジェクトが ARM target マクロを受け取るのかを追跡する。対応している cross-build の手順と、必要な guard またはビルド生成の動作が文書化され、検証されていれば完了とする。