When configuring the hotspot build the build system sets up the ARCH variable to reflect the target cpu. Currently the value is initialized to OPENJDK_TARGET_CPU_LEGACY, which is the internal legacy cpu name. For example, on x86 64-bit this is amd64 on linux (but x86_64 on mac).

Depending on the platform ARCH is either honored or ignored. Solaris for example overrides the value of ARCH with the output from 'uname -p' (see hotspot/make/solaris/makefiles/defs.make). On BSD/OSX the value is also overidden, but with the output from 'uname -m' (see hotspot/make/bsd/makefiles/defs.make). Windows is.. different.

On Linux the ARCH variable is honored, but if it is *not* set it is initialized to the output from 'uname -m' (see hotspot/make/linux/makefiles/defs.make).

The goal in the new (JDK) build system is to have the "legacy" value gradually removed in favor of the other variables. We should move towards setting ARCH to OPENJDK_TARGET_CPU_ARCH instead of OPENJDK_TARGET_CPU_LEGACY and make sure the Hotspot build system picks it up correctly.