Review request: Zero buildsystem changes

[Gary Benson]

Hi all,

Zero is an interpreter-only port of HotSpot that uses no assembler and
can trivially be built on any Linux system.  The following two webrevs
add Zero support to OpenJDK:

  http://cr.openjdk.java.net/~gbenson/zero-11-build/
  http://cr.openjdk.java.net/~gbenson/zero-11-hotspot/

The bulk of the changes are in the zero-11-hotspot webrev, which has
been through a couple of review cycles and is (hopefully!) about to
be tested with JPRT and pushed.

The zero-11-build webrev contains a small number of changes, mostly
to makefiles, that are required in order to build OpenJDK with Zero.
Is this the right list to review these changes?

Cheers,
Gary

-- 
http://gbenson.net/
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Build Instructions
==================

There are a number of environment variables that need setting before
running make, but if you are using jdk/make/jdk_generic_profile.sh
to set up your environment then you only need to set one, and a build
can be as simple as:

  export ZERO_BUILD=true
  . jdk/make/jdk_generic_profile.sh
  gmake sanity && gmake

The mandatory environment variable does the following:

  ZERO_BUILD
    Setting ZERO_BUILD to "true" will cause the Zero interpreter to
    be used.  If ZERO_BUILD is unset, or set to any other value than
    "true", the standard, platform-specific interpreter will be used.

Of the other environment variables the following are required when
ZERO_BUILD is set to "true".  These are set by
jdk/make/jdk_generic_profile.sh based on the result of uname -m:

  ZERO_LIBARCH
    This is the name of the architecture-specific subdirectory under
    $JAVA_HOME/jre/lib.  Typically this will be the same as the output
    of uname -m, although there are some exceptions: "amd64" instead
    of "x86_64", for example, and "i386" instead of "i686".

  ZERO_ARCHDEF
    The value of ZERO_ARCHDEF will be passed to the C++ compiler using
    -D${ZERO_ARCHDEF} to allow conditionalized platform-specific code.
    This is typically set to ZERO_LIBARCH converted to uppercase but,
    again, there are exceptions.  "i386" becomes "IA32", to match what
    HotSpot already does, and on platforms with both 32- and 64-bit
    variants ZERO_ARCHDEF corresponds to the 32-bit version, so both
    ppc and ppc64 have ZERO_ARCHDEF set to "PPC".

  ZERO_ENDIANNESS
    This is set to "little" or "big".

  ARCH_DATA_MODEL
    This is set to "32" or "64".

  ZERO_ARCHFLAG
    This is a flag that will be passed to the C++ compiler and to the
    linker to instruct them to generate code for the particular
    platform.  This is required for platforms with both 32- and 64-bit
    variants where the compiler needs to be told which variant to
    build for.  ZERO_ARCHFLAG will typically be set to "-m32" or
    "-m64", except on 31-bit zSeries where it will be set to "-m31".

Zero uses one external library, libffi, for JNI method invocation.
The following two variables are used to tell the compiler and linker
how to find libffi.  These can be set by the user, but if left unset
then jdk/make/jdk_generic_profile.sh will attempt to set them using
pkg-config or, failing that, by supplying defaults pointing to the
standard locations:

  LIBFFI_CFLAGS
    Flags to be passed to the C++ compiler to build against libffi.
    If unset (and pkg-config is not installed, or if libffi is not
    built with pkg-config) then this defaults to "".

  LIBFFI_LIBS
    Flags to be passed to the linker to link against libffi.  If
    unset (and pkg-config is not installed, or if libffi is not
    built with pkg-config) then this defaults to "-lffi".