Fixes create_sdk target for cross-builds.

Fixes create_sdk target for cross-builds.

Building an sdk requires snapshots to be generated for
pub, analyzer, dart2js, etc. using a Dart VM binary that
has been built for the host. Currently, when we cross-build,
we do not build a Dart VM binary for the host.

Rather than monkey with the gyp files to do that, this
change modifies build.py to explicitly build:
1. The create_sdk target for the host arch,
2. The runtime target for the target arch,
After which files are copied to create a dart-sdk
directory for the target archetecture.

After this change, we *should* be able to cross-build Debian
packages for arm, which I'll work on in a subsequent change.

R=iposva@google.com, whesse@google.com

Committed: https://code.google.com/p/dart/source/detail?r=38337

[zra, 2014-07-15 23:15:52]

https://codereview.chromium.org/397593006/diff/1/tools/build.py
File tools/build.py (right):

https://codereview.chromium.org/397593006/diff/1/tools/build.py#newcode472
tools/build.py:472: def BuildCrossSdk(options, target_os, mode, arch):
This is where the new stuff is.

[Ivan Posva, 2014-07-16 05:46:03]

+whesse

The CL in general LGTM, but two things make me slightly nervous:
- How do we ensure that the "runtime" target is the only target which does
generate binaries.
- Are we sure no platform-dependent data is captured in the snapshot.

The second point is less of an issue for Linux/Linux cross builds, but might
surface in other scenarios.

-Ivan

https://codereview.chromium.org/397593006/diff/1/tools/build.py
File tools/build.py (right):

https://codereview.chromium.org/397593006/diff/1/tools/build.py#newcode474
tools/build.py:474: if BuildOneConfig(options, 'create_sdk', HOST_OS, mode,
HOST_ARCH, False) != 0:
Long Life

[Bill Hesse, 2014-07-16 07:35:43]

The target "samples" builds "runtime/dart-runtime.gyp:sample_extension", which
is a binary shared library.  There is also test_extension, built by "runtime",
which is a shared library.

We can discuss if this should be changed.

https://codereview.chromium.org/397593006/diff/1/tools/utils.py
File tools/utils.py (right):

https://codereview.chromium.org/397593006/diff/1/tools/utils.py#newcode247
tools/utils.py:247: if ((GetArchFamily(host_arch) != GetArchFamily(arch)) or
Why not just return the boolean expression?

[zra, 2014-07-16 14:48:21]

I'm not sure I understand Ivan's first concern. The Dart VM binary is the only
binary file copied into dart-sdk by the create_sdk.py script, as far as I can
tell.

As for the second concern, I can try doing a native build of create_sdk on one
of the arm boards, but that would still be Linux->Linux. For Linux->Android,
probably all I could do is run e.g. dart2js with a snapshot built this way on a
device and see what happens.

https://codereview.chromium.org/397593006/diff/1/tools/build.py
File tools/build.py (right):

https://codereview.chromium.org/397593006/diff/1/tools/build.py#newcode474
tools/build.py:474: if BuildOneConfig(options, 'create_sdk', HOST_OS, mode,
HOST_ARCH, False) != 0:
On 2014/07/16 05:46:02, Ivan Posva wrote:
> Long Life

Done.

https://codereview.chromium.org/397593006/diff/1/tools/utils.py
File tools/utils.py (right):

https://codereview.chromium.org/397593006/diff/1/tools/utils.py#newcode247
tools/utils.py:247: if ((GetArchFamily(host_arch) != GetArchFamily(arch)) or
On 2014/07/16 07:35:43, Bill Hesse wrote:
> Why not just return the boolean expression?

Done.

[Bill Hesse, 2014-07-17 09:20:26]

LGTM.

[zra, 2014-07-17 16:54:59]

On 2014/07/16 14:48:21, zra wrote:
> As for the second concern, I can try doing a native build of create_sdk on one
> of the arm boards, but that would still be Linux->Linux. For Linux->Android,
> probably all I could do is run e.g. dart2js with a snapshot built this way on
a
> device and see what happens.

I have checked, and pub and dart2js from SDKs built like this work on Raspberry
Pi, and Beaglebone Black, and dart2js runs on Android. I'm not sure how I would
go about verifying for certain that no platform specific stuff is leaking into
the snapshots, but I've added a TODO for that in build.py.

[zra, 2014-07-17 18:05:46]

Committed patchset #3 manually as r38337 (presubmit successful).