MIPS: Fix mips gyp build for chromium.

MIPS: Fix mips gyp build for chromium.

Our planned CL for the Chromium build system passes the toolchain
vars though the Makefiles, so that we do not depend on $CXX, etc.,
in the environment.

That causes a problem with deriving the 'm32flag' in v8 gyp.

This patch lets us build with or without the toolchain vars in
the environment.

BUG=

Committed: http://code.google.com/p/v8/source/detail?r=13695

[Paul Lind, 2013-02-12 04:11:44]

Hi Jakob - Fixing a case where the m32 flag is passed incorrectly to the mips
cross toolchain when the CXX vars are not in the environment. PTAL, and let me
know if you have a better approach.

[Jakob Kummerow, 2013-02-12 12:29:47]

Sorry, I don't like this change. It adds a very non-intuitive condition -- I'm
not sure I fully understand the implications even after thinking about it for
several minutes. Further, I'm concerned that this breaks ia32 Chromium
compilation on x64 systems (haven't tested it, though, because the build
environment for that is a bit involved to set up).

Could you tell me more about your proposed changes to configure the compiler
"through the Makefiles"? Is the new system based on GYP variables? If so, it
should be possible to use that information directly, either as input to the
feature detection shell command, or to avoid calling that command altogether.

[Paul Lind, 2013-02-13 07:52:25]

On 2013/02/12 12:29:47, Jakob wrote:
> Sorry, I don't like this change. It adds a very non-intuitive condition -- 

I understand your objection, I don't much like the 2nd line of this patch
either.

What we are trying to do is avoid setting the toolchain vars in the environment,
and instead have them set via GYP variables. And it works, EXCEPT for the
setting of the compiler flags, which this patch is trying to address.

The Chromium src/build/common.gypi has the changes for mips at r179820
(eb5f167). Currently I have my Chromium tree pulled at r181996 (for the
following line # refs).

At src/build/common.gypi line 3970 we set GYP vars for the toolchain:
['target_arch=="mipsel"', {
  'make_global_settings': [
    ['CC', '<(sysroot)/../bin/mipsel-linux-gnu-gcc'],
    ['CXX', '<(sysroot)/../bin/mipsel-linux-gnu-g++'],
    ['LINK', '$(CXX)'],
    ['CC.host', '<!(which gcc)'],
    ['CXX.host', '<!(which g++)'],
    ['LINK.host', '<!(which g++)'],
  ],
}],

We made this similar to the previous OS=="android" section, which has the
comment:
    # Hardcode the compiler names in the Makefile so that
    # it won't depend on the environment at make time.
which seems like a good idea.

When the top-level Makefile is generated the toolchain paths are set there:
CXX = $(abspath
/opt/paul/chrome/2-mips-chrome/src/native_client/toolchain/linux_mips-trusted/sysroot/../bin/mipsel-linux-gnu-g++)

This toolchain is used for v8 build, but since we do not have $CXX in the
environment, we don't calculate 'mipscompiler' var correctly, so we miss
necessary mips gcc flags, AND we also erroneously pick up the m32flag (-m32).

Any suggestions for how to properly set those flags based on the GYP vars we do
have would be greatly appreciated.

I'll send you a email with a patch to build our toolchain in the Chromium tree
should you wish to go that far. Everything else is present in Chromium source.

thanks,

paul

[Paul Lind, 2013-02-13 16:39:09]

I should have also mentioned that for non-Chromium builds of v8, we do like the
toolchain vars in the environment, it is a very convenient way to set up
cross-builds.

So we are attempting support use of either mode:  env vars or gyp vars. The
current patch does this.

[Paul Lind, 2013-02-19 02:11:35]

Jakob, your version works perfectly. We've made corresponding changes for
Chromium gyp, and will upstream that as soon as this lands. Thanks a lot for
your help!

[Jakob Kummerow, 2013-02-19 08:52:32]

LGTM, I'll land this.

[Jakob Kummerow, 2013-02-19 15:22:17]

Committed patchset #2 manually as r13695 (presubmit successful).