[Buildroot] Golang in buildroot

Hey Nic,

On Tue, Jul 28, 2015 at 9:11 PM Nic Dade [off-list ref] wrote:

I saw your patch
  https://patchwork.ozlabs.org/patch/497914/
and thought I'd try it.

I found that I had to make some changes to make all the pieces work.

Cool. We have a newer version of this patch now, that Yann and I have been
working on. You can find it here:
https://github.com/paralin/buildroot/commit/826a3bea5b828d4fc08e0bb48ab78a3094204d85

Yann actually has done some more work on the patch as well which I'll bring
into my repo soon.

First, the 'install -D ...' line in GOLANG_INSTALL_TARGET_CMD...

See the updated patch.

Secondly I wanted to build a go cross compiler to run on the host. The
patch mentions this, and golang.mk seems to cover it, but without a
Config.in.host file and a BR2_PACKAGE_HOST_GOLANG buidroot option it can't
be activated.  So added a Config.in.host.

This isn't necessary - if your packages need the go cross compiler, add a
dependency (in the makefile and not in the Config.in) to host-golang. IF
you want to build one to use without a package, just type "make
host-golang".

In golang.mk I added "CGO_ENABLED=1" to the make.bash calls. By default (in

go 1.4) CGO is disabled by default in cross compilers. That might not be
important for your case, but I want the C<->Go interworking support for my
purposes. I don't think it adds anything to the runtime unless you use CGO
in the code, so you might enable it all the time.

This isn't necessary. With the current patch I'm building Docker, which
uses CGO extensively, for ARM. You just need to specify CGO_ENABLED=1 in
the compilation of your Go code.

Lastly I am targeting an ARM without an FPU, so when I go cross-compile I

must also pass in GOARM=5 (along with the usual GOARCH=arm). I haven't
found a clean way to separate GOARM from the rest of the golang.mk. It
doesn't belong in golang.mk since it is target specific. Where should it
go?

See the updated patch.

I hacked together a new variable GOLANGENV which contains the environment

variable definitions needed by other packages to cross compile.
GOLANGENV=CC_FOR_TARGET="$(TARGET_CC)" ....
since the list gets long and I don't want it repeated in each go-using
package.

Not sure this is entirely necessary, it might be important to have these be
specifically set in each package where they are used. But it's a decent
idea @Yann.

The patches to buildroot which I apply on top of your match are attached,

as well as a complete package/golang/ for clarity.

Thank you, but I can't apply these changes so easily to our new patch.
Please see the updates, rebase, and email them back. I'll give it a test
tomorrow!

Best,
Christian
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