code review 5601044: cgo: Linux/ARM support *PREVIEW*

cgo: Linux/ARM support *PREVIEW*
     This is an unfinished preview for testers. Not for merging.

Current status:
1. all pkg tests and tests in test/ directory are passed.
2. all but one tests in misc/cgo are passed.
   misc/cgo/test used to fail when GOMAXPROCS>1 on SMP ARM machines, but I believe this is fixed now.
3. cmd/go can handle cgo programs now.

Known issues:
1. No thumb library support, you have to make sure your external library is compiled using '-marm'.
2. The ELF Dynamic linker is hard coded to be /lib/ld-linux.so.3, so on some
distributions, like recent Ubuntu and Android, you might need to adjust
src/cmd/5l/asm.c. I plan to add auto detection for this.

Note:
1. You have to export CGO_ENABLED=1 by yourself. (Update: enabled in Patch
Set 5)
2. At this time, it will take some time to set up enviroment to do the tests in misc/cgo. Mainly because the recent removal/rename of some scripts/commands (e.g. quietgcc, gotest; gopack -> pack)
(Update: the restriction is removed in Patch Set 6)

[minux1, 2012-01-30 16:12:11]

Hello krautz@gmail.com, dave@cheney.net (cc: golang-dev@googlegroups.com),

I'd like you to review this change to
https://go.googlecode.com/hg/

[rsc, 2012-01-30 16:14:03]

Very nice, thanks for working on this.
We probably won't be able to review this until
after Go 1 is out, but I have updated issue 1880
to point at this CL.  Please remind us about this
after the Go 1 release.

Thanks.
Russ

[minux1, 2012-02-05 21:14:10]

PTAL. Also rebased to the latest tip.

Go callbacks from C is now working. The only remaining problem is some data
races on SMP
machines.

All tests passed when GOMAXPROCS=1.

[minux1, 2012-02-10 10:52:09]

I wonder how to properly support cgo on Android.

Android's bionic libc uses a different dynamic linker, so either we must
have
a way to pass option to 5l or we have to hardcode the dynamic linker path in
5l, and auto detect which to use.

The latter option isn't perfect, because it makes cross compiling for
Android
on PC very difficult. But the first option isn't perfect either, users are
forced
to set environment vars or set unfamiliar cmdline options.

Yet another option is to treat Android as an new OS, at least for 5l. This
is the
most flexible way, but will bring a lot of code duplication.

[rsc, 2012-02-14 18:52:55]

Let's postpone this discussion until after Go 1.

[minux1, 2012-03-30 17:35:01]

On 2012/02/14 18:52:55, rsc wrote:
> Let's postpone this discussion until after Go 1.
I think we can discuss this CL now.

Should I split this CL into several small parts?

[rsc, 2012-04-02 15:32:49]

Splitting the CL into more easily digested chunks would be great.

Thanks.
Russ

[dave_cheney.net, 2012-04-06 12:22:18]

Hello, 

This latest CL appears to make the Go 1 API check go into an infinite loop.

[minux1, 2012-04-06 21:05:54]

On 2012/04/06 12:22:18, dfc wrote:
> This latest CL appears to make the Go 1 API check go into an infinite loop.
Strange. the cmd/api does take a long time to finish, but the whole ./all.bash
takes less than 30 minutes to finish on 700MHz Pandaboard ES.

[dave_cheney.net, 2012-04-06 21:42:30]

Maybe I didn't give it enough time, I will try again. 

Sent from my iPad

On 07/04/2012, at 7:05, minux.ma@gmail.com wrote:

> On 2012/04/06 12:22:18, dfc wrote:
>> This latest CL appears to make the Go 1 API check go into an infinite
> loop.
> Strange. the cmd/api does take a long time to finish, but the whole
> ./all.bash
> takes less than 30 minutes to finish on 700MHz Pandaboard ES.
> 
> http://codereview.appspot.com/5601044/

[dave_cheney.net, 2012-04-06 22:55:11]

Correction, I was too impatient. go tool api completes without incident if you
are patient

[minux1, 2012-04-07 19:34:27]

I've splited this CL into five parts.
The first two are the most difficult parts.

Thanks to our new build infrastructure, except for the last one, I think each
could be reviewed
and submitted in isolation.

CL 5991065: cmd/5l, cmd/ld: dynamic linking library support
CL 5989057: runtime: cgo support for Linux/ARM
CL 5991066: cmd/cgo: support Linux/ARM
CL 5989058: cmd/go: cgo for Linux/ARM
CL 5988057: go/build: cgo is supported on Linux/ARM