code review 5975060: 5l, runtime: remove softfloat emulation code when not used

5l, runtime: remove softfloat emulation code when not used
This leads to ~30kB improvement on code size for ARM machines with VFP/NEON.
Example: go test -c math
       GOARM=5  GOARM=6
  Old: 1884200  1839144
  New: 1884165  1805245
  -:        35    33899

[minux1, 2012-04-02 13:48:41]

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com),

I'd like you to review this change to
https://code.google.com/p/go/

[minux1, 2012-04-02 16:44:45]

I've tested this CL on Pandaboard ES (dual-core Cortex-A9) and QEMU emulated
ARM9E.

[rsc, 2012-04-02 16:58:49]

How do you run under QEMU?  That hasn't worked for me for a long time.
What version do you use?  Do you build it from source or use a
pre-compiled package?

[minux1, 2012-04-02 17:09:49]

On Tue, Apr 3, 2012 at 12:58 AM, Russ Cox <rsc@golang.org> wrote:

> How do you run under QEMU?  That hasn't worked for me for a long time.
> What version do you use?  Do you build it from source or use a
> pre-compiled package?
>
I used qemu as a full system emulator, not user qemu.
I think I will look into issue 1508 soon.

[bradfitz, 2012-04-02 17:11:20]

On Mon, Apr 2, 2012 at 10:09 AM, minux <minux.ma@gmail.com> wrote:

>
> On Tue, Apr 3, 2012 at 12:58 AM, Russ Cox <rsc@golang.org> wrote:
>
>> How do you run under QEMU?  That hasn't worked for me for a long time.
>> What version do you use?  Do you build it from source or use a
>> pre-compiled package?
>>
> I used qemu as a full system emulator, not user qemu.


I was trying that out again this morning.  I found it painfully slow, even
on an i7.

How long is your all.bash?  What qemu-system-arm flags do you use?



> I think I will look into issue 1508 soon.
>

[minux1, 2012-04-02 18:29:39]

On Tue, Apr 3, 2012 at 1:11 AM, Brad Fitzpatrick <bradfitz@golang.org>wrote:
>
> On Mon, Apr 2, 2012 at 10:09 AM, minux <minux.ma@gmail.com> wrote:
>>
>> On Tue, Apr 3, 2012 at 12:58 AM, Russ Cox <rsc@golang.org> wrote:
>>
>>> How do you run under QEMU?  That hasn't worked for me for a long time.
>>> What version do you use?  Do you build it from source or use a
>>> pre-compiled package?
>>>
>> I used qemu as a full system emulator, not user qemu.
>
>
> I was trying that out again this morning.  I found it painfully slow, even
> on an i7.
> How long is your all.bash?  What qemu-system-arm flags do you use?
>
It *is* so sloooow. It took me 6700s to run the all.bash.
I use "qemu-system-arm -m 256 -M versatilepb", but I think different -cpu
settings might affect
performance.

[bradfitz, 2012-04-02 18:31:37]

On Mon, Apr 2, 2012 at 11:29 AM, minux <minux.ma@gmail.com> wrote:

>
>
> On Tue, Apr 3, 2012 at 1:11 AM, Brad Fitzpatrick <bradfitz@golang.org>wrote:
>>
>> On Mon, Apr 2, 2012 at 10:09 AM, minux <minux.ma@gmail.com> wrote:
>>>
>>> On Tue, Apr 3, 2012 at 12:58 AM, Russ Cox <rsc@golang.org> wrote:
>>>
>>>> How do you run under QEMU?  That hasn't worked for me for a long time.
>>>> What version do you use?  Do you build it from source or use a
>>>> pre-compiled package?
>>>>
>>> I used qemu as a full system emulator, not user qemu.
>>
>>
>> I was trying that out again this morning.  I found it painfully slow,
>> even on an i7.
>> How long is your all.bash?  What qemu-system-arm flags do you use?
>>
> It *is* so sloooow. It took me 6700s to run the all.bash.
> I use "qemu-system-arm -m 256 -M versatilepb", but I think different -cpu
> settings might affect
> performance.
>

Okay, that's the same as I saw/used.  I was hoping you knew of secret flags
to make it bearable.

[minux1, 2012-04-02 18:40:41]

On Tue, Apr 3, 2012 at 2:31 AM, Brad Fitzpatrick <bradfitz@golang.org>wrote:
>
> On Mon, Apr 2, 2012 at 11:29 AM, minux <minux.ma@gmail.com> wrote:
>>
>> On Tue, Apr 3, 2012 at 1:11 AM, Brad Fitzpatrick <bradfitz@golang.org>wrote:
>>>
>>> On Mon, Apr 2, 2012 at 10:09 AM, minux <minux.ma@gmail.com> wrote:
>>>>
>>>> On Tue, Apr 3, 2012 at 12:58 AM, Russ Cox <rsc@golang.org> wrote:
>>>>
>>>>> How do you run under QEMU?  That hasn't worked for me for a long time.
>>>>> What version do you use?  Do you build it from source or use a
>>>>> pre-compiled package?
>>>>>
>>>> I used qemu as a full system emulator, not user qemu.
>>>
>>> I was trying that out again this morning.  I found it painfully slow,
>>> even on an i7.
>>> How long is your all.bash?  What qemu-system-arm flags do you use?
>>>
>> It *is* so sloooow. It took me 6700s to run the all.bash.
>> I use "qemu-system-arm -m 256 -M versatilepb", but I think different -cpu
>> settings might affect
>> performance.
>>
>
> Okay, that's the same as I saw/used.  I was hoping you knew of secret
> flags to make it bearable.
>
I think the most suitable way is to use user mode emulation, and I haven't
tried to optimize the performance
of system mode emulation (I only use it to test FP emulation).

[dave_cheney.net, 2012-04-08 02:58:42]

LGTM. 

I've tested this on arm5 and arm6. All math{,/*} tests pass.

[minux1, 2012-04-08 10:01:51]

Let me give some explanation for each of the TODO removed.

http://codereview.appspot.com/5975060/diff/2001/src/cmd/5l/obj.c
File src/cmd/5l/obj.c (left):

http://codereview.appspot.com/5975060/diff/2001/src/cmd/5l/obj.c#oldcode253
src/cmd/5l/obj.c:253: // TODO(kaib): this doesn't work, the prog can't be found
in runtime
Let me explain the TODO here.

The mark() could work, the reason that it doesn't work is that
The symbols 'runtime.softfloat' and 'math.sqrtGoC' don't exist.

Also, because it uses lookup(), which means that if the requested
symbol doesn't exist, it will create one, so the symbol passed to
mark() isn't S (nil), and it will appear mark() doesn't work.

I changed lookup() to rlookup(), which won't create the symbol
if not found, and this will avoid this problem should it arise in
the future.

http://codereview.appspot.com/5975060/diff/2001/src/pkg/runtime/asm_arm.s
File src/pkg/runtime/asm_arm.s (left):

http://codereview.appspot.com/5975060/diff/2001/src/pkg/runtime/asm_arm.s#old...
src/pkg/runtime/asm_arm.s:63: // TODO(kaib): remove these once i actually
understand how the linker removes symbols
our dead code removal is working properly now, so don't need to pull
in these functions explicitly.

BTW, in runtime, we use _div and _mod, so again we don't need to pull
them in here.

[rsc, 2012-04-10 19:36:09]

LGTM

[minux1, 2012-04-10 20:14:48]

Submitted as
https://code.google.com/p/go/source/detail?r=8f08ef4568b2528b849de2dc39a8b7a3...

My hg crashed (httplib.IncompleteRead: IncompleteRead(31 bytes read)) while
submitting.