code review 146130043: runtime: fix runtime.Breakpoint on ARMv5

runtime: fix runtime.Breakpoint on ARMv5

Fixes issue 8775.

Use the illegal instruction suggested by Ian in https://codereview.appspot.com/144180043/#msg4 on all arm arches.

[dave_cheney.net, 2014-09-23 02:23:18]

Hello golang-codereviews@googlegroups.com,

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

[gobot, 2014-09-23 02:42:15]

R=rsc@golang.org (assigned by dave@cheney.net)

[minux, 2014-09-23 03:32:03]

i think iant said that the software bkpt instruction used by arm is always
the same, and if that's the case, just always use that one? does the
undefined inst. work on armv6 and armv7?

[dave_cheney.net, 2014-09-23 04:26:21]

> i think iant said that the software bkpt instruction used by arm is always
> the same, and if that's the case, just always use that one? does the
> undefined inst. work on armv6 and armv7?

Bingo!

$ go build bkpt.go

dfc@qnap:~/src$ ./bkpt

SIGTRAP: trace trap

PC=0x3fca0

That works on arm5,

(gdb) r

Starting program: /home/dfc/src/bkpt


Program received signal SIGTRAP, Trace/breakpoint trap.

runtime.breakpoint () at /home/dfc/go/src/runtime/asm_arm.s:95

95 // so you must manually "set $pc+=4" to skip it and continue.

I'll test that it works on arm6+ and update my CL as appropriate.

[dave_cheney.net, 2014-09-23 04:34:36]

Hello golang-codereviews@googlegroups.com, gobot@golang.org, rsc@golang.org (cc:
golang-codereviews@googlegroups.com, iant@golang.org, minux@golang.org),

Please take another look.

[minux, 2014-09-23 05:09:15]

LGTM. Thanks.

[dave_cheney.net, 2014-09-23 05:35:57]

*** Submitted as https://code.google.com/p/go/source/detail?r=35193bf04a5b ***

runtime: fix runtime.Breakpoint on ARMv5

Fixes issue 8775.

Use the illegal instruction suggested by Ian in
https://codereview.appspot.com/144180043/#msg4 on all arm arches.

LGTM=minux
R=golang-codereviews, gobot, rsc
CC=golang-codereviews, iant, minux
https://codereview.appspot.com/146130043

[dave_cheney.net, 2014-09-23 05:39:44]

Thanks for baring with me on this.

On Tue, Sep 23, 2014 at 3:35 PM,  <dave@cheney.net> wrote:
> *** Submitted as
> https://code.google.com/p/go/source/detail?r=35193bf04a5b ***
>
> runtime: fix runtime.Breakpoint on ARMv5
>
> Fixes issue 8775.
>
> Use the illegal instruction suggested by Ian in
> https://codereview.appspot.com/144180043/#msg4 on all arm arches.
>
> LGTM=minux
> R=golang-codereviews, gobot, rsc
> CC=golang-codereviews, iant, minux
> https://codereview.appspot.com/146130043
>
>
> https://codereview.appspot.com/146130043/