code review 9778046: runtime: use m and g, instead of R9 and R10, in ARM ass...

runtime: use m and g, instead of R9 and R10, in ARM assembly files
also don't clobber R9 if it is about to crash.

In response to https://codereview.appspot.com/9251043/#msg2.

[minux1, 2013-05-27 13:13:16]

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/

[khr, 2013-05-28 06:11:30]

LGTM

[khr1, 2013-05-28 06:13:01]

By the way, is there any way to outlaw using R9 and R10 explicitly?  I can
see someone writing assembly and clobbering these without realizing they
hold g/m.


On Mon, May 27, 2013 at 11:11 PM, <khr@golang.org> wrote:

> LGTM
>
>
https://codereview.appspot.**com/9778046/<https://codereview.appspot.com/9778...
>

[dave_cheney.net, 2013-05-28 06:18:08]

> By the way, is there any way to outlaw using R9 and R10 explicitly?  I can
> see someone writing assembly and clobbering these without realizing they
> hold g/m.

Nope, there are no safety guards. R11 also needs to be used with care
as the linker will assume it is free for temporary use if required.

[minux1, 2013-05-28 12:06:52]

On Tue, May 28, 2013 at 2:13 PM, Keith Randall <khr@google.com> wrote:

> By the way, is there any way to outlaw using R9 and R10 explicitly?  I can
> see someone writing assembly and clobbering these without realizing they
> hold g/m.
>
no. we have at least two bugs originating from R9/R10 being clobbered.

https://codereview.appspot.com/6300043
https://codereview.appspot.com/6305100

the original author assumes temporarily clobber r9/r10 is ok, but it turns
out
signal can be deliver to a thread while executing memset/memmove.

I'd like a way for the linker to warn any such uses, but i don't know how to
exclude some cases where it's necessary to touch r9/r10 (perhaps using
a whilelist of function names?)

[minux1, 2013-05-28 12:13:20]

*** Submitted as https://code.google.com/p/go/source/detail?r=e4db68a39f50 ***

runtime: use m and g, instead of R9 and R10, in ARM assembly files
also don't clobber R9 if it is about to crash.

In response to https://codereview.appspot.com/9251043/#msg2.

R=golang-dev, khr, khr, dave
CC=golang-dev
https://codereview.appspot.com/9778046