code review 6846057: cmd/8l: fix data corruption for MULB SI,

cmd/8l: fix data corruption for MULB SI,

The 8l linker automatically inserts XCHG instructions
to support otherwise impossible byte registers
(only available on AX, BX, CX, DX).

Sometimes AX or DX is needed (for MUL and DIV) so
we need to avoid clobbering them.

[remyoudompheng, 2012-11-15 07:22:52]

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

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

[remyoudompheng, 2012-11-16 20:50:13]

ping?

[dfc, 2012-11-16 23:49:50]

This fixed the bug that your walkdiv CL exposed. If this CL mirrors a similar
provision on 6l then LGTM. A

On 17/11/2012, at 7:50, remyoudompheng@gmail.com wrote:

> ping?
> 
> http://codereview.appspot.com/6846057/

[remyoudompheng, 2012-11-17 00:10:47]

On 2012/11/17 Dave Cheney <dave@cheney.net> wrote:
> This fixed the bug that your walkdiv CL exposed. If this CL mirrors a similar
provision on 6l then LGTM. A

In 64-bit mode all registers have a byte variant so the same logic is
not necessary. However, 6l has a 32-bit mode, which I think we don't
use, and the fix could make sense there too.

Rémy.

[remyoudompheng, 2012-11-17 00:30:42]

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

Please take another look.

[dfc, 2012-11-19 23:45:11]

ping, iant ?

[remyoudompheng, 2012-11-25 21:27:09]

ping?

[iant2, 2012-11-26 01:47:26]

This is for rsc, I don't know this code.

http://codereview.appspot.com/6846057/

[rsc, 2012-11-26 02:38:14]

I'm catching up, really I am! :-)

[remyoudompheng, 2012-11-26 20:31:52]

*** Submitted as http://code.google.com/p/go/source/detail?r=1470920a2804 ***

cmd/8l: fix data corruption for MULB SI,

The 8l linker automatically inserts XCHG instructions
to support otherwise impossible byte registers
(only available on AX, BX, CX, DX).

Sometimes AX or DX is needed (for MUL and DIV) so
we need to avoid clobbering them.

R=golang-dev, dave, iant, iant, rsc
CC=golang-dev
http://codereview.appspot.com/6846057