code review 6855088: cmd/6l, cmd/8l: emit no-ops to separate zero-stack func...

cmd/6l, cmd/8l: emit no-ops to separate zero-stack funcs from nosplits.

The stack overflow checker in the linker uses the spadj field
to determine whether stack space will be large enough or not.
When spadj=0, the checker treats the function as a nosplit
and emits an error although the program is correct.

Also enable the stack checker in 8l.

Fixes issue 4316.

[remyoudompheng, 2012-11-25 11:45:20]

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

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

[rsc, 2012-11-26 15:44:40]

LGTM

I was confused still and had to read the stkcheck code. Please make the comment

// zero-byte stack adjustment.
// Insert a fake non-zero adjustment so that stkcheck can
// recognize the end of the stack-splitting prolog.

[remyoudompheng, 2012-11-26 20:51:53]

*** Submitted as http://code.google.com/p/go/source/detail?r=6bfa10936597 ***

cmd/6l, cmd/8l: emit no-ops to separate zero-stack funcs from nosplits.

The stack overflow checker in the linker uses the spadj field
to determine whether stack space will be large enough or not.
When spadj=0, the checker treats the function as a nosplit
and emits an error although the program is correct.

Also enable the stack checker in 8l.

Fixes issue 4316.

R=rsc, golang-dev
CC=golang-dev
http://codereview.appspot.com/6855088