code review 42880043: cmd/gc: implement -pack flag

cmd/gc: implement -pack flag

The -pack flag causes 5g, 6g, 8g to write a Go archive directly,
instead of requiring the use of 'go tool pack' to convert the .5/.6/.8
to .a format.

Writing directly avoids the copy and also avoids having the
export data stored twice in the archive (once in __.PKGDEF,
once in .5/.6/.8).

A separate CL will enable the use of this flag by cmd/go.

Other build systems that do not know about -pack will be unaffected.

The changes to cmd/ld handle a minor simplification to the format:
an unused section is removed.

[rsc, 2013-12-16 18:08:06]

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

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

[iant, 2013-12-16 20:57:51]

LGTM

https://codereview.appspot.com/42880043/diff/40001/src/cmd/gc/obj.c
File src/cmd/gc/obj.c (right):

https://codereview.appspot.com/42880043/diff/40001/src/cmd/gc/obj.c#newcode23
src/cmd/gc/obj.c:23: snprint(arhdr, ArhdrSize, "%-16s%-12d%-6d%-6d%-8o%-10d`",
The current go pack writes 0644 in the mode field, so this is a change, though
presumably a harmless one.

https://codereview.appspot.com/42880043/diff/40001/src/cmd/gc/obj.c#newcode51
src/cmd/gc/obj.c:51: dumpexport();
Very minor difference: go pack doesn't put the "// exports" comment in the
PKGDEF; this will.

[rsc, 2013-12-18 02:31:09]

https://codereview.appspot.com/42880043/diff/40001/src/cmd/gc/obj.c
File src/cmd/gc/obj.c (right):

https://codereview.appspot.com/42880043/diff/40001/src/cmd/gc/obj.c#newcode23
src/cmd/gc/obj.c:23: snprint(arhdr, ArhdrSize, "%-16s%-12d%-6d%-6d%-8o%-10d`",
On 2013/12/16 20:57:52, iant wrote:
> The current go pack writes 0644 in the mode field, so this is a change, though
> presumably a harmless one.

Changed to 0644, here and in cmd/dist and cmd/go.

https://codereview.appspot.com/42880043/diff/40001/src/cmd/gc/obj.c#newcode51
src/cmd/gc/obj.c:51: dumpexport();
On 2013/12/16 20:57:52, iant wrote:
> Very minor difference: go pack doesn't put the "// exports" comment in the
> PKGDEF; this will.

Thanks. I think I'm okay with that. I guess we'll see if it causes any problems.

[rsc, 2013-12-18 02:43:38]

*** Submitted as https://code.google.com/p/go/source/detail?r=92e348edc9ce ***

cmd/gc: implement -pack flag

The -pack flag causes 5g, 6g, 8g to write a Go archive directly,
instead of requiring the use of 'go tool pack' to convert the .5/.6/.8
to .a format.

Writing directly avoids the copy and also avoids having the
export data stored twice in the archive (once in __.PKGDEF,
once in .5/.6/.8).

A separate CL will enable the use of this flag by cmd/go.

Other build systems that do not know about -pack will be unaffected.

The changes to cmd/ld handle a minor simplification to the format:
an unused section is removed.

R=iant, r
CC=golang-dev
https://codereview.appspot.com/42880043