code review 4223044: ld: weak symbols

ld: weak symbols

A reference to the address of weak.foo resolves at link time
to the address of the symbol foo if foo would end up in the
binary anyway, or to zero if foo would not be in the binary.

For example:

        int xxx = 1;
        int yyy = 2;
        int weak·xxx;
        int weak·yyy;

        void main·main(void) {
                runtime·printf("%p %p %p\n", &xxx, &weak·xxx, &weak·yyy);
        }

prints the same non-nil address twice, then 0 (because yyy is not
referenced so it was dropped from the binary).

This will be used by the reflection tables.

[rsc, 2011-02-24 05:49:47]

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

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

[iant, 2011-02-24 12:40:51]

LGTM

http://codereview.appspot.com/4223044/diff/4001/src/cmd/ld/lib.h
File src/cmd/ld/lib.h (right):

http://codereview.appspot.com/4223044/diff/4001/src/cmd/ld/lib.h#newcode170
src/cmd/ld/lib.h:170: void	undef(void);
Should doweak be declared here as well?

[rsc, 2011-02-24 21:43:36]

On Thu, Feb 24, 2011 at 07:40,  <iant@golang.org> wrote:
> Should doweak be declared here as well?

nice catch, thanks.

[rsc, 2011-02-24 21:45:51]

*** Submitted as http://code.google.com/p/go/source/detail?r=b0e4832734b3 ***

ld: weak symbols

A reference to the address of weak.foo resolves at link time
to the address of the symbol foo if foo would end up in the
binary anyway, or to zero if foo would not be in the binary.

For example:

        int xxx = 1;
        int yyy = 2;
        int weak·xxx;
        int weak·yyy;

        void main·main(void) {
                runtime·printf("%p %p %p\n", &xxx, &weak·xxx, &weak·yyy);
        }

prints the same non-nil address twice, then 0 (because yyy is not
referenced so it was dropped from the binary).

This will be used by the reflection tables.

R=iant
CC=golang-dev
http://codereview.appspot.com/4223044