code review 7432048: cmd/cgo: use explicit flag to emit dynamic linker path

cmd/cgo: use explicit flag to emit dynamic linker path

Using -import_runtime_cgo would have worked great except
that it doesn't get passed to the second invocation of cgo,
and that's the one that writes the relevant file.

Fixes ARM build on systems with a different dynamic linker
than the one 5l assumes (like Gentoo).

[rsc, 2013-03-01 19:53:59]

Hello golang-dev@googlegroups.com,

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

[minux1, 2013-03-01 19:58:10]

please see my comment in https://codereview.appspot.com/7433043/#msg7.

if we want to distribute cgo-enabled arm binary distributions, we should
diagnose
mismatches in dynlinker pragma.

perhaps we should always determine that at final link time.

[rsc, 2013-03-04 14:58:40]

PTAL (nothing changed)

I believe that this CL is fine as is. I understand the situation you bring
up, but:

1) If the only cgo packages involved are the ones in the standard library
(net and os/user, and then by implication runtime/cgo) then the dynlinker
pragmas will match, and there will be no detection of the invalid value.
Recording it in net and os/user would not change this outcome.

2) If other cgo packages are involved, the default behavior will be to tell
6l to invoke gcc to put the binary together, in which case the dynlinker
pragma is ignored and gcc will (presumably) use an appropriate value.
Recording it in non-standard packages would not change this outcome.

Russ

[minux1, 2013-03-04 16:13:48]

LGTM.

On Mon, Mar 4, 2013 at 10:58 PM, Russ Cox <rsc@golang.org> wrote:

> 1) If the only cgo packages involved are the ones in the standard library
> (net and os/user, and then by implication runtime/cgo) then the dynlinker
> pragmas will match, and there will be no detection of the invalid value.
> Recording it in net and os/user would not change this outcome.
>
yeah, i was proposing we determine dynlinker until final link time to fix
this problem however,
i still can't find a way to get that info without using gcc.

[rsc, 2013-03-04 16:23:21]

*** Submitted as https://code.google.com/p/go/source/detail?r=f545866390ab ***

cmd/cgo: use explicit flag to emit dynamic linker path

Using -import_runtime_cgo would have worked great except
that it doesn't get passed to the second invocation of cgo,
and that's the one that writes the relevant file.

Fixes ARM build on systems with a different dynamic linker
than the one 5l assumes (like Gentoo).

R=golang-dev, minux.ma
CC=golang-dev
https://codereview.appspot.com/7432048