code review 5650066: cgo: add support for returning errno with gccgo.

cgo: add support for returning errno with gccgo.

Also eliminate some warnings in builds.

[remyoudompheng, 2012-02-12 10:26:53]

Hello iant@google.com, golang-dev@googlegroups.com (cc:
golang-dev@googlegroups.com, remy@archlinux.org),

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

[remyoudompheng, 2012-02-12 12:16:45]

Hello iant@google.com, golang-dev@googlegroups.com (cc:
golang-dev@googlegroups.com, remy@archlinux.org),

Please take another look.

[albert.strasheim, 2012-02-12 12:27:24]

On 2012/02/12 12:16:45, remyoudompheng wrote:
> Hello mailto:iant@google.com, mailto:golang-dev@googlegroups.com (cc:
> mailto:golang-dev@googlegroups.com, mailto:remy@archlinux.org),
> 
> Please take another look.

Could you please include the fix from

http://groups.google.com/group/golang-nuts/msg/180b05e59922b2eb

too? The cgo changes fix my problem. Thanks. :-)

[iant, 2012-02-12 19:17:29]

http://codereview.appspot.com/5650066/diff/3004/src/cmd/cgo/out.go
File src/cmd/cgo/out.go (right):

http://codereview.appspot.com/5650066/diff/3004/src/cmd/cgo/out.go#newcode279
src/cmd/cgo/out.go:279: fmt.Fprintf(fgo2, "\tr, errno := %s(%s)\n", cname,
strings.Join(paramnames, ", "))
I think you are making this more complicated than it needs to be.  I think you
can just do
    r := CNAME(PARAMS)
    return r, syscall.GetErrno()

[remyoudompheng, 2012-02-13 22:15:43]

http://codereview.appspot.com/5650066/diff/3004/src/cmd/cgo/out.go
File src/cmd/cgo/out.go (right):

http://codereview.appspot.com/5650066/diff/3004/src/cmd/cgo/out.go#newcode279
src/cmd/cgo/out.go:279: fmt.Fprintf(fgo2, "\tr, errno := %s(%s)\n", cname,
strings.Join(paramnames, ", "))
That looks interesting. I can't find GetErrno in the standard Go library. Do you
plan to keep it in gccgo's version of syscall package?

[remyoudompheng, 2012-02-13 23:12:23]

Hello iant@google.com, golang-dev@googlegroups.com, fullung@gmail.com,
iant@golang.org (cc: golang-dev@googlegroups.com, remy@archlinux.org),

Please take another look.

[iant2, 2012-02-14 05:08:02]

FYI

remyoudompheng@gmail.com writes:

> That looks interesting. I can't find GetErrno in the standard Go
> library. Do you plan to keep it in gccgo's version of syscall package?

Yes, gccgo needs it.  The gccgo library doesn't make direct syscalls as
the gc library does.  It calls into the regular libc functions.  That
means that it doesn't get an errno value back as a return value, it
needs to read the C variable errno.  Since this issue arises for other
code that calls into libc, such as the os/user package, the GetErrno
function is exported from the syscall package.  (There is also
syscall.SetErrno.)

Ian

[iant, 2012-02-14 05:27:54]

LGTM

but see what rsc thinks

[rsc, 2012-02-14 16:25:52]

LGTM

Thanks very much for working on this.

[remyoudompheng, 2012-02-14 19:24:08]

*** Submitted as http://code.google.com/p/go/source/detail?r=b330eb5c9e6c ***

cgo: add support for returning errno with gccgo.

Also eliminate some warnings in builds.

R=golang-dev, fullung, iant, rsc
CC=golang-dev, remy
http://codereview.appspot.com/5650066