cmd/ld: Objective-C dynamic relocation link failure with internal linker on Mac OS X 10.6 with Xcode 4.2

[andlabs]

(This is somewhat related to issue #5699 but I was told to file a new one; things got
more interesting since.)

$ cat a.go
package main; import "fmt"
// #cgo LDFLAGS: -framework Foundation -framework AppKit
// extern void *cgoptr;
import "C"
func main() { fmt.Printf("pointer from cgo: %p\n", C.cgoptr) }
$ cat a.m
#include <AppKit/NSKeyValueBinding.h>
void *cgoptr = &NSObservedObjectKey;

All of the following:

$ CC=gcc   CGO_ENABLED=1 GOARCH=amd64 go build -x
$ CC=gcc   CGO_ENABLED=1 GOARCH=386   go build -x
$ CC=clang CGO_ENABLED=1 GOARCH=amd64 go build -x
$ CC=clang CGO_ENABLED=1 GOARCH=386   go build -x

will yield the following during the final link:

main(__DATA/__data): unexpected reloc for dynamic symbol NSObservedObjectKey
main(__DATA/__data): unhandled relocation for NSObservedObjectKey (type 32 rtype 1)

This happens for any Objective-C anything.

For larger projects, the link failures become more spectacular. Attached are the results
of building
andlabs/ui@93914ec (this
specific commit) with a modified cmd/ld that does not terminate after 20 error messages
(this should probably be an option like it is for the compilers but I'll leave that for
another issue). I don't know why the 386 one has a different error from the rest; it
should probably be a third issue...

go version:
go version devel +b10044024a6d Thu May 15 15:55:31 2014 +1000 darwin/amd64

gcc version:
i686-apple-darwin10-llvm-gcc-4.2 (GCC) 4.2.1 (Based on Apple Inc. build 5658) (LLVM
build 2336.1.00)
Copyright (C) 2007 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

clang version:
Apple clang version 3.0 (tags/Apple/clang-211.10.1) (based on LLVM 3.0svn)
Target: x86_64-apple-darwin10.8.0
Thread model: posix

This is with Xcode 4.2 for Snow Leopard.

Thanks.

Attachments:

1. newerr.386 (10200 bytes)
2. newerr.amd64 (17599 bytes)

[andlabs]

Comment 1:

As another example, consider
$ cat b.go
package main; import "fmt"
// #cgo LDFLAGS: -framework Foundation
// extern void *cgoptr(void);
import "C"
func main() { fmt.Printf("pointer from cgo: %p\n", C.cgoptr()) }
$ cat b.m
#include <Foundation/NSObject.h>
void *cgoptr(void) { return [NSObject new]; }
which yields
main(__DATA/__objc_classrefs): unexpected reloc for dynamic symbol OBJC_CLASS_$_NSObject
main(__DATA/__objc_classrefs): unhandled relocation for OBJC_CLASS_$_NSObject (type 32
rtype 1)
I also forgot to say that things work fine with -linkmode external, as with issue #5699.

[ianlancetaylor]

Comment 2:

Labels changed: added repo-main, release-go1.4.

[rsc]

Comment 3:

The real question for me is why this is not using linkmode external in the first place.
Linkmode internal is supposed to be used only for the standard library.
Are you forcing linkmode internal somehow?

Status changed to Accepted.

[rsc]

Comment 4:

Not going to get to this for 1.4. Sorry.

Labels changed: added release-go1.5, removed release-go1.4.