I'm trying to cross-compile a macOS binary in Docker with the cgo DNS
resolver enabled. My understanding is that this is doable without setting
up a full macOS SDK toolchain, and by using the package from the macOS
distribution. However, I'm unable to make it work. Somehow the compiler
always rebuilds the net package from sources and the netgo DNS resolver
becomes the de facto.
Very short implementation I'm using for testing:
package main
import "net"
func main() {
net.LookupIP("google.com")
}
The build output shows that net.a is built from sources instead of picking
up /usr/local/go/pkg/darwin_amd64/net.a:
$ ls -la /usr/local/go/pkg/darwin_amd64/net.a
-rw-r--r-- 1 root root 1241304 Jun 6 23:51
/usr/local/go/pkg/darwin_amd64/net.a
$ go clean -cache
$ go build -x -o dns-test ./dns
WORK=/tmp/go-build098597944
mkdir -p $WORK/b002/
cat >$WORK/b002/importcfg << 'EOF' # internal
# import config
importmap golang_org/x/net/route=vendor/golang_org/x/net/route
packagefile context=/usr/local/go/pkg/darwin_amd64/context.a
packagefile errors=/usr/local/go/pkg/darwin_amd64/errors.a
packagefile
vendor/golang_org/x/net/route=/usr/local/go/pkg/darwin_amd64/vendor/golang_org/x/net/route.a
packagefile
internal/nettrace=/usr/local/go/pkg/darwin_amd64/internal/nettrace.a
packagefile internal/poll=/usr/local/go/pkg/darwin_amd64/internal/poll.a
packagefile
internal/singleflight=/usr/local/go/pkg/darwin_amd64/internal/singleflight.a
packagefile io=/usr/local/go/pkg/darwin_amd64/io.a
packagefile math/rand=/usr/local/go/pkg/darwin_amd64/math/rand.a
packagefile os=/usr/local/go/pkg/darwin_amd64/os.a
packagefile runtime=/usr/local/go/pkg/darwin_amd64/runtime.a
packagefile sort=/usr/local/go/pkg/darwin_amd64/sort.a
packagefile sync=/usr/local/go/pkg/darwin_amd64/sync.a
packagefile sync/atomic=/usr/local/go/pkg/darwin_amd64/sync/atomic.a
packagefile syscall=/usr/local/go/pkg/darwin_amd64/syscall.a
packagefile time=/usr/local/go/pkg/darwin_amd64/time.a
EOF
cd /usr/local/go/src/net
/usr/local/go/pkg/tool/linux_amd64/compile -o $WORK/b002/_pkg_.a -trimpath
$WORK/b002 -p net -std -buildid _tpOUnWlUki4sCfaeRYL/_tpOUnWlUki4sCfaeRYL
-goversion go1.10.3 -D "" -importcfg $WORK/b002/importcfg -pack -c=4
./addrselect.go ./cgo_stub.go ./conf.go ./dial.go ./dnsclient.go
./dnsclient_unix.go ./dnsconfig_unix.go ./dnsmsg.go ./error_posix.go
./fd_unix.go ./file.go ./file_unix.go ./hook.go ./hook_unix.go ./hosts.go
./interface.go ./interface_bsd.go ./interface_darwin.go ./ip.go
./iprawsock.go ./iprawsock_posix.go ./ipsock.go ./ipsock_posix.go
./lookup.go ./lookup_unix.go ./mac.go ./net.go ./nss.go ./parse.go
./pipe.go ./port.go ./port_unix.go ./rawconn.go ./sendfile_stub.go
./sock_bsd.go ./sock_posix.go ./sockopt_bsd.go ./sockopt_posix.go
./sockoptip_bsdvar.go ./sockoptip_posix.go ./sys_cloexec.go ./tcpsock.go
./tcpsock_posix.go ./tcpsockopt_darwin.go ./tcpsockopt_posix.go
./udpsock.go ./udpsock_posix.go ./unixsock.go ./unixsock_posix.go
./writev_unix.go
/usr/local/go/pkg/tool/linux_amd64/buildid -w $WORK/b002/_pkg_.a # internal
cp $WORK/b002/_pkg_.a
/root/.cache/go-build/71/71d5652836fbf72132d2864101b08cfb7dc5657beaa4cd0804e7d893646a3d60-d
# internal
mkdir -p $WORK/b001/
cat >$WORK/b001/importcfg << 'EOF' # internal
# import config
packagefile net=$WORK/b002/_pkg_.a
packagefile runtime=/usr/local/go/pkg/darwin_amd64/runtime.a
EOF
cd /workspace/src/go.example.com/dns
/usr/local/go/pkg/tool/linux_amd64/compile -o $WORK/b001/_pkg_.a -trimpath
$WORK/b001 -p main -complete -buildid
t_6XipuZQQ3V_Rlugib8/t_6XipuZQQ3V_Rlugib8 -goversion go1.10.3 -D ""
-importcfg $WORK/b001/importcfg -pack -c=4 ./main.go
/usr/local/go/pkg/tool/linux_amd64/buildid -w $WORK/b001/_pkg_.a # internal
cp $WORK/b001/_pkg_.a
/root/.cache/go-build/35/35e87cb5622549aaa8a434a32334706a5b3862ff7d49ce9daf3b29ba88094f41-d
# internal
cat >$WORK/b001/importcfg.link << 'EOF' # internal
packagefile go.example.com/dns=$WORK/b001/_pkg_.a
packagefile net=$WORK/b002/_pkg_.a
packagefile runtime=/usr/local/go/pkg/darwin_amd64/runtime.a
packagefile context=/usr/local/go/pkg/darwin_amd64/context.a
packagefile errors=/usr/local/go/pkg/darwin_amd64/errors.a
packagefile
vendor/golang_org/x/net/route=/usr/local/go/pkg/darwin_amd64/vendor/golang_org/x/net/route.a
packagefile
internal/nettrace=/usr/local/go/pkg/darwin_amd64/internal/nettrace.a
packagefile internal/poll=/usr/local/go/pkg/darwin_amd64/internal/poll.a
packagefile
internal/singleflight=/usr/local/go/pkg/darwin_amd64/internal/singleflight.a
packagefile io=/usr/local/go/pkg/darwin_amd64/io.a
packagefile math/rand=/usr/local/go/pkg/darwin_amd64/math/rand.a
packagefile os=/usr/local/go/pkg/darwin_amd64/os.a
packagefile sort=/usr/local/go/pkg/darwin_amd64/sort.a
packagefile sync=/usr/local/go/pkg/darwin_amd64/sync.a
packagefile sync/atomic=/usr/local/go/pkg/darwin_amd64/sync/atomic.a
packagefile syscall=/usr/local/go/pkg/darwin_amd64/syscall.a
packagefile time=/usr/local/go/pkg/darwin_amd64/time.a
packagefile
runtime/internal/atomic=/usr/local/go/pkg/darwin_amd64/runtime/internal/atomic.a
packagefile
runtime/internal/sys=/usr/local/go/pkg/darwin_amd64/runtime/internal/sys.a
packagefile fmt=/usr/local/go/pkg/darwin_amd64/fmt.a
packagefile reflect=/usr/local/go/pkg/darwin_amd64/reflect.a
packagefile math=/usr/local/go/pkg/darwin_amd64/math.a
packagefile
internal/testlog=/usr/local/go/pkg/darwin_amd64/internal/testlog.a
packagefile internal/race=/usr/local/go/pkg/darwin_amd64/internal/race.a
packagefile strconv=/usr/local/go/pkg/darwin_amd64/strconv.a
packagefile unicode/utf8=/usr/local/go/pkg/darwin_amd64/unicode/utf8.a
packagefile unicode=/usr/local/go/pkg/darwin_amd64/unicode.a
packagefile internal/cpu=/usr/local/go/pkg/darwin_amd64/internal/cpu.a
EOF
mkdir -p $WORK/b001/exe/
cd .
/usr/local/go/pkg/tool/linux_amd64/link -o $WORK/b001/exe/a.out -importcfg
$WORK/b001/importcfg.link -buildmode=exe
-buildid=6-oHCWY8Z57CMNCfUB-n/t_6XipuZQQ3V_Rlugib8/9dtyWN9RKHU5XwbNrmpr/6-oHCWY8Z57CMNCfUB-n
-extld=gcc $WORK/b001/_pkg_.a
/usr/local/go/pkg/tool/linux_amd64/buildid -w $WORK/b001/exe/a.out #
internal
cp $WORK/b001/exe/a.out dns-test
rm -r $WORK/b001/
This didn't work as the netgo DNS resolver is the one used:
$ otool -L ./dns-test
./dns-test:
$ GODEBUG=netdns=2 ./dns-test
go package net: built with netgo build tag; using Go's DNS resolver
go package net: hostLookupOrder(google.com) = files,dns
Any ideas what I am doing wrong?
Thanks,
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