os/user: Lookup fails to find users when running as root on darwin-arm64 cross compiled from darwin-amd64

[JBirdVegas]

What version of Go are you using (go version)?

$ go version
go version go1.16beta1 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

Compiled using darwin, amd64. Executed on darwin, arm64

Build env:

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/user-js/Library/Caches/go-build"
GOENV="/Users/user-js/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/user-js/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/user-js/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/user-js/go/go1.16beta1"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/user-js/go/go1.16beta1/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.16beta1"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/s6/fv1xpj4n7j9c9l1flw1j4lxr0000gn/T/go-build580121957=/tmp/go-build -gno-record-gcc-switches -fno-common"
GOROOT/bin/go version: go version go1.16beta1 darwin/amd64
GOROOT/bin/go tool compile -V: compile version go1.16beta1
uname -v: Darwin Kernel Version 19.6.0: Thu Oct 29 22:56:45 PDT 2020; root:xnu-6153.141.2.2~1/RELEASE_X86_64
ProductName:	Mac OS X
ProductVersion:	10.15.7
BuildVersion:	19H15
lldb --version: lldb-1200.0.41
Apple Swift version 5.3.1 (swiftlang-1200.0.41 clang-1200.0.32.8)
gdb --version: GNU gdb (GDB) 8.3

Execution env:

go env Output

$ go env
GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="/Users/user-es/Library/Caches/go-build"
GOENV="/Users/user-es/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/user-es/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/user-es/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/opt/homebrew/Cellar/go/1.15.6/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/homebrew/Cellar/go/1.15.6/libexec/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.16beta1"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/v1/1y48b2yx6tndh56_yn2fqx4c0000gn/T/go-build161273293=/tmp/go-build -gno-record-gcc-switches -fno-common"
GOROOT/bin/go version: go version go1.16beta1 darwin/arm64
GOROOT/bin/go tool compile -V: compile version go1.16beta1
uname -v: Darwin Kernel Version 20.1.0: Sat Oct 31 00:07:10 PDT 2020; root:xnu-7195.50.7~2/RELEASE_ARM64_T8101
ProductName:	macOS
ProductVersion:	11.0.1
BuildVersion:	20B29
lldb --version: lldb-1200.0.44.2
Apple Swift version 5.3.2 (swiftlang-1200.0.45 clang-1200.0.32.28)

### What did you do?

cross compile code on darwin amd64 then execute on darwin arm64.

% cat main.go
package main

import (
	"log"
	"os"
	"os/user"
	"runtime"
)

func main() {
	log.Printf("GOOS: %s, GOARCH: %s", runtime.GOOS, runtime.GOARCH)
	lookup, err := user.Lookup(os.Args[1])
	if err != nil {
		log.Panic(err)
	}
	log.Printf("User: %v\n", lookup)
}

Compile on darwin amd64 for arm64
GOOS=darwin GOARCH=arm64 go build main.go

Download to darwin arm64 computer then execute without and with sudo.

% whoami
user-es
% ./main $(whoami)
2021/01/06 09:08:50 GOOS: darwin, GOARCH: arm64
2021/01/06 09:08:50 User: &{501 20 user-es  /Users/user-es}
% sudo ./main $(whoami)
2021/01/06 09:08:50 GOOS: darwin, GOARCH: arm64
2021/01/06 09:08:50 user: unknown user user-es
panic: user: unknown user user-es

goroutine 1 [running]:
log.Panic(0x1400010ff38, 0x1, 0x1)
	/Users/user-js/go/go1.16beta1/src/log/log.go:354 +0x98
main.main()
	/Users/user-js/dev/go1.16beta1-maybebug/main.go:14 +0xe8

What did you expect to see?

I expected the user user-es found by the function user.Lookup(string) when running as root, same as it does without root.

I also expected the same error when the code is compiled on darwin-arm64 and executed on darwin-arm64. However if compiled on the target machine the function user.Lookup(string) works as expected when ran as both user and root.

What did you see instead?

The function user.Lookup(string) fails to find the user user-es when running as root, when cross compiled from darwin-amd64.

[bcmills]

CC @cherrymui

[ianlancetaylor]

You probably have to set CGO_ENABLED=1. But that may fail due to #43476.

[JBirdVegas]

Yes @ianlancetaylor that is correct however building with CGO_ENABLED=0 produces the same error.

#43476 refers to building on arm64 and executing on amd64. My error is the opposite, GOHOSTARCH=amd64 GOARCH=arm64

[ianlancetaylor]

To be clear, I'm suggesting that you need to build with CGO_ENABLED=1. The default is CGO_ENABLED=0.

[whess96]

Building w/ CGO enabled should work. However, the os/user docco claims to provide "pure go" implementations for when cgo is disabled and when the osusergo build tag is enabled. Unfortunately the pure go implementation directly parses the /etc/passwd file which doesn't work on darwin 😕.

Since cgo can be a real cross-compilation headache, a pure go implementation for darwin would be extremely convenient.