Reflection with module

[CrookedCrane]

What version of Garble and Go are you using?

$ garble version
0.4.0
$ go version
go1.17 windows/amd64

What environment are you running Garble on?

go env Output

$ go env
set GO111MODULE=on
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\CrookedCrane\AppData\Local\go-build
set GOENV=C:\Users\CrookedCrane\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=C:\Users\CrookedCrane\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\CrookedCrane\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=C:\Users\CrookedCrane\sdk\go1.17
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=C:\Users\CrookedCrane\sdk\go1.17\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.17
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=C:\Users\CrookedCrane\sdk\go1.17\src\main\go.mod
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\CrookedCrane\AppData\Local\Temp\go-build3937438513=/tmp/go-build -gno-record-gcc-switches

What did you do?

run binary built from

main.go

package main
import (

"fmt"

struc "main/structure"

"reflect"

)
func GetMyStructInformation(input interface{}) (strOut string, numOut int) {

ptr := reflect.ValueOf(input)

value := reflect.Indirect(ptr)

strOut = value.FieldByName("MyString").String()

numOut = int(value.FieldByName("MyNumber").Int())

return

}
func main() {

myItem := &struc.MyStruct{MyString: "This is a string", MyNumber: 1000}

_ = reflect.ValueOf(myItem)

str, num := GetMyStructInformation(myItem)

fmt.Println("The string is: ", str)

fmt.Println("The number is: ", num)

}

struct.go

package structure
type MyStruct struct {

MyString string

MyNumber int

}

project structure

main
|_____structure
         |_____struct.go
|_____go.mod
|_____main.go

What did you expect to see?

The string is:  This is a string
The number is:  1000

What did you see instead?

panic: reflect: call of reflect.Value.Int on zero Value

goroutine 1 [running]:
reflect.Value.Int(...)
        reflect/value.go:1334
main.GetMyStructInformation({0x152640, 0xc000004078})
        IgTaaCXu.go:1 +0x1a5
main.main()
        qB1_pSpU.go:1 +0xad

I noticed in the source code to ignore objects for obfuscation they must be declared and their reflection usage must be in the same package, and indeed when I move MyStruct's declaration into main.go it gives the inteded output. Since my project relies on a lot of plugins and reflection, can there be a way to make it happen cross packages?

[mvdan]

For better or worse, Go builds one package at a time, and so we obfuscate one package at a time as well.

When we obfuscate main/structure, we have no knowledge of uses of reflection yet.

The alternative would be to analyze the entire package graph before starting the build. This would be very inefficient for large builds though, and would affect our ability to rely on the build cache for speed. So it doesn't feel like the right decision.

[CrookedCrane]

So for this particular case (heavy use of cross package reflection), can I create a sort of objects-to-ignore list, like knownReflectAPIs but for objects to tell garble to ignore them?

[mvdan]

The easiest way is to do something like:

package structure

// MyStruct is used via reflection in other packages. Let garble know.
var _ = reflect.TypeOf(MyStruct{})

type MyStruct struct {
    [...]
}

It's also nice because you annotate that information right next to the type definition.

[mvdan]

#409 documents the suggestion above again.

#406 is about improving these edge cases automatically in the future.