Is there a way to execute functions in a compiled golang binary from another binary without needing any special setup?

Question

I have a RPC type of setup where one binary (binaryA) is requesting work to be done from another binary (binaryB). They're both compiled the same way and are on the same system. I can't shell out to binaryA because the task involved involves a lot of data which would take too long to serialize and I can't use a golang plugin because the I want to be able to call functions without needing to create a special binary.

This is roughly the setup I'm trying to achieve:

binaryA compiled with go build mainA.go . Somewhere in that binary, this file is compiled:

package demo
import "fmt"

func TestFn(){
    fmt.Println("binaryA")
    func(){ someFn() }()
}

I want to be able to call TestFn() and that anonymous function with binaryB.

Here's what I have so far.

import (
    "debug/macho"
    "fmt"
    "os"
    "reflect"
    "unsafe"
)

func main() {
    filename := "binaryA"
    f, _ := os.Open(filename)
    defer f.Close()

    mf, _ := macho.NewFile(f)

    sym2Addr := make(map[string]uintptr)
    for _, sym := range mf.Symtab.Syms {
        if int(sym.Sect-1) >= len(mf.Sections) || 
           mf.Sections[sym.Sect-1].Seg != "__TEXT" { continue }
        value := uintptr(sym.Value)
        sym2Addr[sym.Name] = value
    }

    funcType := reflect.TypeOf(func() {})
    if testFnPtr, ok := sym2Addr["main.TestFn"]; ok {
        TestFn := reflect.New(funcType).Elem()
        p := new(uintptr)
        *p = testFnPtr
        *(*unsafe.Pointer)(unsafe.Pointer(TestFn.Addr().Pointer())) = unsafe.Pointer(p)
        TestFn.Call([]reflect.Value{})
    }
}

Using the code above I'm able to find the symbol main.TestFn but it ultimately fails with:

unexpected fault address 0x210d0fb1
fatal error: fault
[signal SIGBUS: bus error code=0x2 addr=0x210d0fb1 pc=0x210d0fb1]

goroutine 1 [running]:
runtime.throw(...)
        .asdf/installs/golang/1.15/go/src/runtime/panic.go:1116 
runtime.sigpanic()
        .asdf/installs/golang/1.15/go/src/runtime/signal_unix.go:717
runtime.call32(...)
        .asdf/installs/golang/1.15/go/src/runtime/asm_amd64.s:540 
reflect.Value.call(...)
        .asdf/installs/golang/1.15/go/src/reflect/value.go:475 
reflect.Value.Call(...)
        .asdf/installs/golang/1.15/go/src/reflect/value.go:336
main.main()
        plugin_demo.go:106
runtime.main()
        .asdf/installs/golang/1.15/go/src/runtime/proc.go:204
runtime.goexit()
        .asdf/installs/golang/1.15/go/src/runtime/asm_amd64.s:1374
exit status 2

EDIT: I can recompile binaryA with any build flags I want.

Answer 1

Is there a way to execute functions in a compiled golang binary from another binary without needing any special setup?

No, that simply is not how compiled (to machine code) programs work (in any language).