cmd/cgo: improve cgoCheckResult error message

When an unpinned Go pointer is returned to a C function, this error shows up:

panic: runtime error: cgo result is unpinned Go pointer or points to unpinned Go pointer

> goroutine 17 [running, locked to thread]:
> panic({0x78fa15d1e5c0?, 0xc00001e050?})
>         /usr/lib/go/src/runtime/panic.go:802 +0x168
> runtime.cgoCheckArg(0x78fa15d1bf20, 0xc000066e50, 0x0?, 0x0, {0x78fa15cfaa62, 0x42})
>         /usr/lib/go/src/runtime/cgocall.go:679 +0x35b
> runtime.cgoCheckResult({0x78fa15d1bf20, 0xc000066e50})
>         /usr/lib/go/src/runtime/cgocall.go:795 +0x4b
> _cgoexp_1ff3739d54a6_foo(0x7fff7f7b0220)
>         _cgo_gotypes.go:65 +0x5d
> runtime.cgocallbackg1(0x78fa15cf16c0, 0x7fff7f7b0220, 0x0)
>         /usr/lib/go/src/runtime/cgocall.go:446 +0x289
> runtime.cgocallbackg(0x78fa15cf16c0, 0x7fff7f7b0220, 0x0)
>         /usr/lib/go/src/runtime/cgocall.go:350 +0x132
> runtime.cgocallbackg(0x78fa15cf16c0, 0x7fff7f7b0220, 0x0)
>         <autogenerated>:1 +0x2b
> runtime.cgocallback(0x0, 0x0, 0x0)
>         /usr/lib/go/src/runtime/asm_amd64.s:1082 +0xcd
> runtime.goexit({})
>         /usr/lib/go/src/runtime/asm_amd64.s:1693 +0x1

_cgoexp_1ff3739d54a6_foo is the faulty caller; it is not obvious to
find it in the stack trace.

Retrieve the caller name, and use it in the error message:

panic: runtime error: result of cgo function foo is unpinned Go pointer or points to unpinned Go pointer

> goroutine 17 [running, locked to thread]:
> panic({0x7feae6c50640?, 0x26fcc9896000?})
>         /mnt/go/src/runtime/panic.go:877 +0x16f
> runtime.cgoCheckArg(0x7feae6c4dee0, 0x26fcc9774e50, 0x0?, 0x0, {0x26fcc9894000, 0x52})
>         /mnt/go/src/runtime/cgocall.go:678 +0x35b
> runtime.cgoCheckResult({0x7feae6c4dee0, 0x26fcc9774e50})
>         /mnt/go/src/runtime/cgocall.go:797 +0x85
> _cgoexp_9ed4cd31b2e5_foo(0x7ffcc89baf10)
>         _cgo_gotypes.go:65 +0x5d
> runtime.cgocallbackg1(0x7feae6c1d340, 0x7ffcc89baf10, 0x0)
>         /mnt/go/src/runtime/cgocall.go:446 +0x289
> runtime.cgocallbackg(0x7feae6c1d340, 0x7ffcc89baf10, 0x0)
>         /mnt/go/src/runtime/cgocall.go:350 +0x132
> runtime.cgocallbackg(0x7feae6c1d340, 0x7ffcc89baf10, 0x0)
>         <autogenerated>:1 +0x2b
> runtime.cgocallback(0x0, 0x0, 0x0)
>         /mnt/go/src/runtime/asm_amd64.s:1098 +0xcd
> runtime.goexit({})
>         /mnt/go/src/runtime/asm_amd64.s:1709 +0x1

Cc: Keith Randall <khr@golang.org>
Cc: Sean Liao <sean@liao.dev>
Suggested-by: Ian Lance Taylor <iant@golang.org>
GH: #75856

Author: ariel-anieli

src/runtime/cgocall.go

@@ -592,7 +592,6 @@ func cgoCheckPointer(ptr any, arg any) {
 }
 
 const cgoCheckPointerFail = "cgo argument has Go pointer to unpinned Go pointer"
-const cgoResultFail = "cgo result is unpinned Go pointer or points to unpinned Go pointer"
 
 // cgoCheckArg is the real work of cgoCheckPointer. The argument p
 // is either a pointer to the value (of type t), or the value itself,
@@ -786,10 +785,23 @@ func cgoInRange(p unsafe.Pointer, start, end uintptr) bool {
 // exported Go function. It panics if the result is or contains any
 // other pointer into unpinned Go memory.
 func cgoCheckResult(val any) {
+	var callerName string = " "
+
 	if !goexperiment.CgoCheck2 && debug.cgocheck == 0 {
 		return
 	}
 
+	pc, _, _, ok := Caller(1)
+	if ok {
+		function := FuncForPC(pc)
+
+		// Expected format of cgo caller name: _cgoexp_3c910ddb72c4_foo
+		if function != nil {
+			callerName += function.Name()[21:] + " "
+		}
+	}
+
+	cgoResultFail := "result of cgo function" + callerName + "is unpinned Go pointer or points to unpinned Go pointer"
 	ep := efaceOf(&val)
 	t := ep._type
 	cgoCheckArg(t, ep.data, !t.IsDirectIface(), false, cgoResultFail)