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troop_call.go
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/
troop_call.go
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package goof
import (
"debug/dwarf"
"reflect"
"sort"
"unsafe"
"github.com/zeebo/errs"
)
func (t *Troop) addFunctions() error {
reader := t.data.Reader()
for {
entry, err := reader.Next()
if err != nil {
return errs.Wrap(err)
}
if entry == nil {
break
}
if entry.Tag != dwarf.TagSubprogram {
continue
}
name, ok := entry.Val(dwarf.AttrName).(string)
if !ok {
continue
}
pc, ok := entry.Val(dwarf.AttrLowpc).(uint64)
if !ok {
continue
}
dtypes, err := getFunctionArgTypes(t.data, entry)
if err != nil {
continue
}
_, err = t.findDwarfTypes(dtypes)
if err != nil {
continue
}
t.functions[name] = functionCacheEntry{
pc: pc,
dtypes: dtypes,
}
}
return nil
}
func (t *Troop) Functions() ([]string, error) {
if err := t.check(); err != nil {
return nil, err
}
out := make([]string, 0, len(t.functions))
for name := range t.functions {
out = append(out, name)
}
sort.Strings(out)
return out, nil
}
func (t *Troop) Call(name string, args ...interface{}) ([]interface{}, error) {
if err := t.check(); err != nil {
return nil, err
}
// and so it begins. find the function, the pc, and the types of the args
// and return values. we don't know which is which, but we assume the
// caller passed the appropriate things.
entry, ok := t.functions[name]
if !ok {
return nil, errs.New("call %s: unknown or uncallable function", name)
}
pc, dtypes := entry.pc, entry.dtypes
// make sure they didn't pass more arguments than total types
num_results := len(dtypes) - len(args)
if num_results < 0 {
return nil, errs.New("call %s: too many args", name)
}
// build the arguments, checking consistency and doing hacks to make it
// nice to use.
in, in_types, err := t.buildArguments(args, dtypes[:len(args)])
if err != nil {
return nil, errs.New("call %s: %v", name, err)
}
// the rest must be the return values, RIGHT? LOL
out_types, err := t.findDwarfTypes(dtypes[len(args):])
if err != nil {
return nil, errs.New("call %s: %v", name, err)
}
// make it happen
fn_typ := reflect.FuncOf(in_types, out_types, false)
fn := reflect.ValueOf(makeInterface(dataPtr(fn_typ), unsafe.Pointer(&pc)))
return ifaces(fn.Call(in)), nil
}
func (t *Troop) buildArguments(args []interface{}, dtypes []dwarf.Type) (
[]reflect.Value, []reflect.Type, error) {
if len(args) != len(dtypes) {
return nil, nil, errs.New("number of arguments does not match")
}
// so I want the Call signatrue to have args passed as ...interface{}
// because that makes the api nice: taking a reflect.Value is hard for the
// consumer.
//
// Unfortunately, that means that if you pass an interface type in, they
// get down-casted to just interface{}. Doubly unfortunately, the itab
// pointer was lost when the value was converted to an interface{} instead
// of whatever interface it was in the first place.
//
// So let's just look and see if we can find the interface type in the
// types map based on the dwarf type. If not, shoot. Hopefully that's
// rare! Maybe we can expose a CallReflect api that can get around this.
//
// Heh.
in_types := make([]reflect.Type, 0, len(args))
in := make([]reflect.Value, 0, len(args))
for i, arg := range args {
dtyp := dtypes[i]
val, err := t.constructValue(arg, dtyp)
if err != nil {
return nil, nil, errs.New("arg %d: %v", i, err)
}
in_types = append(in_types, val.Type())
in = append(in, val)
}
return in, in_types, nil
}
func (t *Troop) constructValue(arg interface{}, dtyp dwarf.Type) (
val reflect.Value, err error) {
rtyp, err := t.consistentValue(arg, dtyp)
if err != nil {
return val, err
}
if arg == nil {
return reflect.New(rtyp).Elem(), nil
}
return reflect.ValueOf(arg).Convert(rtyp), nil
}
func (t *Troop) consistentValue(arg interface{}, dtyp dwarf.Type) (
reflect.Type, error) {
rtyp, err := t.findDwarfType(dtyp)
if err != nil {
return nil, err
}
if arg == nil {
if !reflectCanBeNil(rtyp) {
return nil, errs.New("passing nil to non-nillable type: %v",
rtyp)
}
return rtyp, nil
}
if !reflect.TypeOf(arg).ConvertibleTo(rtyp) {
return nil, errs.New("cannot convert %v to %T", rtyp, arg)
}
return rtyp, nil
}