From 436fed8ec49a19f2f0cfd84dbbd54464588f4969 Mon Sep 17 00:00:00 2001
From: Frederic Branczyk <fbranczyk@gmail.com>
Date: Tue, 31 Jan 2023 17:40:19 +0100
Subject: [PATCH] godwarf: Allow extracting a DWARF entry's field (#3258)

Previously it was only possible to extract a value of type `any` using
an attribute name. This poses challenges when fields are allowed to have
different classes, and it is ambiguous how to handle them.
---
 pkg/dwarf/godwarf/tree.go | 12 ++++++++++--
 pkg/proc/fncall.go        | 20 ++++++++++++++------
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/pkg/dwarf/godwarf/tree.go b/pkg/dwarf/godwarf/tree.go
index 379da1a9..b9be92ba 100644
--- a/pkg/dwarf/godwarf/tree.go
+++ b/pkg/dwarf/godwarf/tree.go
@@ -11,14 +11,22 @@ import (
 // entry specified by DW_AT_abstract_origin will be searched recursively.
 type Entry interface {
 	Val(dwarf.Attr) interface{}
+	AttrField(dwarf.Attr) *dwarf.Field
 }
 
 type compositeEntry []*dwarf.Entry
 
 func (ce compositeEntry) Val(attr dwarf.Attr) interface{} {
+	if f := ce.AttrField(attr); f != nil {
+		return f.Val
+	}
+	return nil
+}
+
+func (ce compositeEntry) AttrField(a dwarf.Attr) *dwarf.Field {
 	for _, e := range ce {
-		if r := e.Val(attr); r != nil {
-			return r
+		if f := e.AttrField(a); f != nil {
+			return f
 		}
 	}
 	return nil
diff --git a/pkg/proc/fncall.go b/pkg/proc/fncall.go
index 5f378a00..31a0332b 100644
--- a/pkg/proc/fncall.go
+++ b/pkg/proc/fncall.go
@@ -1248,9 +1248,17 @@ func debugCallProtocolReg(archName string, version int) (uint64, bool) {
 	}
 }
 
-type fakeEntry map[dwarf.Attr]interface{}
+type fakeEntry map[dwarf.Attr]*dwarf.Field
 
 func (e fakeEntry) Val(attr dwarf.Attr) interface{} {
+	if e[attr] == nil {
+		return nil
+	}
+
+	return e[attr].Val
+}
+
+func (e fakeEntry) AttrField(attr dwarf.Attr) *dwarf.Field {
 	return e[attr]
 }
 
@@ -1273,11 +1281,11 @@ func regabiMallocgcWorkaround(bi *BinaryInfo) ([]*godwarf.Tree, error) {
 		if err1 != nil {
 			return nil
 		}
-		var e fakeEntry = map[dwarf.Attr]interface{}{
-			dwarf.AttrName:     name,
-			dwarf.AttrType:     typ.Common().Offset,
-			dwarf.AttrLocation: []byte{byte(op.DW_OP_reg0) + byte(reg)},
-			dwarf.AttrVarParam: isret,
+		var e fakeEntry = map[dwarf.Attr]*dwarf.Field{
+			dwarf.AttrName:     &dwarf.Field{Attr: dwarf.AttrName, Val: name, Class: dwarf.ClassString},
+			dwarf.AttrType:     &dwarf.Field{Attr: dwarf.AttrType, Val: typ.Common().Offset, Class: dwarf.ClassReference},
+			dwarf.AttrLocation: &dwarf.Field{Attr: dwarf.AttrLocation, Val: []byte{byte(op.DW_OP_reg0) + byte(reg)}, Class: dwarf.ClassBlock},
+			dwarf.AttrVarParam: &dwarf.Field{Attr: dwarf.AttrVarParam, Val: isret, Class: dwarf.ClassFlag},
 		}
 
 		return &godwarf.Tree{