btf: fix writing out signed enums

The formatter currently doesn't do sign conversion when writing
out enum values. This means that negative signed enum values
end up with large unsigned values. Fix this by doing correct
sign conversion.

Signed-off-by: Lorenz Bauer <lmb@isovalent.com>

btf/format.go

@@ -77,7 +77,13 @@ func (gf *GoFormatter) writeTypeDecl(name string, typ Type) error {
 	gf.w.WriteString("; const ( ")
 	for _, ev := range e.Values {
 		id := gf.enumIdentifier(name, ev.Name)
-		fmt.Fprintf(&gf.w, "%s %s = %d; ", id, name, ev.Value)
+		var value any
+		if e.Signed {
+			value = int64(ev.Value)
+		} else {
+			value = ev.Value
+		}
+		fmt.Fprintf(&gf.w, "%s %s = %d; ", id, name, value)
 	}
 	gf.w.WriteString(")")
 

btf/format_test.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"go/format"
+	"math"
 	"strings"
 	"testing"
 )
@@ -22,7 +23,17 @@ func TestGoTypeDeclaration(t *testing.T) {
 		{&Typedef{Name: "frob", Type: &Int{Size: 8}}, "type t uint64"},
 		{&Int{Size: 16}, "type t [16]byte /* uint128 */"},
 		{&Enum{Values: []EnumValue{{"FOO", 32}}, Size: 4}, "type t uint32; const ( tFOO t = 32; )"},
-		{&Enum{Values: []EnumValue{{"BAR", 1}}, Size: 1, Signed: true}, "type t int8; const ( tBAR t = 1; )"},
+		{
+			&Enum{
+				Values: []EnumValue{
+					{"MINUS_ONE", math.MaxUint64},
+					{"MINUS_TWO", math.MaxUint64 - 1},
+				},
+				Size:   1,
+				Signed: true,
+			},
+			"type t int8; const ( tMINUS_ONE t = -1; tMINUS_TWO t = -2; )",
+		},
 		{
 			&Struct{
 				Name: "enum literals",