debug/dwarf: better handling for DW_FORM_indirect

Fix a buglet in abbrev processing related to DW_FORM_indirect. When
reading an abbrev entry if we encounter an attribute with form
DW_FORM_indirect, leave the class as ClassUnknown, then when the
abbrev is walked during the reading of the DIE fill in the class based
on the value read at that point (code for handling DW_FORM_indirect
seems to be already partially in place in the DIE reader).

Updates #33488.

Change-Id: I9dc89abf5cc8d7ea96824c0011bef979de0540bf
Reviewed-on: https://go-review.googlesource.com/c/go/+/190158
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

src/debug/dwarf/entry.go

@@ -160,6 +160,9 @@ func formToClass(form format, attr Attr, vers int, b *buf) Class {
 		b.error("cannot determine class of unknown attribute form")
 		return 0
 
+	case formIndirect:
+		return ClassUnknown
+
 	case formAddr, formAddrx, formAddrx1, formAddrx2, formAddrx3, formAddrx4:
 		return ClassAddress
 
@@ -402,7 +405,7 @@ type Offset uint32
 
 // Entry reads a single entry from buf, decoding
 // according to the given abbreviation table.
-func (b *buf) entry(cu *Entry, atab abbrevTable, ubase Offset) *Entry {
+func (b *buf) entry(cu *Entry, atab abbrevTable, ubase Offset, vers int) *Entry {
 	off := b.off
 	id := uint32(b.uint())
 	if id == 0 {
@@ -425,6 +428,7 @@ func (b *buf) entry(cu *Entry, atab abbrevTable, ubase Offset) *Entry {
 		fmt := a.field[i].fmt
 		if fmt == formIndirect {
 			fmt = format(b.uint())
+			e.Field[i].Class = formToClass(fmt, a.field[i].attr, vers, b)
 		}
 		var val interface{}
 		switch fmt {
@@ -784,7 +788,7 @@ func (r *Reader) Next() (*Entry, error) {
 		return nil, nil
 	}
 	u := &r.d.unit[r.unit]
-	e := r.b.entry(r.cu, u.atable, u.base)
+	e := r.b.entry(r.cu, u.atable, u.base, u.vers)
 	if r.b.err != nil {
 		r.err = r.b.err
 		return nil, r.err
@@ -929,7 +933,7 @@ func (d *Data) Ranges(e *Entry) ([][2]uint64, error) {
 			}
 			u := &d.unit[i]
 			b := makeBuf(d, u, "info", u.off, u.data)
-			cu = b.entry(nil, u.atable, u.base)
+			cu = b.entry(nil, u.atable, u.base, u.vers)
 			if b.err != nil {
 				return nil, b.err
 			}

src/debug/dwarf/typeunit.go

@@ -137,7 +137,7 @@ func (tur *typeUnitReader) Next() (*Entry, error) {
 	if len(tur.tu.data) == 0 {
 		return nil, nil
 	}
-	e := tur.b.entry(nil, tur.tu.atable, tur.tu.base)
+	e := tur.b.entry(nil, tur.tu.atable, tur.tu.base, tur.tu.vers)
 	if tur.b.err != nil {
 		tur.err = tur.b.err
 		return nil, tur.err