proc: ignore DW_TAG_inlined_subroutine entries without abstract origin (

go-delve#1637)

GCC produces DW_TAG_inlined_subroutine entries without a
DW_AT_abstract_origin attribute.
From the bug report:

 <1><1fe6c7c>: Abbrev Number: 41 (DW_TAG_subprogram)
    <1fe6c7d>   DW_AT_external    : 1
    <1fe6c7d>   DW_AT_name        : (indirect string, offset: 0x485814): MultiGetImpl
    (omissis)
 <2><1fe6c9e>: Abbrev Number: 65 (DW_TAG_inlined_subroutine)
    <1fe6c9f>   DW_AT_low_pc      : 0x311023a
    <1fe6ca7>   DW_AT_high_pc     : 0x5
    <1fe6caf>   DW_AT_call_file   : 10
    <1fe6cb0>   DW_AT_call_line   : 1690
 <2><1fe6cb2>: Abbrev Number: 20 (DW_TAG_inlined_subroutine)
    <1fe6cb3>   DW_AT_abstract_origin: <0x1ffb534>
    <1fe6cb7>   DW_AT_entry_pc    : 0x311023f
    <1fe6cbf>   DW_AT_ranges      : 0xe9bf20
    <1fe6cc3>   DW_AT_call_file   : 10
    <1fe6cc4>   DW_AT_call_line   : 1690

Inlined subroutine at 1fe6c9e doesn't have abstract origin, a name or a
declaration location. It's unclear whether this is in-standard and what
it even means.

Let's ignore it.

Fixes go-delve#1636

pkg/dwarf/dwarfbuilder/info.go

@@ -92,7 +92,9 @@ func (b *Builder) TagOpen(tag dwarf.Tag, name string) dwarf.Offset {
 	ts.tag = tag
 	b.info.WriteByte(0)
 	b.tagStack = append(b.tagStack, ts)
-	b.Attr(dwarf.AttrName, name)
+	if name != "" {
+		b.Attr(dwarf.AttrName, name)
+	}
 
 	return ts.off
 }

pkg/proc/dwarf_expr_test.go

@@ -292,3 +292,18 @@ func TestLocationCovers(t *testing.T) {
 	}
 
 }
+
+func TestIssue1636_InlineWithoutOrigin(t *testing.T) {
+	// Gcc (specifically GNU C++11 6.3.0) will emit DW_TAG_inlined_subroutine
+	// without a DW_AT_abstract_origin or a name. What is an inlined subroutine
+	// without a reference to an abstract origin or even a name? Regardless,
+	// Delve shouldn't crash.
+	dwb := dwarfbuilder.New()
+	dwb.AddCompileUnit("main", 0x0)
+	dwb.AddSubprogram("main.main", 0x40100, 0x41000)
+	dwb.TagOpen(dwarf.TagInlinedSubroutine, "")
+	dwb.TagClose()
+	dwb.TagClose()
+	dwb.TagClose()
+	fakeBinaryInfo(t, dwb)
+}

pkg/proc/types.go

@@ -410,7 +410,7 @@ func (bi *BinaryInfo) loadDebugInfoMapsCompileUnit(ctxt *loadDebugInfoMapsContex
 					if entry.Tag == 0 {
 						break
 					}
-					if entry.Tag == dwarf.TagInlinedSubroutine {
+					if entry.Tag == dwarf.TagInlinedSubroutine && entry.Val(dwarf.AttrAbstractOrigin) != nil {
 						originOffset := entry.Val(dwarf.AttrAbstractOrigin).(dwarf.Offset)
 						name := ctxt.abstractOriginNameTable[originOffset]
 						if ranges, _ := image.dwarf.Ranges(entry); len(ranges) == 1 {