proc: do not assume abstract origins precede their uses (#2293)

The DWARF standard does not say that a DW_ATTR_abstract_origin can only
reference entries that appear before it, this change fixes BinaryInfo
to comply. See #2284 for an example of this happening.

pkg/dwarf/dwarfbuilder/info.go

@@ -123,10 +123,11 @@ func (b *Builder) TagClose() {
 }
 
 // Attr adds an attribute to the current DIE.
-func (b *Builder) Attr(attr dwarf.Attr, val interface{}) {
+func (b *Builder) Attr(attr dwarf.Attr, val interface{}) dwarf.Offset {
 	if len(b.tagStack) < 0 {
 		panic("Attr with no open tags")
 	}
+	off := dwarf.Offset(b.info.Len())
 	tag := b.tagStack[len(b.tagStack)-1]
 	if tag.children {
 		panic("Can't add attributes after adding children")
@@ -179,6 +180,16 @@ func (b *Builder) Attr(attr dwarf.Attr, val interface{}) {
 	default:
 		panic("unknown value type")
 	}
+
+	return off
+}
+
+// PatchOffset writes the offset 'patch' at offset patchedOffset.
+func (b *Builder) PatchOffset(patchedOffset, patch dwarf.Offset) {
+	infoBytes := b.info.Bytes()
+	buf := new(bytes.Buffer)
+	binary.Write(buf, binary.LittleEndian, patch)
+	copy(infoBytes[patchedOffset:], buf.Bytes())
 }
 
 func sameTagDescr(a, b tagDescr) bool {

pkg/proc/bininfo.go

@@ -1787,18 +1787,15 @@ func (bi *BinaryInfo) addAbstractSubprogram(entry *dwarf.Entry, ctxt *loadDebugI
 		return
 	}
 
-	fn := Function{
-		Name:   name,
-		offset: entry.Offset,
-		cu:     cu,
-	}
-
 	if entry.Children {
 		bi.loadDebugInfoMapsInlinedCalls(ctxt, reader, cu)
 	}
 
-	bi.Functions = append(bi.Functions, fn)
-	ctxt.abstractOriginTable[entry.Offset] = len(bi.Functions) - 1
+	originIdx := ctxt.lookupAbstractOrigin(bi, entry.Offset)
+	fn := &bi.Functions[originIdx]
+	fn.Name = name
+	fn.offset = entry.Offset
+	fn.cu = cu
 }
 
 // addConcreteInlinedSubprogram adds the concrete entry of a subprogram that was also inlined.
@@ -1812,15 +1809,7 @@ func (bi *BinaryInfo) addConcreteInlinedSubprogram(entry *dwarf.Entry, originOff
 		return
 	}
 
-	originIdx, ok := ctxt.abstractOriginTable[originOffset]
-	if !ok {
-		bi.logger.Warnf("reading debug_info: could not find abstract origin of concrete inlined subprogram at %#x (origin offset %#x)", entry.Offset, originOffset)
-		if entry.Children {
-			reader.SkipChildren()
-		}
-		return
-	}
-
+	originIdx := ctxt.lookupAbstractOrigin(bi, originOffset)
 	fn := &bi.Functions[originIdx]
 	fn.offset = entry.Offset
 	fn.Entry = lowpc
@@ -1905,12 +1894,7 @@ func (bi *BinaryInfo) loadDebugInfoMapsInlinedCalls(ctxt *loadDebugInfoMapsConte
 				continue
 			}
 
-			originIdx, ok := ctxt.abstractOriginTable[originOffset]
-			if !ok {
-				bi.logger.Warnf("reading debug_info: could not find abstract origin (%#x) of inlined call at %#x", originOffset, entry.Offset)
-				reader.SkipChildren()
-				continue
-			}
+			originIdx := ctxt.lookupAbstractOrigin(bi, originOffset)
 			fn := &bi.Functions[originIdx]
 
 			lowpc, highpc, ok := subprogramEntryRange(entry, cu.image)

pkg/proc/dwarf_expr_test.go

@@ -353,3 +353,43 @@ func TestNestedCompileUnts(t *testing.T) {
 		t.Errorf("expected 2 variables, got %d", n)
 	}
 }
+
+func TestAbstractOriginDefinedAfterUse(t *testing.T) {
+	// Tests that an abstract origin entry can appear after its uses.
+	dwb := dwarfbuilder.New()
+	dwb.AddCompileUnit("main", 0x0)
+
+	// Concrete implementation
+	dwb.TagOpen(dwarf.TagSubprogram, "")
+	originRef1 := dwb.Attr(dwarf.AttrAbstractOrigin, dwarf.Offset(0))
+	dwb.Attr(dwarf.AttrLowpc, dwarfbuilder.Address(0x40100))
+	dwb.Attr(dwarf.AttrHighpc, dwarfbuilder.Address(0x41000))
+	dwb.TagClose()
+
+	// Inlined call
+	dwb.AddSubprogram("callingFn", 0x41100, 0x42000)
+	dwb.TagOpen(dwarf.TagInlinedSubroutine, "")
+	originRef2 := dwb.Attr(dwarf.AttrAbstractOrigin, dwarf.Offset(0))
+	dwb.Attr(dwarf.AttrLowpc, dwarfbuilder.Address(0x41150))
+	dwb.Attr(dwarf.AttrHighpc, dwarfbuilder.Address(0x41155))
+	dwb.Attr(dwarf.AttrCallFile, uint8(1))
+	dwb.Attr(dwarf.AttrCallLine, uint8(1))
+	dwb.TagClose()
+	dwb.TagClose()
+
+	// Abstract origin
+	abstractOriginOff := dwb.TagOpen(dwarf.TagSubprogram, "inlinedFn")
+	dwb.Attr(dwarf.AttrInline, uint8(1))
+	dwb.TagClose()
+
+	dwb.TagClose()
+
+	dwb.PatchOffset(originRef1, abstractOriginOff)
+	dwb.PatchOffset(originRef2, abstractOriginOff)
+
+	bi, _ := fakeBinaryInfo(t, dwb)
+	fn := bi.PCToFunc(0x40100)
+	if fn == nil {
+		t.Fatalf("could not find concrete instance of inlined function")
+	}
+}

pkg/proc/types.go

@@ -98,6 +98,16 @@ func newLoadDebugInfoMapsContext(bi *BinaryInfo, image *Image, offsetToVersion m
 	return ctxt
 }
 
+func (ctxt *loadDebugInfoMapsContext) lookupAbstractOrigin(bi *BinaryInfo, off dwarf.Offset) int {
+	r, ok := ctxt.abstractOriginTable[off]
+	if !ok {
+		bi.Functions = append(bi.Functions, Function{})
+		r = len(bi.Functions) - 1
+		ctxt.abstractOriginTable[off] = r
+	}
+	return r
+}
+
 // runtimeTypeToDIE returns the DIE corresponding to the runtime._type.
 // This is done in three different ways depending on the version of go.
 // * Before go1.7 the type name is retrieved directly from the runtime._type