proc: be more lenient when parsing debug_info (#2394)

- allow a concrete subprogram to be treated as the abstract origin for an inlined call
- allow nameless concrete and abstract subprograms

Fixes #2393

pkg/proc/bininfo.go

@@ -1917,10 +1917,8 @@ func (bi *BinaryInfo) addAbstractSubprogram(entry *dwarf.Entry, ctxt *loadDebugI
 	name, ok := subprogramEntryName(entry, cu)
 	if !ok {
 		bi.logger.Warnf("reading debug_info: abstract subprogram without name at %#x", entry.Offset)
-		if entry.Children {
-			reader.SkipChildren()
-		}
-		return
+		// In some cases clang produces abstract subprograms that do not have a
+		// name, but we should process them anyway.
 	}
 
 	if entry.Children {
@@ -1950,6 +1948,7 @@ func (bi *BinaryInfo) addConcreteInlinedSubprogram(entry *dwarf.Entry, originOff
 	fn.offset = entry.Offset
 	fn.Entry = lowpc
 	fn.End = highpc
+	fn.cu = cu
 
 	if entry.Children {
 		bi.loadDebugInfoMapsInlinedCalls(ctxt, reader, cu)
@@ -1962,29 +1961,25 @@ func (bi *BinaryInfo) addConcreteSubprogram(entry *dwarf.Entry, ctxt *loadDebugI
 	lowpc, highpc, ok := subprogramEntryRange(entry, cu.image)
 	if !ok {
 		bi.logger.Warnf("reading debug_info: concrete subprogram without address range at %#x", entry.Offset)
-		if entry.Children {
-			reader.SkipChildren()
-		}
-		return
+		// When clang inlines a function, in some cases, it produces a concrete
+		// subprogram without address range and then inlined calls that reference
+		// it, instead of producing an abstract subprogram.
+		// It is unclear if this behavior is standard.
 	}
 
 	name, ok := subprogramEntryName(entry, cu)
 	if !ok {
 		bi.logger.Warnf("reading debug_info: concrete subprogram without name at %#x", entry.Offset)
-		if entry.Children {
-			reader.SkipChildren()
-		}
-		return
 	}
 
-	fn := Function{
-		Name:   name,
-		Entry:  lowpc,
-		End:    highpc,
-		offset: entry.Offset,
-		cu:     cu,
-	}
-	bi.Functions = append(bi.Functions, fn)
+	originIdx := ctxt.lookupAbstractOrigin(bi, entry.Offset)
+	fn := &bi.Functions[originIdx]
+
+	fn.Name = name
+	fn.Entry = lowpc
+	fn.End = highpc
+	fn.offset = entry.Offset
+	fn.cu = cu
 
 	if entry.Children {
 		bi.loadDebugInfoMapsInlinedCalls(ctxt, reader, cu)
@@ -2030,9 +2025,6 @@ func (bi *BinaryInfo) loadDebugInfoMapsInlinedCalls(ctxt *loadDebugInfoMapsConte
 				continue
 			}
 
-			originIdx := ctxt.lookupAbstractOrigin(bi, originOffset)
-			fn := &bi.Functions[originIdx]
-
 			lowpc, highpc, ok := subprogramEntryRange(entry, cu.image)
 			if !ok {
 				bi.logger.Warnf("reading debug_info: inlined call without address range at %#x", entry.Offset)
@@ -2054,12 +2046,19 @@ func (bi *BinaryInfo) loadDebugInfoMapsInlinedCalls(ctxt *loadDebugInfoMapsConte
 				continue
 			}
 
+			originIdx := ctxt.lookupAbstractOrigin(bi, originOffset)
+			fn := &bi.Functions[originIdx]
+
 			fn.InlinedCalls = append(fn.InlinedCalls, InlinedCall{
 				cu:     cu,
 				LowPC:  lowpc,
 				HighPC: highpc,
 			})
 
+			if fn.cu == nil {
+				fn.cu = cu
+			}
+
 			fl := fileLine{callfile, int(callline)}
 			bi.inlinedCallLines[fl] = append(bi.inlinedCallLines[fl], lowpc)
 		}

pkg/proc/types.go

@@ -103,6 +103,7 @@ func (ctxt *loadDebugInfoMapsContext) lookupAbstractOrigin(bi *BinaryInfo, off d
 	if !ok {
 		bi.Functions = append(bi.Functions, Function{})
 		r = len(bi.Functions) - 1
+		bi.Functions[r].offset = off
 		ctxt.abstractOriginTable[off] = r
 	}
 	return r