dwarf: ensure Goroutine-safety in DWARFLines.Line function (#911)

Signed-off-by: Takeshi Yoneda <takeshi@tetrate.io>

internal/wasmdebug/dwarf.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"sort"
+	"sync"
 )
 
 // DWARFLines is used to retrieve source code line information from the DWARF data.
@@ -15,6 +16,7 @@ type DWARFLines struct {
 	// linesPerEntry maps dwarf.Offset for dwarf.Entry to the list of lines contained by the entry.
 	// The value is sorted in the increasing order by the address.
 	linesPerEntry map[dwarf.Offset][]line
+	mux           sync.Mutex
 }
 
 type line struct {
@@ -37,6 +39,12 @@ func (d *DWARFLines) Line(instructionOffset uint64) string {
 		return ""
 	}
 
+	// DWARFLines is created per Wasm binary, so there's a possibility that multiple instances
+	// created from a same binary face runtime error at the same time, and that results in
+	// concurrent access to this function.
+	d.mux.Lock()
+	defer d.mux.Unlock()
+
 	r := d.d.Reader()
 
 	// Get the dwarf.Entry containing the instruction.

internal/wasmdebug/dwarf_test.go

@@ -3,6 +3,7 @@ package wasmdebug_test
 import (
 	"fmt"
 	"math"
+	"sync"
 	"testing"
 
 	"github.com/tetratelabs/wazero/api"
@@ -44,8 +45,19 @@ func TestDWARFLines_Line_TinyGO(t *testing.T) {
 
 	for _, tc := range tests {
 		t.Run(tc.exp, func(t *testing.T) {
-			actual := mod.DWARFLines.Line(tc.offset)
-			require.Contains(t, actual, tc.exp)
+			// Ensures that DWARFLines.Line is goroutine-safe.
+			const concurrent = 100
+			var wg sync.WaitGroup
+			wg.Add(concurrent)
+
+			for i := 0; i < concurrent; i++ {
+				go func() {
+					defer wg.Done()
+					actual := mod.DWARFLines.Line(tc.offset)
+					require.Contains(t, actual, tc.exp)
+				}()
+			}
+			wg.Wait()
 		})
 	}
 }