runtime: check for findmoduledatap returning nil

The findmoduledatap function will not return nil in ordinary use, but
check for nil to try to avoid crashing when we are already crashing.

Update golang#11783.

Change-Id: If7b1adb51efab13b4c1a37b6f3c9ad22641a0b56
Reviewed-on: https://go-review.googlesource.com/12391
Run-TryBot: Ian Lance Taylor <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>

src/runtime/symtab.go

@@ -223,6 +223,13 @@ func pcvalue(f *_func, off int32, targetpc uintptr, strict bool) int32 {
 		return -1
 	}
 	datap := findmoduledatap(f.entry) // inefficient
+	if datap == nil {
+		if strict && panicking == 0 {
+			print("runtime: no module data for ", hex(f.entry), "\n")
+			throw("no module data")
+		}
+		return -1
+	}
 	p := datap.pclntable[off:]
 	pc := f.entry
 	val := int32(-1)
@@ -266,6 +273,9 @@ func cfuncname(f *_func) *byte {
 		return nil
 	}
 	datap := findmoduledatap(f.entry) // inefficient
+	if datap == nil {
+		return nil
+	}
 	return (*byte)(unsafe.Pointer(&datap.pclntable[f.nameoff]))
 }
 
@@ -275,6 +285,9 @@ func funcname(f *_func) string {
 
 func funcline1(f *_func, targetpc uintptr, strict bool) (file string, line int32) {
 	datap := findmoduledatap(f.entry) // inefficient
+	if datap == nil {
+		return "?", 0
+	}
 	fileno := int(pcvalue(f, f.pcfile, targetpc, strict))
 	line = pcvalue(f, f.pcln, targetpc, strict)
 	if fileno == -1 || line == -1 || fileno >= len(datap.filetab) {