sys/targets: change the default DataOffset value

The current default value sometimes intersects with the addresses used
by malloc, which causes executor memory corruptions.

Closes #5674.

sys/targets/targets.go

@@ -702,7 +702,7 @@ func initTarget(target *Target, OS, arch string) {
 		target.NeedSyscallDefine = needSyscallDefine
 	}
 	if target.DataOffset == 0 {
-		target.DataOffset = 512 << 20
+		target.DataOffset = target.defaultDataOffset()
 	}
 	target.NumPages = (16 << 20) / target.PageSize
 	sourceDir := getSourceDir(target)
@@ -774,6 +774,15 @@ func initTarget(target *Target, OS, arch string) {
 	target.initAddr2Line()
 }
 
+func (target *Target) defaultDataOffset() uint64 {
+	if target.PtrSize == 8 {
+		// An address from ASAN's 64-bit HighMem area.
+		return 0x200000000000
+	}
+	// From 32-bit HighMem area.
+	return 0x80000000
+}
+
 func (target *Target) initAddr2Line() {
 	// Initialize addr2line lazily since lots of tests don't need it,
 	// but we invoke a number of external binaries during addr2line detection.