From cc75fe4fe5640ad16c64225d809636d391691f46 Mon Sep 17 00:00:00 2001
From: radare <pancake@nopcode.org>
Date: Sat, 21 Mar 2020 12:24:34 +0100
Subject: [PATCH] builtin: Fix undefined behaviour when allocating empty
 structs (#4088)

---
 vlib/builtin/builtin.v            |  3 +++
 vlib/compiler/tests/struct_test.v | 13 +++++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/vlib/builtin/builtin.v b/vlib/builtin/builtin.v
index da37a4f3ae..3d391a7748 100644
--- a/vlib/builtin/builtin.v
+++ b/vlib/builtin/builtin.v
@@ -177,6 +177,9 @@ pub fn free(ptr voidptr) {
 }
 
 pub fn memdup(src voidptr, sz int) voidptr {
+	if sz == 0 {
+		return vcalloc(1)
+	}
 	mem := malloc(sz)
 	return C.memcpy(mem, src, sz)
 }
diff --git a/vlib/compiler/tests/struct_test.v b/vlib/compiler/tests/struct_test.v
index 7769d538f3..5328c3379c 100644
--- a/vlib/compiler/tests/struct_test.v
+++ b/vlib/compiler/tests/struct_test.v
@@ -1,10 +1,10 @@
-struct A{
+struct A {
 mut:
 	val int
 	nums []int
 }
 
-struct B{
+struct B {
 mut:
 	a A
 }
@@ -26,6 +26,9 @@ struct Foo {
 	@type string
 }
 
+struct Empty {
+}
+
 //We need to make sure that this compiles with all the reserved names.
 struct ReservedKeywords {
 	delete   int
@@ -55,6 +58,12 @@ struct ReservedKeywords {
 	while    int
 }
 
+fn test_empty_struct() {
+	d := &Empty{}
+	println(d) // != voidptr(0)
+	println(sizeof(Empty)) // == 0
+}
+
 fn test_struct_levels() {
 	mut c := C{}
 	assert c.nums.len == 0