diff --git a/build.bat b/build.bat
index edca8de..b7cec37 100644
--- a/build.bat
+++ b/build.bat
@@ -3,7 +3,7 @@ call ../misc/compile_setup.bat
 
 mkdir build
 cd build
-cl -Fe:bld.exe ../code/build_main.cpp -WX -W3 -wd4200 -diagnostics:column -nologo -Zi -D_CRT_SECURE_NO_WARNINGS /MD
+cl -Fe:bld.exe ../code/build_main.cpp -WX -W3 -wd4200 -diagnostics:column -nologo -Zi -D_CRT_SECURE_NO_WARNINGS /fsanitize=address
 cd ..
 build\bld.exe
 
diff --git a/build.sh b/build.sh
index 649d62c..a9f57a4 100644
--- a/build.sh
+++ b/build.sh
@@ -1,3 +1,3 @@
 #!/usr/bin/env bash
-gcc -o bld code/build_main.cpp -g 
-./bld
+gcc -o bld code/build_main.cpp -g
+./bld cc=clang
diff --git a/build_file.cpp b/build_file.cpp
index 0b908ea..e53b810 100644
--- a/build_file.cpp
+++ b/build_file.cpp
@@ -1,6 +1,7 @@
 #include "code/build_lib.cpp"
 
-int CompileFiles(Strs cc, Strs files);
+void CompileFiles(Strs cc, Strs files);
+int ReturnValue = 0;
 
 int Main() {
     Strs cc = CMDLine.get("cc"_s, ON_WINDOWS("cl"_s) ON_MAC("clang"_s) ON_LINUX("gcc"_s));
@@ -12,10 +13,10 @@ int Main() {
         }
     }
 
-    return 0;
+    return ReturnValue;
 }
 
-int CompileFiles(Strs cc, Strs files) {
+void CompileFiles(Strs cc, Strs files) {
     int result = 0;
     Str exe = FilenameWithoutExt(files[0]);
     Str filestr = Merge(files);
@@ -28,6 +29,11 @@ int CompileFiles(Strs cc, Strs files) {
     else {
         result = OS_SystemF("cl -Fe:%Q.exe %Q -Zi -WX -W3 -wd4200 -diagnostics:column -nologo -D_CRT_SECURE_NO_WARNINGS -fsanitize=address -RTC1", exe, filestr);
     }
-    if (result == 0) result = OS_SystemF(IF_WINDOWS_ELSE("", "./") "%Q.exe", exe);
-    return result;
+
+    if (result == 0) {
+        result = OS_SystemF(IF_WINDOWS_ELSE("", "./") "%Q.exe", exe);
+    }
+    else {
+        ReturnValue = result;
+    }
 }
diff --git a/code/arena.c b/code/arena.c
index 13d2b86..c787712 100644
--- a/code/arena.c
+++ b/code/arena.c
@@ -33,38 +33,11 @@ MA_API void MA_MemoryCopy(void *dst, void *src, size_t size) {
     #endif
 #endif
 
-// Marks memory region [addr, addr+size) as unaddressable.
-// This memory must be previously allocated by the user program. Accessing
-// addresses in this region from instrumented code is forbidden until
-// this region is unpoisoned. This function is not guaranteed to poison
-// the whole region - it may poison only subregion of [addr, addr+size) due
-// to ASan alignment restrictions.
-// Method is NOT thread-safe in the sense that no two threads can
-// (un)poison memory in the same memory region simultaneously.
-void __asan_poison_memory_region(void const volatile *addr, size_t size);
-// Marks memory region [addr, addr+size) as addressable.
-// This memory must be previously allocated by the user program. Accessing
-// addresses in this region is allowed until this region is poisoned again.
-// This function may unpoison a superregion of [addr, addr+size) due to
-// ASan alignment restrictions.
-// Method is NOT thread-safe in the sense that no two threads can
-// (un)poison memory in the same memory region simultaneously.
-void __asan_unpoison_memory_region(void const volatile *addr, size_t size);
-
-// User code should use macros instead of functions.
-#if defined(__clang__)
-    #if defined(__SANITIZE_ADDRESS__) || __has_feature(address_sanitizer)
-        #define ASAN_POISON_MEMORY_REGION(addr, size) \
-            __asan_poison_memory_region((addr), (size))
-        #define ASAN_UNPOISON_MEMORY_REGION(addr, size) \
-            __asan_unpoison_memory_region((addr), (size))
-    #endif
-#endif
-#ifndef ASAN_POISON_MEMORY_REGION
-    #define ASAN_POISON_MEMORY_REGION(addr, size) \
-        ((void)(addr), (void)(size))
-    #define ASAN_UNPOISON_MEMORY_REGION(addr, size) \
-        ((void)(addr), (void)(size))
+#if defined(__SANITIZE_ADDRESS__)
+    #include <sanitizer/asan_interface.h>
+#else
+    #define ASAN_POISON_MEMORY_REGION(addr, size) ((void)(addr), (void)(size))
+    #define ASAN_UNPOISON_MEMORY_REGION(addr, size) ((void)(addr), (void)(size))
 #endif
 
 MA_API size_t MA_GetAlignOffset(size_t size, size_t align) {
@@ -107,7 +80,7 @@ MA_API void MA_PopToPos(MA_Arena *arena, size_t pos) {
     pos = MA_CLAMP(pos, arena->base_len, arena->len);
     size_t size = arena->len - pos;
     arena->len = pos;
-    ASAN_POISON_MEMORY_REGION(arena->memory.data + pos, size);
+    ASAN_POISON_MEMORY_REGION(arena->memory.data + arena->len, size);
 }
 
 MA_API void MA_PopSize(MA_Arena *arena, size_t size) {
@@ -158,7 +131,7 @@ MA_API void *MA_PushSizeNonZeroed(MA_Arena *a, size_t size) {
     uint8_t *result = a->memory.data + aligned_len;
     a->len += size_with_alignment;
     MA_ASSERT(a->len <= a->memory.commit);
-    ASAN_UNPOISON_MEMORY_REGION(result, a->len);
+    ASAN_UNPOISON_MEMORY_REGION(result, size);
     return (void *)result;
 }
 
@@ -205,6 +178,7 @@ MA_API void MA_InitFromBuffer(MA_Arena *arena, void *buffer, size_t size) {
     arena->memory.commit = size;
     arena->memory.reserve = size;
     arena->alignment = MA_DEFAULT_ALIGNMENT;
+    ASAN_POISON_MEMORY_REGION(arena->memory.data, arena->memory.reserve);
 }
 
 MA_API MA_Arena MA_MakeFromBuffer(void *buffer, size_t size) {
diff --git a/code/filesystem.c b/code/filesystem.c
index 4e9b454..a226560 100644
--- a/code/filesystem.c
+++ b/code/filesystem.c
@@ -171,11 +171,11 @@ OS_API S8_List OS_ListDir(MA_Arena *arena, S8_String path, unsigned flags) {
             S8_String filename = UTF_CreateStringFromWidechar(scratch.arena, ffd.cFileName, S8_WideLength(ffd.cFileName));
             S8_String rel_abs_path = S8_Format(scratch.arena, "%Q/%Q%Q", it->string, filename, dir ? S8_Lit("/") : S8_Lit(""));
             if (flags & OS_RELATIVE_PATHS) {
-                S8_AddNode(arena, &result, rel_abs_path);
+                S8_Add(arena, &result, rel_abs_path);
             }
             else {
                 S8_String abs_path = OS_GetAbsolutePath(arena, rel_abs_path);
-                S8_AddNode(arena, &result, abs_path);
+                S8_Add(arena, &result, abs_path);
             }
 
             if (dir && flags & OS_RECURSIVE) {
diff --git a/code/io.c b/code/io.c
index ff8e4f5..eddbb64 100644
--- a/code/io.c
+++ b/code/io.c
@@ -58,15 +58,15 @@ IO_API bool IO__FatalErrorf(const char *file, int line, const char *msg, ...) {
         char buff2[2048];
         char *result = buff2;
         char *b = 0;
-        int size = IO_SNPRINTF(buff2, sizeof(buff2), "%s(%d): error: %s \n", file, line, user_message);
-        if (size >= sizeof(buff2)) {
-            size += 4;
-            b = (char *)IO_ALLOCATE(size);
-            size = IO_SNPRINTF(b, size, "%s(%d): error: %s \n", file, line, user_message);
+        int size2 = IO_SNPRINTF(buff2, sizeof(buff2), "%s(%d): error: %s \n", file, line, user_message);
+        if (size2 >= sizeof(buff2)) {
+            size2 += 4;
+            b = (char *)IO_ALLOCATE(size2);
+            size2 = IO_SNPRINTF(b, size2, "%s(%d): error: %s \n", file, line, user_message);
             result = b;
         }
 
-        ret = IO_OutputError(result, size);
+        ret = IO_OutputError(result, size2);
         if (ret == IO_ErrorResult_Exit) {
             IO_Exit(1);
         }
diff --git a/code/stb_sprintf.h b/code/stb_sprintf.h
index 5b626c9..5b91110 100644
--- a/code/stb_sprintf.h
+++ b/code/stb_sprintf.h
@@ -158,6 +158,10 @@ PERFORMANCE vs MSVC 2008 32-/64-bit (GCC is even slower than MSVC):
         #if defined(__SANITIZE_ADDRESS__) && __SANITIZE_ADDRESS__
             #define STBSP__ASAN __attribute__((__no_sanitize_address__))
         #endif
+    #elif defined(_MSC_VER)
+        #ifdef __SANITIZE_ADDRESS__
+            #define STBSP__ASAN __declspec(no_sanitize_address)
+        #endif
     #endif
 
     #ifndef STBSP__ASAN
diff --git a/code/string.c b/code/string.c
index 015696b..fa921f4 100644
--- a/code/string.c
+++ b/code/string.c
@@ -486,6 +486,13 @@ S8_API S8_Node *S8_AddNode(S8_Allocator allocator, S8_List *list, S8_String stri
     return node;
 }
 
+S8_API S8_Node *S8_Add(S8_Allocator allocator, S8_List *list, S8_String string) {
+    S8_String copy = S8_Copy(allocator, string);
+    S8_Node *node = S8_CreateNode(allocator, copy);
+    S8_AddExistingNode(list, node);
+    return node;
+}
+
 S8_API S8_String S8_AddF(S8_Allocator allocator, S8_List *list, const char *str, ...) {
     S8_FORMAT(allocator, str, result);
     S8_AddNode(allocator, list, result);
diff --git a/code/string.h b/code/string.h
index ca3dd3c..1c75c78 100644
--- a/code/string.h
+++ b/code/string.h
@@ -114,4 +114,5 @@ S8_API S8_List S8_MakeList(S8_Allocator allocator, S8_String a);
 S8_API S8_List S8_CopyList(S8_Allocator allocator, S8_List a);
 S8_API S8_List S8_ConcatLists(S8_Allocator allocator, S8_List a, S8_List b);
 S8_API S8_Node *S8_AddNode(S8_Allocator allocator, S8_List *list, S8_String string);
+S8_API S8_Node *S8_Add(S8_Allocator allocator, S8_List *list, S8_String string);
 S8_API S8_String S8_AddF(S8_Allocator allocator, S8_List *list, const char *str, ...);
diff --git a/test/test_arena.cpp b/test/test_arena.cpp
index 8f658f0..ad3c3ff 100644
--- a/test/test_arena.cpp
+++ b/test/test_arena.cpp
@@ -18,6 +18,15 @@ void TestBootstrapArenaClear() {
     for (int i = 0; i < 1024; i += 1) {
         IO_Assert(vals[i] == i);
     }
+
+    size_t len = arena->len;
+    MA_PopSize(arena, 512);
+    IO_Assert(len == arena->len + 512);
+    ((char *)arena->memory.data)[arena->len - 1] = 0;
+
+    MA_PopToPos(arena, 512);
+    IO_Assert(arena->len == 512);
+    ((char *)arena->memory.data)[arena->len - 1] = 0;
 }
 
 void TestScratch() {