From 74371554461a5f8cc42e4828d6123febc88c1dec Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Thu, 4 Jul 2019 21:06:17 +0000
Subject: [PATCH] Decrease alignment requirements to 4

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 .clang-format |  1 +
 README.md     | 19 +++++++------------
 wintun.c      |  5 +++--
 3 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/.clang-format b/.clang-format
index 9bbe60a..0b702a7 100644
--- a/.clang-format
+++ b/.clang-format
@@ -98,6 +98,7 @@ StatementMacros: [
     '__drv_preferredFunction',
     '__drv_allocatesMem',
     '__drv_freesMem',
+	'_Field_size_bytes_',
     ]
 TabWidth: '4'
 UseTab: Never
diff --git a/README.md b/README.md
index 3a01a0d..3b31880 100644
--- a/README.md
+++ b/README.md
@@ -89,11 +89,6 @@ After loading the driver and creating a network interface the typical way using
 |   4 bytes, native endian     |
 +------------------------------+
 |                              |
-| padding                      |
-|   12 bytes, all zero         |
-|                              |
-+------------------------------+
-|                              |
 | packet_0                     |
 |   size_0 bytes               |
 |                              |
@@ -101,22 +96,22 @@ After loading the driver and creating a network interface the typical way using
 |                              |
 +------------------------------+
 | padding                      |
-|   16-(size_0&15) bytes,      |
-|   all zero                   |
+|   4-(size_0&3) bytes         |
 +------------------------------+
 | size_1                       |
 |   4 bytes, native endian     |
 +------------------------------+
 |                              |
-| padding                      |
-|   12 bytes, all zero         |
-|                              |
-+------------------------------+
-|                              |
 | packet_1                     |
 |   size_1 bytes               |
 |                              |
 ~                              ~
+|                              |
++------------------------------+
+| padding                      |
+|   4-(size_1&3) bytes         |
++------------------------------+
+~                              ~
 ```
 
 Each packet segment should contain a layer 3 IPv4 or IPv6 packet. Up to 15728640 bytes may be read or written during each call to `ReadFile` or `WriteFile`. All calls to `ReadFile` must be called with the same virtual address, for a given handle. This virtual address must reference pages that are writable for the same length as passed to the first call of `ReadFile`.
diff --git a/wintun.c b/wintun.c
index 3ff9e8c..9ba1b1f 100644
--- a/wintun.c
+++ b/wintun.c
@@ -32,7 +32,7 @@
 #define TUN_EXCH_MAX_PACKETS 256
 /* Maximum exchange packet size - empirically determined by net buffer list (pool) limitations */
 #define TUN_EXCH_MAX_PACKET_SIZE 0xF000
-#define TUN_EXCH_ALIGNMENT 16 /* Memory alignment in exchange buffers */
+#define TUN_EXCH_ALIGNMENT sizeof(ULONG) /* Memory alignment in exchange buffers */
 /* Maximum IP packet size (headers + payload) */
 #define TUN_EXCH_MAX_IP_PACKET_SIZE (TUN_EXCH_MAX_PACKET_SIZE - sizeof(TUN_PACKET))
 /* Maximum size of read/write exchange buffer */
@@ -60,7 +60,8 @@
 typedef struct _TUN_PACKET
 {
     ULONG Size; /* Size of packet data (TUN_EXCH_MAX_IP_PACKET_SIZE max) */
-    _Field_size_bytes_(Size) __declspec(align(TUN_EXCH_ALIGNMENT)) UCHAR Data[]; /* Packet data */
+    _Field_size_bytes_(Size)
+    UCHAR Data[]; /* Packet data */
 } TUN_PACKET;
 
 typedef enum _TUN_FLAGS