From 4d54c7392f4267262a7a10cf73b7f8fd5f4fa31a Mon Sep 17 00:00:00 2001
From: Shengwen Cheng <shengwen1997.tw@gmail.com>
Date: Wed, 4 Sep 2024 08:16:29 +0800
Subject: [PATCH] Introduce PACKED macro

Introduce PACKED macro for cross-platform structure alignment, frequently used
by VirtIO device implementations in the semu.
---
 common.h     | 9 +++++++++
 virtio-blk.c | 8 ++++----
 virtio-net.c | 4 ++--
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/common.h b/common.h
index 2a45682..5c6d807 100644
--- a/common.h
+++ b/common.h
@@ -25,3 +25,12 @@ static inline int ilog2(int x)
  */
 #define RANGE_CHECK(x, minx, size) \
     ((int32_t) ((x - minx) | (minx + size - 1 - x)) >= 0)
+
+/* Packed macro */
+#if defined(__GNUC__) || defined(__clang__)
+#define PACKED(name) name __attribute__((packed))
+#elif defined(_MSC_VER)
+#define PACKED(name) __pragma(pack(push, 1)) name __pragma(pack(pop))
+#else /* unsupported compilers */
+#define PACKED(name)
+#endif
diff --git a/virtio-blk.c b/virtio-blk.c
index 416583b..63ecf1d 100644
--- a/virtio-blk.c
+++ b/virtio-blk.c
@@ -26,7 +26,7 @@
 
 #define PRIV(x) ((struct virtio_blk_config *) x->priv)
 
-struct virtio_blk_config {
+PACKED(struct virtio_blk_config {
     uint64_t capacity;
     uint32_t size_max;
     uint32_t seg_max;
@@ -55,14 +55,14 @@ struct virtio_blk_config {
     uint32_t max_write_zeroes_seg;
     uint8_t write_zeroes_may_unmap;
     uint8_t unused1[3];
-} __attribute__((packed));
+});
 
-struct vblk_req_header {
+PACKED(struct vblk_req_header {
     uint32_t type;
     uint32_t reserved;
     uint64_t sector;
     uint8_t status;
-} __attribute__((packed));
+});
 
 static struct virtio_blk_config vblk_configs[VBLK_DEV_CNT_MAX];
 static int vblk_dev_cnt = 0;
diff --git a/virtio-net.c b/virtio-net.c
index 69642de..ddba34d 100644
--- a/virtio-net.c
+++ b/virtio-net.c
@@ -30,12 +30,12 @@
 
 enum { VNET_QUEUE_RX = 0, VNET_QUEUE_TX = 1 };
 
-struct virtio_net_config {
+PACKED(struct virtio_net_config {
     uint8_t mac[6];
     uint16_t status;
     uint16_t max_virtqueue_pairs;
     uint16_t mtu;
-} __attribute__((packed));
+});
 
 static struct virtio_net_config vnet_configs[VNET_DEV_CNT_MAX];
 static int vnet_dev_cnt = 0;