[Spice-devel] [PATCH spice-protocol v2] qxl_dev: Align QXLRam to 4 bytes

[Frediano Ziglio]

This avoids compilers detect misaligned access which can lead to
warnings.
In QEMU the structure is allocated at the beginning of a 4Kb page,
in Xspice is allocated with a calloc, so the structure will end up 4
bytes aligned as well with these users. We are not aware of other users
of QXLRam, but if there was, it's likely the struct would be at least
naturally aligned, so this change should not impact anyone.
Aligning to 4 bytes maintains the size of the structure unchanged
avoiding possible ABI changes.
clang currently generates an invalid function call if a misaligned
4 byte atomic operation is detected.

This fixes https://bugzilla.redhat.com/show_bug.cgi?id=1565766

Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
---
 spice/end-packed.h   | 1 +
 spice/qxl_dev.h      | 2 +-
 spice/start-packed.h | 2 ++
 3 files changed, 4 insertions(+), 1 deletion(-)

Changes since v1:
- improve commit message.

diff --git a/spice/end-packed.h b/spice/end-packed.h
index 1acea18..0efd588 100644
--- a/spice/end-packed.h
+++ b/spice/end-packed.h
@@ -32,6 +32,7 @@
 /* See start-packed.h for details */
 
 #undef SPICE_ATTR_PACKED
+#undef SPICE_ATTR_ALIGNED
 
 #if defined(__MINGW32__) || !defined(__GNUC__)
 #pragma pack(pop)
diff --git a/spice/qxl_dev.h b/spice/qxl_dev.h
index 9e753c4..a9cc4f4 100644
--- a/spice/qxl_dev.h
+++ b/spice/qxl_dev.h
@@ -253,7 +253,7 @@ SPICE_RING_DECLARE(QXLReleaseRing, uint64_t, QXL_RELEASE_RING_SIZE);
 #define QXL_INTERRUPT_CLIENT_MONITORS_CONFIG  (1 << 5)
 
 /* qxl-1 compat: append only */
-typedef struct SPICE_ATTR_PACKED QXLRam {
+typedef struct SPICE_ATTR_ALIGNED(4) SPICE_ATTR_PACKED QXLRam {
     uint32_t magic;
     uint32_t int_pending;
     uint32_t int_mask;
diff --git a/spice/start-packed.h b/spice/start-packed.h
index ab3fa98..de0c595 100644
--- a/spice/start-packed.h
+++ b/spice/start-packed.h
@@ -48,6 +48,7 @@
 #ifdef __GNUC__
 
 #define SPICE_ATTR_PACKED __attribute__ ((__packed__))
+#define SPICE_ATTR_ALIGNED(n) __attribute__ ((__aligned__ (n)))
 
 #ifdef __MINGW32__
 #pragma pack(push,1)
@@ -58,6 +59,7 @@
 #pragma pack(push)
 #pragma pack(1)
 #define SPICE_ATTR_PACKED
+#define SPICE_ATTR_ALIGNED(n) __declspec (align (n))
 #pragma warning(disable:4200)
 #pragma warning(disable:4103)
 
-- 
2.17.1