From: Christophe de Dinechin <dinechin@xxxxxxxxxx>
For example, something like this:
uint8_t *p8;
uint32_t *p32 = (uint32_t *) p8;
generates a warning like this:
spice-channel.c:1350:10: error: cast from 'uint8_t *' (aka 'unsigned char *') to
'uint32_t *' (aka 'unsigned int *') increases required alignment from 1 to
4 [-Werror,-Wcast-align]
The warning indicates that we end up with a pointer to data that
should be 4-byte aligned, but its value may be misaligned. On x86,
this does not make much of a difference, except a relatively minor
performance penalty. However, on platforms such as ARM, misaligned
accesses are emulated by the kernel, and support for them is optional.
So we may end up with a fault.
The intent of the fix here is to make it easy to identify and rework
places where actual mis-alignment occurs. Wherever casts raise the warning,
they are replaced with a macro:
- SPICE_ALIGNED_CAST(type, value) casts value to type, and indicates that
we believe the resulting pointer is aligned. If it is not, a warning will
be issued.
- SPICE_UNALIGNED_CAST(type, value) casts value to type, and indicates that
we believe the resulting pointer is not always aligned
Any code using SPICE_UNALIGNED_CAST may need to be revisited in order
to improve performance, e.g. by using memcpy.
There are normally no warnings for SPICE_UNALIGNED_CAST, but it is possible
to emit debug messages for mis-alignment in SPICE_UNALIGNED_CAST.
Set environment variable SPICE_DEBUG_ALIGNMENT to activate this check.
Signed-off-by: Christophe de Dinechin <dinechin@xxxxxxxxxx>
---
spice-common | 2 +-
src/channel-cursor.c | 6 +++---
src/channel-display-mjpeg.c | 2 +-
src/decode-glz-tmpl.c | 2 +-
src/spice-channel.c | 14 +++++++++-----
5 files changed, 15 insertions(+), 11 deletions(-)
diff --git a/spice-common b/spice-common
index af682b1..1239c82 160000
--- a/spice-common
+++ b/spice-common
@@ -1 +1 @@
-Subproject commit af682b1b06dea55007d9aa7c37cd443e4349e43f
+Subproject commit 1239c82c54dee0244cca262cca0aa21071b23e24
diff --git a/src/channel-cursor.c b/src/channel-cursor.c
index 609243b..50de5ce 100644
--- a/src/channel-cursor.c
+++ b/src/channel-cursor.c
@@ -340,7 +340,7 @@ static display_cursor *set_cursor(SpiceChannel *channel, SpiceCursor *scursor)
memcpy(cursor->data, data, size);
for (i = 0; i < hdr->width * hdr->height; i++) {
pix_mask = get_pix_mask(data, size, i);
- if (pix_mask && *((guint32*)data + i) == 0xffffff) {
+ if (pix_mask && *(SPICE_ALIGNED_CAST(guint32*, data) + i) == 0xffffff) {
cursor->data[i] = get_pix_hack(i, hdr->width);
} else {
cursor->data[i] |= (pix_mask ? 0 : 0xff000000);
@@ -350,7 +350,7 @@ static display_cursor *set_cursor(SpiceChannel *channel, SpiceCursor *scursor)
case SPICE_CURSOR_TYPE_COLOR16:
for (i = 0; i < hdr->width * hdr->height; i++) {
pix_mask = get_pix_mask(data, size, i);
- pix = *((guint16*)data + i);
+ pix = *(SPICE_ALIGNED_CAST(guint16*,data) + i);
if (pix_mask && pix == 0x7fff) {
cursor->data[i] = get_pix_hack(i, hdr->width);
} else {
@@ -364,7 +364,7 @@ static display_cursor *set_cursor(SpiceChannel *channel, SpiceCursor *scursor)
for (i = 0; i < hdr->width * hdr->height; i++) {
pix_mask = get_pix_mask(data, size + (sizeof(uint32_t) << 4), i);
int idx = (i & 1) ? (data[i >> 1] & 0x0f) : ((data[i >> 1] & 0xf0) >> 4);
- pix = *((uint32_t*)(data + size) + idx);
+ pix = *(SPICE_UNALIGNED_CAST(uint32_t*,(data + size)) + idx);
if (pix_mask && pix == 0xffffff) {
cursor->data[i] = get_pix_hack(i, hdr->width);
} else {
diff --git a/src/channel-display-mjpeg.c b/src/channel-display-mjpeg.c
index 3ae9d21..17c0f4f 100644
--- a/src/channel-display-mjpeg.c
+++ b/src/channel-display-mjpeg.c
@@ -151,7 +151,7 @@ static gboolean mjpeg_decoder_decode_frame(gpointer video_decoder)
#ifndef JCS_EXTENSIONS
{
uint8_t *s = lines[0];
- uint32_t *d = (uint32_t *)s;
+ uint32_t *d = SPICE_ALIGNED_CAST(uint32_t *,s);
if (back_compat) {
for (unsigned int j = lines_read * width; j > 0; ) {
diff --git a/src/decode-glz-tmpl.c b/src/decode-glz-tmpl.c
index b337a8b..7695a28 100644
--- a/src/decode-glz-tmpl.c
+++ b/src/decode-glz-tmpl.c
@@ -178,7 +178,7 @@ static size_t FNAME(decode)(SpiceGlzDecoderWindow *window,
uint64_t image_id, SpicePalette *plt)
{
uint8_t *ip = in_buf;
- OUT_PIXEL *out_pix_buf = (OUT_PIXEL *)out_buf;
+ OUT_PIXEL *out_pix_buf = SPICE_ALIGNED_CAST(OUT_PIXEL *,out_buf);
OUT_PIXEL *op = out_pix_buf;
OUT_PIXEL *op_limit = out_pix_buf + size;
diff --git a/src/spice-channel.c b/src/spice-channel.c
index 3b6231e..88d0567 100644
--- a/src/spice-channel.c
+++ b/src/spice-channel.c
@@ -1312,6 +1312,7 @@ static void spice_channel_send_link(SpiceChannel *channel)
{
SpiceChannelPrivate *c = channel->priv;
uint8_t *buffer, *p;
+ uint32_t *p32;
int protocol, i;
c->link_hdr.magic = SPICE_MAGIC;
@@ -1356,14 +1357,15 @@ static void spice_channel_send_link(SpiceChannel *channel)
memcpy(p, &c->link_hdr, sizeof(c->link_hdr)); p += sizeof(c->link_hdr);
memcpy(p, &c->link_msg, sizeof(c->link_msg)); p += sizeof(c->link_msg);
+ // Need this to avoid error with -Wcast-align
+ p32 = SPICE_UNALIGNED_CAST(uint32_t *,p);
for (i = 0; i < c->common_caps->len; i++) {
- *(uint32_t *)p = GUINT32_TO_LE(g_array_index(c->common_caps, uint32_t, i));
- p += sizeof(uint32_t);
+ *p32++ = GUINT32_TO_LE(g_array_index(c->common_caps, uint32_t, i));
}
for (i = 0; i < c->caps->len; i++) {
- *(uint32_t *)p = GUINT32_TO_LE(g_array_index(c->caps, uint32_t, i));
- p += sizeof(uint32_t);
+ *p32++ = GUINT32_TO_LE(g_array_index(c->caps, uint32_t, i));
}
+ p = (uint8_t *) p32;
CHANNEL_DEBUG(channel, "channel type %d id %d num common caps %u num caps %u",
c->channel_type,
c->channel_id,
@@ -1887,6 +1889,7 @@ static gboolean spice_channel_recv_link_msg(SpiceChannel *channel)
SpiceChannelPrivate *c;
int rc, num_caps, i;
uint32_t *caps, num_channel_caps, num_common_caps;
+ uint8_t *caps_src;
SpiceChannelEvent event = SPICE_CHANNEL_ERROR_LINK;
g_return_val_if_fail(channel != NULL, FALSE);
@@ -1926,7 +1929,8 @@ static gboolean spice_channel_recv_link_msg(SpiceChannel *channel)
/* see original spice/client code: */
/* g_return_if_fail(c->peer_msg + c->peer_msg->caps_offset * sizeof(uint32_t) > c->peer_msg + c->peer_hdr.size); */
- caps = (uint32_t *)((uint8_t *)c->peer_msg + GUINT32_FROM_LE(c->peer_msg->caps_offset));
+ caps_src = (uint8_t *)c->peer_msg + GUINT32_FROM_LE(c->peer_msg->caps_offset);
+ caps = SPICE_UNALIGNED_CAST(uint32_t *, caps_src);
g_array_set_size(c->remote_common_caps, num_common_caps);
for (i = 0; i < num_common_caps; i++, caps++) {
--
2.11.0 (Apple Git-81)
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