Hi,On Wed, Mar 08, 2017 at 07:21:15PM +0100, Christophe de Dinechin wrote:I have several errors like this:
spice-channel.c:1923:12: error: cast from 'uint8_t *' (aka 'unsigned char *') to
'uint32_t *' (aka 'unsigned int *') increases required alignment from 1 to
4 [-Werror,-Wcast-align]
...(uint32_t *)((uint8_t *)c->peer_msg + GUINT32_FROM_LE(c->peer_msg->caps_offset));
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Is there any guarantee that the result pointer will be 32-bit aligned?
In other words, is it guaranteed that the c->peer_msg->caps_offset
will be a multiple of 4? I don’t see this written in the spec.
Based on the answer, the correct fix is:
- If aligned, to cast to a uint32_t * in a way that disables the warning
- If misaligned, to replaced *p with a read operation that is safe when mis-aligned (OS dependent I guess)
Yes, we should check case-by-case. I started doing some work around this(nearly one and half year ago already!) but I got stuck on explainingthe rationale for each cast which would avoid the warnings.You can see the comments and suggestions at the time are in thefollowing thread:https://lists.freedesktop.org/archives/spice-devel/2015-August/021535.html
Ach, I see you used SPICE_ALIGNED_CAST and SPICE_UNALIGNED_CAST. I used SPICE_REALIGN_CAST :-(
Will try to integrate your patches, thanks.
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