Re: [Qemu-devel] [Qemu-block] [PATCH 0/3] block/qcow*: Don't take address of fields in packed structs

[John Snow <jsnow@redhat.com>]

On 10/09/2018 01:24 PM, Peter Maydell wrote:
> Taking the address of a field in a packed struct is a bad idea, because
> it might not be actually aligned enough for that pointer type (and
> thus cause a crash on dereference on some host architectures). Newer
> versions of clang warn about this. Avoid the bug by not using the
> "modify in place" byte swapping functions.
> 
> There are a few places in the affected files where the in-place swap
> function is used on something other than a packed struct field; we
> convert those anyway, for consistency.
> 
> Patches produced mechanically using spatch; in one case I also
> did a little hand-editing to wrap overlong lines that checkpatch
> would otherwise complain about.
> 
> (clang also complains about other files in block: vdi.c, vpc.c,
> vhdx.h, vhdx.c, vhdx-endian.c, vhdx-log.c -- I may produce patches
> for those later if nobody else gets there first.)
> 
> thanks
> -- PMM
> 
> Peter Maydell (3):
>   block/qcow2: Don't take address of fields in packed structs
>   block/qcow: Don't take address of fields in packed structs
>   block/qcow2-bitmap: Don't take address of fields in packed structs
> 
>  block/qcow.c         | 18 ++++++-------
>  block/qcow2-bitmap.c | 24 ++++++++---------
>  block/qcow2.c        | 64 +++++++++++++++++++++++---------------------
>  3 files changed, 55 insertions(+), 51 deletions(-)
> 

Tested-by: John Snow <jsnow@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>