Re: [PATCH 4/7] hw/ide/atapi: Be explicit that assigning to s->lcyl truncates

[Markus Armbruster]

Peter Maydell <peter.maydell@linaro.org> writes:

> In ide_atapi_cmd_reply_end() we calculate a 16-bit size, and then
> assign its two halves to s->lcyl and s->hcyl like this:
>
>            s->lcyl = size;
>            s->hcyl = size >> 8;
>
> Coverity warns that the first line here can overflow the
> 8-bit s->lcyl variable. This is true, and in this case we're
> deliberately only after the low 8 bits of the value. The
> code is clearer to both humans and Coverity if we're explicit
> that we only wanted the low 8 bits, though.
>

Resolves?

> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  hw/ide/atapi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/ide/atapi.c b/hw/ide/atapi.c
> index fcb6cca1573..e82959dc2d3 100644
> --- a/hw/ide/atapi.c
> +++ b/hw/ide/atapi.c
> @@ -265,7 +265,7 @@ void ide_atapi_cmd_reply_end(IDEState *s)
               /* a new transfer is needed */
               s->nsector = (s->nsector & ~7) | ATAPI_INT_REASON_IO;
               ide_bus_set_irq(s->bus);
               byte_count_limit = atapi_byte_count_limit(s);
               trace_ide_atapi_cmd_reply_end_bcl(s, byte_count_limit);
               size = s->packet_transfer_size;
               if (size > byte_count_limit) {
                   /* byte count limit must be even if this case */
                   if (byte_count_limit & 1)
>                      byte_count_limit--;
>                  size = byte_count_limit;
>              }
> -            s->lcyl = size;
> +            s->lcyl = size & 0xff;
>              s->hcyl = size >> 8;
>              s->elementary_transfer_size = size;
>              /* we cannot transmit more than one sector at a time */

@size is int.  I wonder why it's fine with size >> 8...  ah,
atapi_byte_count_limit() returns uint16_t, and Coverity is smart enough
to data-flow this via @byte_count_limit into @size.

Reviewed-by: Markus Armbruster <armbru@redhat.com>