Re: [PULL 2/2] core/register: Specify instance_size in the TypeInfo

[Peter Maydell]

On Sun, 27 Sep 2020 at 15:00, Alistair Francis <alistair.francis@wdc.com> wrote:
>
> Reported-by: Eduardo Habkost <ehabkost@redhat.com>
> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> Message-Id: 
> <4cf1beb7dafb9143c261d266557d3173bf160524.1598376594.git.alistair.francis@wdc.com>
> ---
> @@ -269,13 +258,18 @@ static RegisterInfoArray 
> *register_init_block(DeviceState *owner,
>          int index = rae[i].addr / data_size;
>          RegisterInfo *r = &ri[index];
>
> -        *r = (RegisterInfo) {
> -            .data = data + data_size * index,
> -            .data_size = data_size,
> -            .access = &rae[i],
> -            .opaque = owner,
> -        };
> -        register_init(r);
> +        if (data + data_size * index == 0 || !&rae[i]) {
> +            continue;

Coverity thinks (CID 1432800) that this is dead code, because
"data + data_size * index" can never be NULL[*]. What was this
intending to test for ? (maybe data == NULL? Missing dereference
operator ?)

[*] The C spec is quite strict about what valid pointer arithmetic
is; in particular adding to a NULL pointer is undefined behaviour,
and pointer arithmetic that overflows and wraps around is
undefined behaviour, so there's no way to get a 0 result from
"ptr + offset" without the expression being UB.

thanks
-- PMM