On Wed, Apr 22, 2020 at 1:14 PM Eric Botcazou <botca...@adacore.com> wrote:
>
> > I notice this statement in the documentation:
> > Moreover, the use of type punning or aliasing to toggle the storage
> > order is not supported; that is to say, a given scalar object cannot
> > be accessed through distinct types that assign a different storage
> > order to it.
> > --- CUT ---
> > But I am not 100% sure that is the case here but I hope I am wrong in
> > saying this is not supported.
>
> This seems to me a fairly standard example of type punning:
>
> uint32_t u = 0x12345678;
> uint32_t bu = ((upal_u32be_t*)&u)->val;
>
> u = 0x12345678;
> uint32_t lu = ((upal_u32le_t*)&u)->val;
>
> u is accessed through upal_u32be_t and upal_u32le_t, i.e. BE and LE.
What if we had this:
uint32_t u = 0x12345678;
upal_u32be_t tempb;
memcpy (&tempb, &u, sizeof(uint32_t));
uint32_t bu = tempb.val;
Is that valid? We still run into the wrong code with the above case.
memcpy here should be considered a byte-by-byte copy and therefor
should not have any type punning except for to bytes.
Thanks,
Andrew Pinski
>
> --
> Eric Botcazou
