On Tue, Jan 18, 2022 at 3:20 PM Alexander Monakov <amonakov@xxxxxxxxx> wrote:
>
> On Tue, 18 Jan 2022, Bin.Cheng via Gcc-help wrote:
>
> > Hi,
> > With -Waddress-of-packed-member option, GCC gives warning message if
> > address of packed structure member is taken and assigned to pointer,
> > like:
> > struct foo {
> > char a;
> > int b;
> > } __attribute__((packed));
> >
> > int main()
> > {
> > struct foo foo;
> > int *p;
> > p = &foo.b; // !!
> > *p = 1234;
> > return 0;
> > }
> >
> > This is expected, however, I wonder if there is any way to let gcc
> > know that `p` is a pointer that might be unaligned, so that an
> > unaligned access instruction is generated if `p` is dereferenced?
> > IIRC, microsoft compiler has __unaligned keyword extended for pointer
> > declaration.
>
> Sure, just add a new type with non-standard alignment. Instead of
> 'int *p' you can write e.g.
>
> typedef int i32u __attribute__((aligned(1)));
> i32u *p;
>
Hi Alexander,
Thanks very much for helping. This works.
However, I wonder what the difference is between typedef and the following code?
int __attribute__((aligned(1))) *p;
// ...
Thanks,
bin
