[PATCH v6 1/2] aarch64: add support for hwcap3,4

[Yury Khrustalev]

On Tue, May 13, 2025 at 10:50:54AM -0400, enh wrote:
> On Tue, May 13, 2025 at 10:13 AM Yury Khrustalev
> <yury.khrustalev@arm.com> wrote:
> >
> > Add basic support for hwcap3 and hwcap4 in dynamic loader and
> > ifunc resolvers.
> > ...
> > -/* Second argument to an ifunc resolver.  */
> >  struct __ifunc_arg_t
> >  {
> > -  unsigned long _size; /* Size of the struct, so it can grow.  */
> > +  unsigned long _size;    /* Size of the struct, so it can grow.  */
> >    unsigned long _hwcap;
> > -  unsigned long _hwcap2;
> > +  unsigned long _hwcap2;  /* End of 1st published struct.  */
> > +  unsigned long _hwcap3;
> > +  unsigned long _hwcap4;  /* End of 2nd published struct.  */
> 
> (i'm ambivalent about adding the extra named fields here, because i
> think it discourages folks from switching to the helper function ---
> and if you've got a header new enough for the extra named fields, you
> also have the helper function. but if glibc adds these, i'll add them
> to bionic too, for source compatibility.)
> 

I think it's better to be consistent here. We already have two fields, and
if we don't add new once, then this struct will be forever incomplete, and
I think this will look somewhat confusing.

> >  };
> >
> > +#define _IFUNC_ARG_SIZE_VER0 24 /* sizeof 1st published struct */
> > +#define _IFUNC_ARG_SIZE_VER1 40 /* sizeof 2nd published struct */
> 
> (but i _won't_ add these to bionic --- i can't think of any _good_ use
> for these, only mischief.)

Glibc does this for internal static asserts that are handy for the future
programmers who make a change and may forget to update other related parts
(see for example struct clone_args). So, I thought it makes sense to have
these macros here too.


Kind regards,
Yury