[PATCH 11/12] aarch64: redefine RETURN_ADDRESS to strip PAC

[Szabolcs Nagy]

The 05/08/2020 14:44, Adhemerval Zanella via Libc-alpha wrote:
> On 30/04/2020 14:45, Szabolcs Nagy wrote:
> > +++ b/sysdeps/aarch64/sysdep.h
> > @@ -35,6 +35,16 @@
> >  
> >  #define PTR_SIZE	(1<<PTR_LOG_SIZE)
> >  
> > +/* Strip pointer authentication code from pointer p.  */
> > +#define XPAC(p) ({					\
> > +  register void *__ra asm ("x30") = (p);		\
> > +  asm ("hint 7 // xpaclri" : "+r"(__ra));		\
> > +  __ra;})
> > +
> > +/* This is needed when glibc is built with -mbranch-protection=pac-ret.  */
> > +#undef RETURN_ADDRESS
> > +#define RETURN_ADDRESS(n) XPAC(__builtin_return_address(n))
> > +
> 
> Maybe use a inline function instead?

macro seems more reliable to me than always_inline
when poking at __builtin_return_address and x30,
but i'm not against always_inline if that's
considered better.

i'd prefer separate xpac (since it can be used
not just with __builtin_return_address e.g. for
stored code address in jmpbuf, which currently
uses ptrmangling)

>   #ifndef __ASSEMBLER__
>   # include <sys/cdefs.h>

what is cdefs.h for?

>   /* Strip pointer authentication code from pointer p.  */
>   static __always_inline void *
>   return_address (unsigned int n)
>   { 
>     register void *ra asm ("x30") = __builtin_return_address (n);
>     asm ("hint 7 // xpaclri" : "+r" (ra));
>     return ra;
>   }
> 
>   /* This is needed when glibc is built with -mbranch-protection=pac-ret.  */
>   # undef RETURN_ADDRESS
>   # define RETURN_ADDRESS(n) return_address (n)
>   #endif