On Thu, Aug 22, 2024 at 5:21 AM Adhemerval Zanella Netto
<adhemerval.zanella@xxxxxxxxxx> wrote:
>
>
>
> On 21/08/24 16:41, Alejandro Colomar wrote:
> > Hi Adhemerval, Elliott,
> >
> > On Wed, Aug 21, 2024 at 03:19:02PM GMT, Adhemerval Zanella Netto wrote:
> >> I would use either the kernel interface:
> >>
> >> arch/x86/kernel/process_64.c
> >> 961 SYSCALL_DEFINE2(arch_prctl, int, option, unsigned long, arg2)
> >>
> >> Where is seems to what most caller do, or maybe something like:
> >>
> >> union __arch_prctl_arg
> >> {
> >> unsigned long addr;
> >> unsigned long *vaddr;
> >> };
> >>
> >> int arch_prctl (int option, union __arch_prctl_arg *arg);
> >
> > Or you could use a transparent union:
> >
> > $ cat arch_prctl.c
> > union __attribute__((__transparent_union__)) __arch_prctl_arg {
> > unsigned long set;
> > unsigned long *get;
> > };
> >
> > int my_arch_prctl(int op, union __arch_prctl_arg arg2);
> >
> > int
> > main(void)
> > {
> > unsigned long u = 0;
> >
> > my_arch_prctl(1, u);
> > my_arch_prctl(1, &u);
> > }
> > $ gcc -Wall -Wextra -S arch_prctl.c
> > $
>
> Although we do use __transparent_union__ we have to still handle very old
> compilers:
We can hide the prototype for the older compilers. Softwares need to
deal with the missing prototype anyway.
> socket/sys/socket.h
>
> 51 /* This is the type we use for generic socket address arguments.
> 52
> 53 With GCC 2.7 and later, the funky union causes redeclarations or
> 54 uses with any of the listed types to be allowed without complaint.
> 55 G++ 2.7 does not support transparent unions so there we want the
> 56 old-style declaration, too. */
> 57 #if defined __cplusplus || !__GNUC_PREREQ (2, 7) || !defined __USE_GNU
>
> I guess this is not really required anymore.
>
> >
> >> And for constants, it would require a x86_64 specific sys/prctl.h header
> >> with either the has_include tricks to include the kernel one or to just
> >> copy the kernel one (along with possible a test to check the sync with
> >> kernel definitions).
> >
> > I think including would be simpler, if it's possible.
> >
> > I've seen some problems arise from copying kernel stuff in glibc
> > headers, such as being unable to include both a some kernel and some
> > glibc headers in the same program due to redefinitions.
> >
> >
> > Have a lovely night!
> > Alex
> >
> >
--
H.J.
