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:
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
>
>
