Re: [PATCH v2] signal: add procfd_signal() syscall

[Christian Brauner]

On December 1, 2018 5:35:45 AM GMT+13:00, Andy Lutomirski <luto@xxxxxxxxxx> wrote:
>On Fri, Nov 30, 2018 at 3:41 AM Arnd Bergmann <arnd@xxxxxxxx> wrote:
>> siginfo_t as it is now still has a number of other downsides, and
>Andy in
>> particular didn't like the idea of having three new variants on x86
>> (depending on how you count). His alternative suggestion of having
>> a single syscall entry point that takes a 'signfo_t __user *' but
>interprets
>> it as compat_siginfo depending on
>in_compat_syscall()/in_x32_syscall()
>> should work correctly, but feels wrong to me, or at least
>inconsistent
>> with how we do this elsewhere.
>
>If everyone else is okay with it, I can get on board with three
>variants on x86.  What I can't get on board with is *five* variants on

Thanks Andy, that helps a lot.
I'm okay with it. Does this require any additional changes to how the syscall
is currently hooked up?

>x86, which would be:
>
>procfd_signal via int80 / the 32-bit vDSO: the ia32 structure
>
>syscall64 with nr == 335 (presumably): 64-bit
>
>syscall64 with nr == 548 | 0x40000000: x32
>
>syscall64 with nr == 548: 64-bit entry but in_compat_syscall() ==
>true, behavior is arbitrary
>
>syscall64 with nr == 335 | 0x40000000: x32 entry, but
>in_compat_syscall() == false, behavior is arbitrary
>
>This mess isn't really Christian's fault -- it's been there for a
>while, but it's awful and I don't think we want to perpetuate it.
>
>Obviously, I'd prefer a variant where the structure that's passed in
>is always the same.
>
>BTW, do we consider siginfo_t to be extensible?  If so, and if we pass

I would prefer if we could consider it extensible.
If so I would prefer if we could pass in a size argument.

>in a pointer, presumably we should pass a length as well.