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SubjectRe: [PATCH v2] signal: add procfd_signal() syscall
Andy Lutomirski <luto@amacapital.net> writes:

>> On Dec 1, 2018, at 7:28 AM, Eric W. Biederman <ebiederm@xmission.com> wrote:
>>
>>
>> It just occurs to me that the simple way to implement
>> procfd_sigqueueinfo info is like:
>>
>> int copy_siginfo_from_user_any(kernel_siginfo_t *info, siginfo_t *uinfo)
>> {
>> #ifdef CONFIG_COMPAT
>> if (in_compat_syscall)
>> return copy_siginfo_from_user32(info, uinfo);
>> #endif
>> return copy_siginfo_from_user(info, uinfo);
>> }
>>
>> long procfd_sigqueueinfo(int fd, siginfo_t *uinfo)
>> {
>> kernel_siginfo info;
>>
>> if (copy_siginfo_from_user_any(&info, uinfo))
>> return -EFAULT;
>> ...;
>> }
>>
>> It looks like there is already a place in ptrace.c that already
>> hand rolls copy_siginfo_from_user_any.
>>
>> So while I would love to figure out the subset of siginfo_t tha we can
>> just pass through, as I think that would make a better more forward
>> compatible copy_siginfo_from_user32.
>
> Seems reasonable to me. It’s less code overall than any other suggestion, too.
>
>> I think for this use case we just
>> add the in_compat_syscall test and then we just need to ensure this new
>> system call is placed in the proper places in the syscall table.
>>
>> Because we will need 3 call sights: x86_64, x32 and ia32. As the layout
>> changes between those three subarchitecuters.
>>
>>
>
> If it’s done this way, it can just be “common” in the 64-bit
> table. And we kick the can a bit farther down the road :)
>
> I’m working on patches to clean up x86’s syscall mess. It’s slow
> because I keep finding new messes. So far I have rt_sigreturn working
> like every other syscall — whee.
>
> Also, Eric, for your edification, I have a draft patch set to
> radically simplify x86’s signal delivery and return. Once that’s
> done, I can trivially speed up delivery by a ton by using sysret.

Nice.

Do we care about the performance of synchronous signal delivery (AKA
hardware exceptions) vs ordinary signal delivery. I get the feeling
there are serious simplifications to be had in that case.

Eric


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