Re: sigset_t for new arches

[Vineet Gupta <Vineet dot Gupta1 at synopsys dot com>]

On 11/13/2017 02:54 PM, H.J. Lu wrote:
> On Mon, Nov 13, 2017 at 2:29 PM, Vineet Gupta
> <Vineet.Gupta1@synopsys.com> wrote:
> > Hi,
> >
> > This came to light when initial testing ARC port to glibc.
> >
> > ARC glibc sigaction wrapper was failing as Linux kernel expects sa_mask
> > (sigset_t) to be 2 words (for the asm-generic syscall ABI mandated for newer
> > arches) while glibc defines it to be 32 words.
> >
> > The quick fix is to lie to kernel about it - and following works. This is
> > also approach taken by few other arches.
> >
> >          return INLINE_SYSCALL(rt_sigaction, 4,
> > -                       sig, act, oact, sizeof(act->sa_mask));
> > +                      sig, act, oact, _NSIG / 8);
> >
> >
> > However, IMHO, it would be nicer to just define sigset_t to be 2 words wide
> > for the relevant arch. If nothing else it would conserver some memory.
> >
> > My proposal is to define _SIGSET_NWORDS per arch in some header, with a
> > fallback header defaulting to what the current value is. Does this make
> > sense ? If yes, should this be in a new header or put in existing hdr etc.
>
> No.  See:
>
> https://sourceware.org/ml/libc-alpha/2017-11/msg00412.html

I don't see how this is solving the case of sigaction() where kernel is expecting 
2 * 4 bytes, but glibc has it defined as 32 * 4. Perhaps your work needs to be 
extended to more syscalls.