Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS)

[David Daney]

On 06/21/2013 01:22 PM, Oleg Nesterov wrote:
> On 06/21, David Daney wrote:
> > On 06/21/2013 06:39 AM, James Hogan wrote:
> > > Therefore add sig_to_exitcode() and exitcode_to_sig() functions which
> > > map signal numbers > 126 to exit code 126 and puts the remainder (i.e.
> > > sig - 126) in higher bits. This allows WIFSIGNALED() to return true for
> > > both SIG127 and SIG128, and allows WTERMSIG to be later updated to read
> > > the correct signal number for SIG127 and SIG128.
> >
> > I really hate this approach.
> >
> > Can we just change the ABI to reduce the number of signals so that all
> > the standard C library wait related macros don't have to be changed?
> >
> > Think about it, any user space program using signal numbers 127 and 128
> > doesn't work correctly as things exist today, so removing those two will
> > be no great loss.
>
> Oh, I agree.
>
> Besides, this changes ABI anyway. And if we change it we can do this in
> a more clean way, afaics. MIPS should simply use 2 bytes in exit_code for
> signal number.

Wouldn't that break *all* existing programs that use signals?  Perhaps I 
misunderstand what you are suggesting.

I am proposing that we just reduce the number of usable signals such 
that existing libc status checking macros/functions don't change in any way.

 Yes, this means we need replace 0x80/0x7f in exit.c by
> ifdef'ed numbers. And yes, this means that WIFSIGNALED/etc should be
> updated too, but this is also true with this patch.
>
> Oleg.

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