Re: adding extra signals for LinuxThreads (Re: Linux 2.1.69..)

[H. Peter Anvin]

Followup to:  <Pine.GSO.3.95.971206124215.23361B-100000@kielo>
By author:    =?ISO-8859-1?Q?Erkki_Sepp=E4l=E4?= <[e-mail]>
In newsgroup: linux.dev.kernel
> 
>   Hmm, I didn't think of that. But if there really is no another way to
> implement this, then this must be done sooner or later. Right? 
>   I don't think that adding another integer would introduce a major
> performance hit, but on the other hand, I don't know what I'm talking
> about :).
>   Also I've heard that some level of posix introduces custom signals, how
> are they going to be handled? I don't know anything more about this
> matter..
> 
> > There may also be binary compatibility problems to solve too.
> 
>   I guess that for ia32 platform there is no other way to 'blend' the code
> than to create a new system call, which accepts a 64-bit bitmask. And
> change libc too. Or maybe glibc2 already uses 64-bit masks, I don't know.
> 

glibc uses a much larger mask than that.  Either way, for most, but
not all platforms, there seems to be space:

	i386	31; 16 is SIGSTKFLT which is never generated
	alpha	_NSIG is 32, but it uses 64-bit masks already so it
		can be increased to 64 trivally
	m68k	31, 16 (SIGSTKFLT)
	mips	32-64 (yes, MIPS sets _NSIG to 65, not 64)
	ppc	31, 16 (SIGSTKFLT)
	sparc	Trouble.  Maybe we could overload SIGLOST or SIGSYS,
		but I don't know.  There seems to be a concept of
		major and minor signal numbers on the sparc; SIGILL,
		SIGEMT, SIGFPE and SIGBUS have minor numbers defined;
		maybe piggybacking is possible?
	sparc64 Same as sparc, but uses 64-bit masks for 64-bit
		processes.

I personally don't see any problem with overloading/recycling
SIGSTKFLT if it is indeed a signal that's never used.  sparc is
definitely trouble, though, but even a nonstandard signal overloading
would be better than using two signals specifically designated for the
end programmer.

	-hpa
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