Re: [ANNOUNCEMENT] Updated for 32-bit, new for 64-bit: libsigsegv-2.10-2

[Ken Brown <kbrown@cornell.edu>]

On 7/18/2015 2:18 PM, Eric Blake wrote:
> On 07/17/2015 05:22 PM, Eric Blake (cygwin) wrote:
>> A new release of libsigsegv, 2.10-2, will soon be available for download
>> from your favorite mirror.  On 32-bit cygwin, this leaves 2.10-1 as
>> previous; on 64-bit cygwin, it is a new port of the package, made
>> possible for the first time by new sigaltstack() code in cygwin 2.1.0.
>
> Oddly enough, this new library actually causes a regression in 32-bit m4
> - with libsigsegv-2.10-1, I get stack overflow handling, but with -2,
> attempting to register the handler fails and m4 ends up dumping core on
> stack overflow.  But it's not quite libsigsegv's fault.  m4 was
> originally creating an alternate stack of 16k in size, based on a pure
> guess that it would be large enough (since the headers didn't declare
> any constant otherwise); but cygwin's sigaltstack() requires an
> alternate stack of 64k or larger.
>
> I see a couple of options:
>
> 1. see if we can relax cygwin.dll to live with a 16k alternate stack
>
> 2. recompile every application that linked against libsigsegv to make
> use of cygwin's new constants (at least those applications like m4 that
> were using shared gnulib code to guess at the right stack size will now
> guess correctly, hand a larger stack to libsigsegv, and libsigsegv can
> then just use sigaltstack() as desired)
>
> 3. recompile libsigsegv for 32-bit to put in a hack: if the stack size
> passed by the caller is < 64k but >= 16k, then fall back to the older
> back-door Windows native stack overflow handling.
>
> Option 1 is risky and might not be possible; option 2 will happen
> eventually, but option 3 seems like the smoothest way to avoid breaking
> things while waiting to reach the point of option 2.  Of course, if we
> can get all maintainers to rebuild, then option 3 is wasted effort.
>
> How many applications would need to be rebuilt?  I see:
>
> diffutils [me]
> m4 [me]
> clisp [Ken Brown]

I was planning to rebuild 64-bit clisp anyway, to take advantage of the 
new libsigsegv, so I can rebuild on 32-bit also.  But there's no big 
rush, so I'll probably wait for Cygwin 2.2.0 unless someone reports a 
problem before then.

Ken