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

On Jul 19 10:37, Corinna Vinschen wrote:
> On Jul 18 14:41, Eric Blake wrote:
> > On 07/18/2015 02:11 PM, Corinna Vinschen wrote:
> > > OTOH, calling certain Cygwin functions might require lots of stack.
> > > E.g. open/read/write/close requires more than 2K stack, so MINSIGSTKSZ
> > > shouldn't be too small.
> > > 
> > > So, what about MINSIGSTKSZ == 8192 and SIGSTKSZ == 32768?
> > > 
> > > Or MINSIGSTKSZ == 16384 and SIGSTKSZ == 65536?
> > > 
> > > That could go into Cygwin 2.2.0 which I could release next week.
> > 
> > Might help, but feels a little unclean.  As I said, old clients of
> > libsigsegv were using the fallback definition of 16k; setting
> > MINSIGSTKSZ to 16k would let the sigaltstack() succeed where it is now
> > failing, but if cygwin ever consumes all 16k rather than the current 400
> > or so bytes, that leaves nothing for the application (normally, an
> > application only expects to use SIGSTKSZ - MINSIGSTKSZ for its own use,
> > if it uses the system-recommended sizing).
> Cygwin shouldn't really consume 16K stack by itself when called from the
> application.  Large buffers should use the tmp_pathbuf facility throughout.
> But there are still functions using big stack buffers.  I mention them
> here for bookkeeping as much as for information and discussion:
> - Debugging code in, initial_env() uses 96K stack on process
>   startup.  Usually disabled.  Non-critical.
> - dll_list::alloc, called during DLL initialization uses 64K stack.
>   Calling dlopen from the alternate stack would be fatal.  The buffer
>   is used in code called under Windows loader lock conditions, so this
>   could be converted to a static buffer.
> - A function called error_start_init uses 32K of stack and is called
>   if the env var CYGWIN is set to "error_init:...".  That's very unlikely
>   from a SEGV handler.  Not nice, but probably non-critical.
> - pinfo::status_exit is called when a process exits due to a signal
>   from Windows.  This usually shouldn't happen inside the signal
>   handler, but it might.  pinfo::status_exit uses a 32K buffer.
> - Stracing a process ends up using >48K of stack.
> That means even the current 32K are not quite sufficient, though, only
> in unlikely border cases, apparently.
> Anyway, I plan to change this in the next few days.  Given this, I'll
> set MINSIGSTKSZ to 8K and SIGSTKSZ to 32K in 2.2.

I uploaded snapshots as well as a 2.2.0-0.1 test release.  Please
give it a try.


Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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