TEST RELEASE: Cygwin 2.1.0-0.2

Corinna Vinschen corinna-cygwin@cygwin.com
Mon Jun 22 14:30:00 GMT 2015

Hi Cygwin friends and users,

I released a second TEST version of Cygwin.  The version number is

This test release is mostly for interested *developers*.

The important news which needs some testing is the implementation of
sigaltstack(2) and the underlying implementation of running a signal
handler on the alternate signal stack.

Two changes to the previous test release, a fix to the sys/signal.h
header file which potentially broke building, and a change in the
assembler code preparing the alternate stack for the signal handler.

Implementation details:

- The alternate signal stack installed via sigaltstack is only valid for
  the current thread.  Each thread must call its own sigaltstack.  On
  pthread_create, the alternate signal stack setting of the calling
  thread is *not* propagated to the newly created thread.  This follows
  current Linux semantics.

- The alternate signal stack is a minimal stack.  Certain datastructures
  used by Cygwin (_cygtls area) and Windows (on 32 bit: exception
  records) are not copied over to the alternate signal stack.  The stack
  settings in the Thread Environment Block (TEB) are not reflecting the
  current alternate stack while running the signal handler.  The TEB
  will still point to the original thread stack.  This seems to work
  nicely in my testing, but there may be Windows functions which stop
  working in this scenario.

- The volatile registers and the original stack registers are stored at
  the base of the alternate stack.  If you screw this up while running
  the signal handler, your thread is doomed on return to the caller.

I'd be grateful if curious developers would give this new sigaltstack
implementation a whirl and report back if it's working for them as
desired/expected.  And if not, simple reproducers in plain C are most
welcome in this case.  Discussing aspects of this implementation may be
best handled on the cygwin-developers mailing list or the
#cygwin-developers IRC channel on Freenode.

All changes in this release so far:

What's new:

- First cut of an implementation to allow signal handlers running on an
  alternate signal stack.
- New API sigaltstack, plus definitions for SA_ONSTACK, SS_ONSTACK, SS_DISABLE,

- New API: sethostname.

Bug Fixes

- Enable non-SA_RESTART behaviour on threads other than main thread.
  Addresses: https://cygwin.com/ml/cygwin/2015-06/msg00260.html

- Try to handle concurrent close on socket more gracefully
  Addresses: https://cygwin.com/ml/cygwin/2015-06/msg00235.html

To install 32-bit Cygwin use https://cygwin.com/setup-x86.exe
To install 64 bit Cygwin use https://cygwin.com/setup-x86_64.exe

Have fun,

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

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