[newlib-cygwin] Cygwin: signalfd: implement non-polling select

[Corinna Vinschen]

On Jan 15 10:50, Václav Haisman wrote:
> On Mon, 14 Jan 2019 at 17:19, Corinna Vinschen <corinna@sourceware.org> wrote:
> >
> > https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=f42776fa781de858a927bc03aa966a0f3096b581
> >
> > commit f42776fa781de858a927bc03aa966a0f3096b581
> > Author: Corinna Vinschen <corinna@vinschen.de>
> > Date:   Mon Jan 14 17:19:37 2019 +0100
> >
> >     Cygwin: signalfd: implement non-polling select
> >
> >     Allow the signal thread to recognize we're called in consequence of
> >     select on a signalfd.  If the signal is part of the wait mask, don't
> >     call any signal handler and don't remove the signal from the queue,
> >     so a subsequent read (or sigwaitinfo/sigtimedwait) still gets the
> >     signal.  Instead, just signal the event object at
> >     _cygtls::signalfd_select_wait for the thread running select.
> >
> >     The addition of signalfd_select_wait to _cygtls unearthed the alignment
> >     problem of the context member again.  To make sure this doesn't get lost,
> >     improve the related comment in the header file so that this (hopefully)
> >     doesn't get lost (again).
> >
> >     Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
> > [...]
> >
> > diff --git a/winsup/cygwin/cygtls.h b/winsup/cygwin/cygtls.h
> > index 39dba13..65a905c 100644
> > --- a/winsup/cygwin/cygtls.h
> > +++ b/winsup/cygwin/cygtls.h
> > @@ -189,8 +189,11 @@ public:
> >    stack_t altstack;
> >    siginfo_t *sigwait_info;
> >    HANDLE signal_arrived;
> > +  HANDLE signalfd_select_wait;
> >    bool will_wait_for_signal;
> > -  long __align;                        /* Needed to align context to 16 byte. */
> > +  /* context MUST be aligned to 16 byte, otherwise RtlCaptureContext fails.
> > +     If you prepend cygtls members here, make sure context stays 16 byte
> > +     aligned. */
> >    ucontext_t context;
> >[...]
> Would it not better to do this with `ucontext_t context
> __attribute__((__aligned__(16)));` instead?

In theory yes, but it doesn't work.  The simple perl parser in
gentls_offsets doesn't understand __attribute__ and screws up,
so generating tlsoffsets{64}.h fails.

I'm not good at perl.  My attempts to fix the parser to let
__attribute__ statements slip through unchanged failed so far.
Right now what it does is:

  ucontext_t context __attribute__((__aligned__(16)));

in the input is mangled to

  ucontext_t context__attribute____aligned__16;

in the output.  Any help appreciated.


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
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