Re: [libvirt] [PATCH] Cygwin's GCC doesn't like this .sa_handler initialization for some reason

On 04/25/2010 05:32 AM, Matthias Bolte wrote: > --- >  examples/domain-events/events-c/event-test.c |    7 ++++--- >  1 files changed, 4 insertions(+), 3 deletions(-) > > diff --git a/examples/domain-events/events-c/event-test.c b/examples/domain-events/events-c/event-test.c > index 53a3195..74eabba 100644 > --- a/examples/domain-events/events-c/event-test.c > +++ b/examples/domain-events/events-c/event-test.c > @@ -380,10 +380,11 @@ int main(int argc, char **argv) >      int callback5ret = -1; >      int callback6ret = -1; >      int callback7ret = -1; > +    struct sigaction action_stop; > > -    struct sigaction action_stop = { > -        .sa_handler = stop > -    }; > +    memset(&action_stop, 0, sizeof action_stop); > + > +    action_stop.sa_handler = stop; ACK.  By the way, the "for some reason" boils down to how sa_handler is declared in <signal.h> on the two platforms.  On cygwin, sa_handler happens to be a member of an anonymous union (exploiting a gcc extension); whereas on Linux, it is a macro that accesses a member of a named union.  If I read POSIX correctly, both behaviors for the declaration of sa_handler are permitted.  But dotted assignment only works in the case of a named union.  Whether it is a gcc bug that you can't use dotted assignment to access a member of an anonymous union, or a cygwin bug for having a header that does not allow compilation like Linux (when cygwin's stated goal is to be Linux-compatible) is debatable. By the way, this use of memset() to initialize action_stop assumes that the null pointer is all 0 bits (which is probably okay for all platforms that libvirt will ever run on).  There is currently a discussion on gnulib on the fact that to be portable to C99, where a null pointer might not be all 0 bits, you would instead have to use the more drawn-out sequence:

static struct sigaction zero_sigaction = {0}; struct sigaction action_stop = zero_sigaction; action_stop.sa_handler = stop; But don't go changing this commit just for that theoretical platform.