Hi Jon, On Mar 26 15:25, Jon TURNEY wrote: > Add ucontext.h header, defining ucontext_t and mcontext_t types. > > Provide sigaction sighandlers with a ucontext_t parameter containing a > mcontext_t with exception context information, if available. > > * include/sys/ucontext.h (__ucontext): New header. > * include/ucontext.h (_UCONTEXT_H): Ditto. > * exception.h (cygwin_exception): Add exception_record accessor. > * exceptions.cc (call_signal_handler): Provide ucontext_t > parameter to signal handler function, if available.
Thanks for this patch. Looks like a good idea.
But there are a few problems we should discuss first.
> +typedef struct __mcontext {
> + EXCEPTION_POINTERS *ep;
> +} mcontext_t;
> +
> +typedef struct __ucontext {
> + struct __ucontext *uc_link;
> + sigset_t uc_sigmask;
> + // We don't have a type stack_t, so we don't have a uc_stack member
> + mcontext_t uc_mcontext;
> +} ucontext_t;
* Per the Linux man page this structure should be called `struct
ucontext' without the underscores. However, we already have
definitions of `struct ucontext' in include/cygwin/signal.h... which
have nothing at all to do with the definition of ucontext on Linux.
This needs fixing.
Historically, the ucontext definition in cygwin/signal.h is equivalent
to the Windows thread CONTEXT definition. Why ever CONTEXT was used to
define ucontext beats me in retrospect.
It is used only when sending the thread context to a debugger when a
signal occured. The definition of struct ucontext from cygwin/signal.h
is only used as part of struct _cygtls (struct ucontext thread_context)
and then thread_context is used in _cygtls::signal_debugger, that's it.
Cygwin doesn't use it anywhere else.
GDB uses only the definition of __COPY_CONTEXT_SIZE from cygwin/signal.h,
but not the definition of struct ucontext. I sent a patch upstream to
get rid of that dependency.
We should remove or rename struct ucontext in cygwin/signal.h, so we
can use that name for your above struct __ucontext. That leads to the
next point...
* Since struct ucontext from cygwin/signal.h is actually a redefinition
of CONTEXT + an oldmask value. it's basically the Cygwin/Windows
representation of gregset_t + fpregset_t + cr2 + oldmask, aka
mcontext_t.
As for oldmask, this can be fetched easily from _my_tls, so in theory
we can use the current definition of ucontext from cygwin/signal.h as
mcontext_t.
But this drops the EXCEPTION_RECORD. I'm not sure it belongs here.
Keep in mind that a signal handler is not only called in case an
exception occured. I think the context is all a signal handler needs.
* As for stack_t, we have that. It's defined in newlib's sys/signal.h.
The stack base and stack size can be fetched from the TEB; with a
test for a user-defined stack, see pthread_wrapper in miscfuncs.cc.
While we're at it we should contemplate to define SIGSTKSZ and
MINSIGSTKSZ along the lines of 64K, I guess.
Thanks,
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat
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