Date: Wed, 29 Aug 2001 14:31:25 -0400 (EDT) From: Daniel Eischen <eischen@vigrid.com> To: Fuyuhiko Maruyama <fuyuhik8@is.titech.ac.jp> Cc: Arun Sharma <arun@sharmas.dhs.org>, hackers@FreeBSD.ORG Subject: Re: libc_r, signals and modifying sigcontext Message-ID: <Pine.SUN.3.91.1010829141318.10649A-100000@pcnet1.pcnet.com> In-Reply-To: <55k7zmiwop.wl@tripper.private>
next in thread | previous in thread | raw e-mail | index | archive | help
On Thu, 30 Aug 2001, Fuyuhiko Maruyama wrote:
> Hi all,
>
> I'm also wondering how to use signals to handle runtime exceptions
> such as SIGFPE and SIGSEGV in pthread application. These signals are
> often used by implementation of Java VM to handle Java's runtime
> exceptions. Almost same scheme works fine in non-pthread application
> but it doesn't in pthread application.
>
> `test.c' gives the simplified version of this problem (the program
> assumes x86). When I use _thread_sys_sigreturn someone suggests, the
> first signal is caught by signal handler on the current thread that
> cause the exception but signals after second attempts are never caught
> on the current thread. This is because the sigmask for signal handler
> thread, the current thread at first signal, is masked at
> uthread_sig.c(line 1070) and it isn't recovered when
> _thread_sys_sigreturn is called.
>
> So we need `sigreturn' function for libc_r instead of using
> _thread_sys_sigreturn. `uthread_sigreturn.c` gives a simple
> implementation of sigreturn for 4.3-STABLE(4.4-RC). When I use
> sigreturn (implemented at `uthread_sigreturn.c') instead
> of_thread_sys_sigreturn in `test.c', the program works as I expected.
>
>
> How do you think to add sigreturn function into libc_r?
Your implementation of sigreturn is not correct for our threads
library. You don't need the strong reference in -current.
The signal mask in the ucontext_t is the _process_ signal
mask. This is not the threads signal mask which can be
different. It may work in your case because your threads
don't change their signal mask, so it may be the same as
the process signal mask.
I'm not sure what sigreturn should do in a threaded environment,
particularly if it should restore the threads signal mask or
not. In order to make it work the you want it to, and I'm
not sure that is the correct thing yet, you need to change
the signal mask in the ucontext before the signal handler
is invoked. This would be done somewhere in uthread_sig.c.
You would put the threads signal mask (before OR'ing in
the sa_mask from the installed handler) into the ucontext.
This would make the ucontext passed to a signal handler
contain that threads signal mask, not the process signal
mask. Then when implementing sigreturn, you restore the
threads signal mask from the ucontext, place the process
signal mask in the ucontext, and _thread_sys_sigreturn().
Here's a quick (uncompiled, untested) attempt at a fix.
Index: uthread/uthread_sig.c
===================================================================
RCS file: /opt/FreeBSD/cvs/src/lib/libc_r/uthread/uthread_sig.c,v
retrieving revision 1.25.2.8
diff -u -r1.25.2.8 uthread_sig.c
--- uthread/uthread_sig.c 2001/07/06 12:31:25 1.25.2.8
+++ uthread/uthread_sig.c 2001/08/29 18:29:39
@@ -1063,6 +1063,7 @@
sizeof(psf->uc));
memcpy(&psf->siginfo, &_thread_sigq[psf->signo - 1].siginfo,
sizeof(psf->siginfo));
+ psf->uc.uc_sigmask = thread->sigmask;
}
/* Setup the signal mask: */
#include <sys/param.h>
#include <sys/types.h>
#include <sys/signalvar.h>
#include <signal.h>
#ifdef _THREAD_SAFE
#include <pthread.h>
#include "pthread_private.h"
int
_sigreturn(ucontext_t *ucp)
{
_thread_run->sigmask = ucp->uc_sigmask;
ucp->uc_sigmask = _process_sigmask;
return (_thread_sys_sigreturn(ucp));
}
__strong_reference(_sigreturn, sigreturn);
#endif
--
Dan Eischen
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.SUN.3.91.1010829141318.10649A-100000>