Re: glibc 2.1.92 tst-getdate failure on linuxppc

[Geoff Keating <geoffk at cygnus dot com>]

> From: Franz Sirl <Franz.Sirl-kernel@lauterbach.com>
> Date: Sat, 26 Aug 2000 19:17:55 +0200

> Hmm, if I read the kernel source correctly, FPE0 and FPE1 are always
> set to 1 for user tasks, so do we really need to modify these bits?
> If not, we can just use _[SG]ET_FPUCW, or? Am I missing something

Please don't use _?ET_FPUCW for anything.  It's obsolete, and I've
heard it doesn't work :-).  Use the macros in fenv_libc.h instead.

> here?

Old kernels didn't do that, probably because it causes a factor-of-4
performance decrease on the 601.  I would hate to rely on it.

I think instead you can change these bits by causing a signal,
changing the bits in the signal's context in the signal handler, and
returning.  Try the attached.  I don't know of any way to test this
because handling of those bits is somewhat broken in current linux
kernels.

I guess if this works for you, just put it in place, and if the kernel
changes later it'll be their fault :-).

-- 
- Geoffrey Keating <geoffk@cygnus.com>

===File
~/cygnus/co/glibc-mainline/libc/sysdeps/unix/sysv/linux/powerpc/fe_nomask.c===
/* Procedure definition for FE_NOMASK_ENV for Linux/ppc.
   Copyright (C) 2000 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <fenv.h>
#include <errno.h>
#include <signal.h>
#include <unistd.h>

/* This is rather fiddly under Linux.  We don't have direct access,
   and there is no system call, but we can change the bits 
   in a signal handler's context...  */

static struct sigaction oact;

static void
fe_nomask_handler (int signum, struct sigcontext *sc)
{
  sc->regs->msr |= 0x900ul;  /* FE0 | FE1 */
  sigaction (SIGUSR1, &oact, NULL);
}

const fenv_t *
__fe_nomask_env(void)
{
  struct sigaction act;

  act.sa_handler = (sighandler_t) fe_nomask_handler;
  sigemptyset (&act.sa_mask);
  act.sa_flags = 0;

  sigaction (SIGUSR1, &act, &oact);
  raise (SIGUSR1);

  return FE_ENABLED_ENV;
}
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