Re: [PATCH] PPC fenv fixes.

[Steven Munroe <munroesj at us dot ibm dot com>]

Steven Munroe wrote:
> Jakub Jelinek wrote:
>   
>> On Tue, Mar 27, 2007 at 11:09:28AM -0500, Steven Munroe wrote:
>>     
>>> 2007-03-26  Steven Munroe  <sjmunroe@us.ibm.com>
>>>
>>> 	* sysdeps/powerpc/fpu/feupdateenv.c: Change mask to merge exceptions
>>> 	from env.
>>>       
>> Will that actually raise SIGFPE signals when exceptions are enabled?
>> From my reading of POSIX that's what should happen with the
>> `old' exceptions (and other arches are calling feraiseexcept that will do
>> that).  I didn't add a testcase for it because I'm not 100% sure about that.
>>   
>>     
> hmmm not unless the SIGFPE is eanbled by the MSR FE bits. So we will
> need to call __fe_nomask_env() in feupdateenv similar to what we do in
> feenableexcept(). Probably should add the __fe_mask_env() call for when
> the application remasks FP exceptions. This allows the hardware to run
> faster when we are taking the default action.
>
> I will rework the patch.
>   
Merges my patch with one from Peter Bergner to use the prctl system to
eanble/disable FP exception when ever the FPSCR exeptions bits:
  FPSCR_VE,        /* invalid operation exception enable */
  FPSCR_OE,        /* overflow exception enable */
  FPSCR_UE,        /* underflow exception enable */
  FPSCR_ZE,        /* zero divide exception enable */
  FPSCR_XE,        /* inexact exception enable */

Change from all disabled to any enabled or any eanbled to all disabled.
This check was already in feenableexcept(). This patch adds the
appropriate eanble/disable calls to fedisableexcept() and __feupdateenv().


2007-03-26  Steven Munroe  <sjmunroe@us.ibm.com>
            Peter Bergner  <bergner@us.ibm.com>

	* sysdeps/powerpc/Versions (GLIBC_2.4): Add __fe_mask_env.
	* sysdeps/powerpc/bits/fenv.h: Declare __fe_nomask_env extern.
	Define FE_MASK_ENV.
	* sysdeps/powerpc/fpu/fe_mask.c: New file.
	* sysdeps/powerpc/fpu/fedisblxcpt.c (fedisableexcept):
	Call __fe_mask_env if all FP exceptions disabled.
	* sysdeps/powerpc/fpu/feupdateenv.c (__feupdateenv): Change mask to
	merge exceptions from env.  Use FE_NOMASK_ENV or FE_MASK_ENV when
	transitioning from all exceptions disabled to any exception enabled
	or visa versa.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/fe_mask.c: New file.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/fe_mask.c: New file.

diff -urN libc25-cvstip-20070320/sysdeps/powerpc/Versions libc25/sysdeps/powerpc/Versions
--- libc25-cvstip-20070320/sysdeps/powerpc/Versions	2004-02-13 21:25:10.000000000 -0600
+++ libc25/sysdeps/powerpc/Versions	2007-03-27 17:00:20.662310456 -0500
@@ -3,6 +3,10 @@
     # symbols used in macros from sysdeps/powerpc/bits/fenv.h
     __fe_dfl_env; __fe_enabled_env; __fe_nonieee_env; __fe_nomask_env;
   }
+  GLIBC_2.4 {
+    # symbols used in macros from sysdeps/powerpc/bits/fenv.h
+    __fe_mask_env;
+  }
 }
 
 libc {
diff -urN libc25-cvstip-20070320/sysdeps/powerpc/bits/fenv.h libc25/sysdeps/powerpc/bits/fenv.h
--- libc25-cvstip-20070320/sysdeps/powerpc/bits/fenv.h	2002-10-17 17:38:37.000000000 -0500
+++ libc25/sysdeps/powerpc/bits/fenv.h	2007-03-27 13:59:43.475316488 -0500
@@ -142,4 +142,8 @@
    performance penalty (but have no other visible effect).  */
 extern const fenv_t *__fe_nomask_env (void);
 # define FE_NOMASK_ENV	(__fe_nomask_env ())
+
+/* Floating-point environment with all exceptions disabled.  */
+extern const fenv_t *__fe_mask_env (void);
+# define FE_MASK_ENV	(__fe_mask_env ())
 #endif
diff -urN libc25-cvstip-20070320/sysdeps/powerpc/fpu/Makefile libc25/sysdeps/powerpc/fpu/Makefile
--- libc25-cvstip-20070320/sysdeps/powerpc/fpu/Makefile	2004-05-25 23:33:09.000000000 -0500
+++ libc25/sysdeps/powerpc/fpu/Makefile	2007-03-27 14:49:12.307388232 -0500
@@ -1,5 +1,5 @@
 ifeq ($(subdir),math)
-libm-support += fenv_const fe_nomask t_sqrt
+libm-support += fenv_const fe_nomask fe_mask t_sqrt
 
 # libm needs ld.so to access dl_hwcap
 $(objpfx)libm.so: $(elfobjdir)/ld.so
diff -urN libc25-cvstip-20070320/sysdeps/powerpc/fpu/fe_mask.c libc25/sysdeps/powerpc/fpu/fe_mask.c
--- libc25-cvstip-20070320/sysdeps/powerpc/fpu/fe_mask.c	Wed Dec 31 18:00:00 1969
+++ libc25/sysdeps/powerpc/fpu/fe_mask.c	Tue Mar 27 13:59:43 2007
@@ -0,0 +1,32 @@
+/* Procedure definition for FE_MASK_ENV.
+   Copyright (C) 2007 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 Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; 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>
+
+/* This is presently a stub, until it's decided how the kernels should
+   support this.  */
+
+const fenv_t *
+__fe_mask_env(void)
+{
+  __set_errno (ENOSYS);
+  return FE_DFL_ENV;
+}
+stub_warning (__fe_mask_env)
diff -urN libc25-cvstip-20070320/sysdeps/powerpc/fpu/fedisblxcpt.c libc25/sysdeps/powerpc/fpu/fedisblxcpt.c
--- libc25-cvstip-20070320/sysdeps/powerpc/fpu/fedisblxcpt.c	2001-07-05 23:56:02.000000000 -0500
+++ libc25/sysdeps/powerpc/fpu/fedisblxcpt.c	2007-03-27 13:59:43.494313600 -0500
@@ -24,7 +24,7 @@
 fedisableexcept (int excepts)
 {
   fenv_union_t fe;
-  int result;
+  int result, new;
 
   result = fegetexcept ();
 
@@ -44,7 +44,11 @@
     fe.l[1] &= ~(1 << (31 - FPSCR_VE));
   fesetenv_register (fe.fenv);
 
-  if ((fegetexcept () & excepts) != 0)
+  new = fegetexcept ();
+  if (new == 0 && result != 0)
+    (void)__fe_mask_env ();
+
+  if ((new & excepts) != 0)
     result = -1;
   return result;
 }
diff -urN libc25-cvstip-20070320/sysdeps/powerpc/fpu/feupdateenv.c libc25/sysdeps/powerpc/fpu/feupdateenv.c
--- libc25-cvstip-20070320/sysdeps/powerpc/fpu/feupdateenv.c	2001-07-05 23:56:02.000000000 -0500
+++ libc25/sysdeps/powerpc/fpu/feupdateenv.c	2007-03-27 16:50:49.810423368 -0500
@@ -1,5 +1,5 @@
 /* Install given floating-point environment and raise exceptions.
-   Copyright (C) 1997,99,2000,01 Free Software Foundation, Inc.
+   Copyright (C) 1997,99,2000,01,07 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
 
@@ -30,8 +30,24 @@
   new.fenv = *envp;
   old.fenv = fegetenv_register ();
 
-  /* Copy the set exceptions from `old' to `new'.  */
-  new.l[1] = (new.l[1] & 0xE00000FF) | (old.l[1] & 0x1FFFFF00);
+  /* Restore rounding mode and exception enable from *envp and merge
+     exceptions.  Leave fraction rounded/inexact and FP result/CC bits
+     unchanged.  */
+  new.l[1] = (old.l[1] & 0x1FFFFF00) | (new.l[1] & 0x1FF80FFF);
+  
+  /* If the old env has no eabled exceptions and the new env has any enabled
+     exceptions, then unmask SIGFPE in the MSR FE0/FE1 bits.  This will put
+     the hardware into "precise mode" and may cause the FPU to run slower on
+     some hardware.  */
+  if ((old.l[1] & 0x000000F8) == 0 && (new.l[1] & 0x000000F8) != 0)
+    FE_NOMASK_ENV;
+  
+  /* If the old env had any eabled exceptions and the new env has no enabled
+     exceptions, then mask SIGFPE in the MSR FE0/FE1 bits.  This may allow the
+     FPU to run faster because it always takes the default action and can not 
+     generate SIGFPE. */
+  if ((old.l[1] & 0x000000F8) != 0 && (new.l[1] & 0x000000F8) == 0)
+    FE_MASK_ENV;
 
   /* Atomically enable and raise (if appropriate) exceptions set in `new'. */
   fesetenv_register (new.fenv);
diff -urN libc25-cvstip-20070320/sysdeps/unix/sysv/linux/powerpc/powerpc32/fe_mask.c libc25/sysdeps/unix/sysv/linux/powerpc/powerpc32/fe_mask.c
--- libc25-cvstip-20070320/sysdeps/unix/sysv/linux/powerpc/powerpc32/fe_mask.c	Wed Dec 31 18:00:00 1969
+++ libc25/sysdeps/unix/sysv/linux/powerpc/powerpc32/fe_mask.c	Tue Mar 27 13:59:43 2007
@@ -0,0 +1,68 @@
+/* Procedure definition for FE_MASK_ENV for Linux/ppc.
+   Copyright (C) 2007 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 Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; 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>
+#include <sysdep.h>
+#include <sys/prctl.h>
+#include <kernel-features.h>
+
+#if __ASSUME_NEW_PRCTL_SYSCALL == 0
+/* 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_mask_handler (int signum, struct sigcontext *sc)
+{
+  sc->regs->msr &= ~0x900ul;  /* FE0 | FE1 */
+  sigaction (SIGUSR1, &oact, NULL);
+}
+#endif
+
+const fenv_t *
+__fe_mask_env (void)
+{
+#if __ASSUME_NEW_PRCTL_SYSCALL == 0
+# if defined PR_SET_FPEXC && defined PR_FP_EXC_DISABLED
+  int result = INLINE_SYSCALL (prctl, 2, PR_SET_FPEXC, PR_FP_EXC_DISABLED);
+
+  if (result == -1 && errno == EINVAL)
+# endif
+    {
+      struct sigaction act;
+
+      act.sa_handler = (sighandler_t) fe_mask_handler;
+      sigemptyset (&act.sa_mask);
+      act.sa_flags = 0;
+
+      sigaction (SIGUSR1, &act, &oact);
+      raise (SIGUSR1);
+    }
+#else
+  INTERNAL_SYSCALL_DECL (err);
+  INTERNAL_SYSCALL (prctl, err, 2, PR_SET_FPEXC, PR_FP_EXC_DISABLED);
+#endif
+
+  return FE_DFL_ENV;
+}
diff -urN libc25-cvstip-20070320/sysdeps/unix/sysv/linux/powerpc/powerpc64/fe_mask.c libc25/sysdeps/unix/sysv/linux/powerpc/powerpc64/fe_mask.c
--- libc25-cvstip-20070320/sysdeps/unix/sysv/linux/powerpc/powerpc64/fe_mask.c	Wed Dec 31 18:00:00 1969
+++ libc25/sysdeps/unix/sysv/linux/powerpc/powerpc64/fe_mask.c	Tue Mar 27 13:59:43 2007
@@ -0,0 +1,43 @@
+/* Procedure definition for FE_MASK_ENV for Linux/ppc64.
+   Copyright (C) 2007 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 Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; 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 <sysdep.h>
+#include <sys/syscall.h>
+#include <sys/prctl.h>
+#include <kernel-features.h>
+
+const fenv_t *
+__fe_mask_env (void)
+{
+#if defined PR_SET_FPEXC && defined PR_FP_EXC_DISABLED
+  int result;
+  INTERNAL_SYSCALL_DECL (err);
+  result = INTERNAL_SYSCALL (prctl, err, 2, PR_SET_FPEXC, PR_FP_EXC_DISABLED);
+# ifndef __ASSUME_NEW_PRCTL_SYSCALL
+  if (INTERNAL_SYSCALL_ERROR_P (result, err)
+      && INTERNAL_SYSCALL_ERRNO (result, err) == EINVAL)
+    __set_errno (ENOSYS);
+# endif
+#else
+  __set_errno (ENOSYS);
+#endif
+  return FE_DFL_ENV;
+}