[Bug math/15491] New: x86 nearbyint implementations wrongly clear all exceptions

[Bug math/15491] New: x86 nearbyint implementations wrongly clear all exceptions

[jsm28 at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=15491

             Bug #: 15491
           Summary: x86 nearbyint implementations wrongly clear all
                    exceptions
           Product: glibc
           Version: 2.17
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
        AssignedTo: unassigned@sourceware.org
        ReportedBy: jsm28@gcc.gnu.org
    Classification: Unclassified


The implementations of nearbyint functions using x87 floating point (x86 all
versions, x86_64 long double only) use the fclex instruction, which clears any
exceptions that were raised before the function was called.  These functions
must not clear exceptions that were raised before they were called.

I think fixing this will require saving and restoring the whole floating-point
environment as the way of avoiding raising "inexact" (which is what fesetenv
does, so use of frndint should still be faster than the C versions) - except
that if frndint raises an "invalid" exception for a sNaN operand, that *should*
be added into the restored environment.

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[Bug math/15491] [i386/x86_64] x86 nearbyint implementations wrongly clear all exceptions

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=15491

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
               Host|                            |i?86-*-* x86_64-*-*
            Summary|x86 nearbyint               |[i386/x86_64] x86 nearbyint
                   |implementations wrongly     |implementations wrongly
                   |clear all exceptions        |clear all exceptions

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[Bug math/15491] [i386/x86_64] x86 nearbyint implementations wrongly clear all exceptions

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15491

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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[Bug math/15491] [i386/x86_64] x86 nearbyint implementations wrongly clear all exceptions

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=15491

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
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The branch, master has been updated
       via  846d9a4a3acdb4939ca7bf6aed48f9f6f26911be (commit)
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=846d9a4a3acdb4939ca7bf6aed48f9f6f26911be

commit 846d9a4a3acdb4939ca7bf6aed48f9f6f26911be
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Thu Oct 22 23:14:55 2015 +0000

    Fix i386 / x86_64 nearbyint exception clearing (bug 15491).

    The implementations of nearbyint functions using x87 floating point
    (i386 all versions, x86_64 long double only) use the fclex
    instruction, which clears any exceptions that were raised before the
    function was called.  These functions must not clear exceptions that
    were raised before they were called.

    This patch fixes these functions to save and restore the whole
    floating-point environment (fnstenv / fldenv) as the way of avoiding
    raising "inexact" (recall that there isn't an x87 instruction for
    loading just the status word, so the whole environment has to be saved
    and loaded instead - the code already saved and loaded the control
    word, which is now obtained from the saved environment after this
    patch, to disable traps on "inexact").  In the case of the long double
    functions, any "invalid" exception from frndint (applied to a
    signaling NaN) needs merging into the saved state; this issue doesn't
    apply to the float and double functions because that exception would
    have been raised when the argument is loaded, before the environment
    is saved.

        [BZ #15491]
        * sysdeps/i386/fpu/s_nearbyint.S (__nearbyint): Save and restore
        floating-point environment instead of clearing all exceptions.
        * sysdeps/i386/fpu/s_nearbyintf.S (__nearbyintf): Likewise.
        * sysdeps/i386/fpu/s_nearbyintl.S (__nearbyintl): Likewise,
        merging in "invalid" exceptions from frndint.
        * sysdeps/x86_64/fpu/s_nearbyintl.S (__nearbyintl): Likewise.
        * math/test-nearbyint-except.c: New file.
        * math/Makefile (tests): Add test-nearbyint-except.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                         |   12 +++++
 NEWS                              |   24 +++++-----
 math/Makefile                     |    2 +-
 math/test-nearbyint-except.c      |   82 +++++++++++++++++++++++++++++++++++++
 sysdeps/i386/fpu/s_nearbyint.S    |   23 ++++------
 sysdeps/i386/fpu/s_nearbyintf.S   |   23 ++++------
 sysdeps/i386/fpu/s_nearbyintl.S   |   26 +++++------
 sysdeps/x86_64/fpu/s_nearbyintl.S |   14 ++++---
 8 files changed, 145 insertions(+), 61 deletions(-)
 create mode 100644 math/test-nearbyint-except.c

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[Bug math/15491] [i386/x86_64] x86 nearbyint implementations wrongly clear all exceptions

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=15491

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |2.23

--- Comment #2 from Joseph Myers <jsm28 at gcc dot gnu.org> ---
Fixed for 2.23.

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