[Bug target/51007] New: Quadmath I/O doesn't work on MinGW

[Bug target/51007] New: Quadmath I/O doesn't work on MinGW

[fxcoudert at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51007

             Bug #: 51007
           Summary: Quadmath I/O doesn't work on MinGW
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: fxcoudert@gcc.gnu.org
            Target: i586-pc-mingw32


The following test program works fine with current trunk on i686 and
x86_64-linux:


#include <quadmath.h>
#include <stdio.h>

int main (void)
{
  char buf[100];
  quadmath_snprintf (buf, sizeof buf, "%.60Qg", (__float128) 3.14);
  puts (buf);
}


It outputs "3.140000000000000124344978758017532527446746826171875". When
compiled and run on MinGW, it gives an incorrect output (on my test system,
"1.9163987915738935076000483121420225908698150840344985584492e-4932"). I
confirmed with both a native MinGW build (i586-pc-mingw32) and a cross-compiler
for i586-pc-mingw32, running on x86_64-apple-darwin11, and running the result
under either Wine or a real Windows.

The cross-compiler is configured as such:


../../gcc/trunk/configure --target=i586-pc-mingw32 --disable-werror
--enable-languages=c,fortran

[Bug target/51007] Quadmath I/O doesn't work on MinGW

[fxcoudert at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51007

Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011-11-07
     Ever Confirmed|0                           |1

[Bug target/51007] Quadmath I/O doesn't work on MinGW

[fxcoudert at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51007

--- Comment #1 from Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> 2011-11-07 11:03:32 UTC ---
I don't know if it's related, or two different bugs, but hexadecimal printing
has the correct mantissa with a wrong exponent. See below the same testcase
compile on my mac (native compiler) and cross-compiled to mingw:

$ cat v.c 
#include <quadmath.h>
#include <stdio.h>

int main (void)
{
  char buf[100];
  quadmath_snprintf (buf, sizeof buf, "%.60Qa", (__float128) 3.14);
  puts (buf);
}
$ gcc-4.6 v.c -lquadmath && ./a.out 
0x1.91eb851eb851f00000000000000000000000000000000000000000000000p+1
$ ./cross/bin/i586-pc-mingw32-gcc v.c -static -lquadmath
$ /opt/wine/bin/wine ./a.exe 
0x1.91eb851eb851f00000000000000000000000000000000000000000000000p-5318

[Bug target/51007] Quadmath I/O doesn't work on MinGW

[fxcoudert at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51007

--- Comment #2 from Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> 2011-11-07 11:29:39 UTC ---
The bug is not in the I/O routine, it can be reproduce by this simple
self-contained testcase (which doesn't need libquadmath).

#include <stdint.h>

typedef union
{
  __float128 value;

  struct
  {
#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
    unsigned negative:1;
    unsigned exponent:15;
    uint64_t mant_high:48;
    uint64_t mant_low:64;
#else
    uint64_t mant_low:64;
    uint64_t mant_high:48;
    unsigned exponent:15;
    unsigned negative:1;
#endif
  } ieee;
} ieee854_float128;

int main (void)
{
  ieee854_float128 d;
  d.value = (__float128) 3.14;
  __builtin_printf ("%u\n", (unsigned) d.ieee.exponent);
}

On darwin, this program consistently outputs 16384. When cross-compiled to
mingw, and run on Windows XP, it consistently outputs 6448. When the same
executable is run under Wine on darwin, it outputs inconsistent, wrong values
(the last few invocations here show: 4755, 12947, 21139).

[Bug target/51007] Quadmath I/O doesn't work on MinGW

[fxcoudert at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51007

--- Comment #3 from Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> 2011-11-07 11:39:12 UTC ---
Going further: I tried to compare the trees generated by the simple function
below:


#include <stdint.h>

typedef union
{
  __float128 value;

  struct
  {
#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
    unsigned negative:1;
    unsigned exponent:15;
    uint64_t mant_high:48;
    uint64_t mant_low:64;
#else
    uint64_t mant_low:64;
    uint64_t mant_high:48;
    unsigned exponent:15;
    unsigned negative:1;
#endif
  } ieee;
} ieee854_float128;

unsigned foo (__float128 x)
{
  ieee854_float128 d;
  d.value = x;
  return d.ieee.exponent;
}


AFAICT, both the original and the optimized tree for darwin and mingw are
identical. The assembly code generated for a common arch (-march=core2 -O0)
differs:

***** on mingw *****
_foo:
        pushl   %ebp
        movl    %esp, %ebp
        subl    $40, %esp
        movdqa  8(%ebp), %xmm0
        movdqa  %xmm0, -40(%ebp)
        movzwl  -24(%ebp), %eax
        andw    $32767, %ax
        movzwl  %ax, %eax
        leave
        ret

***** on darwin *****
_foo:
    pushq    %rbp
    movq    %rsp, %rbp
    movdqa    %xmm0, -32(%rbp)
    movdqa    -32(%rbp), %xmm0
    movdqa    %xmm0, -16(%rbp)
    movzwl    -2(%rbp), %eax
    andw    $32767, %ax
    movzwl    %ax, %eax
    popq    %rbp
    ret


Now, my assembly skills are pretty close to nil, so I can't figure out if the
differences are meaningful, and what they mean. I only hope that I got it close
enough that someone can, from here, understand where this code generation come
from and how to fix it.

[Bug target/51007] Quadmath I/O doesn't work on MinGW

[ktietz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51007

--- Comment #4 from Kai Tietz <ktietz at gcc dot gnu.org> 2011-11-07 12:00:49 UTC ---
The issue is caused by bitfield layout.  For mingw targets the -mms-bitfields
option is for 4.7 active by default.

So  the mixture of different sized types in union is leading to this behavior.
You can see that result becomes ok, if you are specifying to union/struct the
attribute gcc_struct.

Cheers,
Kai

[Bug target/51007] Quadmath I/O doesn't work on MinGW

[ktietz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51007

--- Comment #5 from Kai Tietz <ktietz at gcc dot gnu.org> 2011-11-07 12:19:09 UTC ---
Suggested patch for this issue

ChangeLog

        * quadmath-imp.h (ieee854_float128): Adjust
        for ms-bitfield layout.

Index: quadmath-imp.h
===================================================================
--- quadmath-imp.h      (revision 180840)
+++ quadmath-imp.h      (working copy)
@@ -48,6 +48,11 @@
   __float128 value;

   struct
+#ifdef __MINGW32__
+  /* On mingw targets ms-bitfields option is active by default.
+     Therefore enforce gnu-bitfield style.  */
+  __attribute__ ((gcc_struct))
+#endif
   {
 #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
     unsigned negative:1;
@@ -89,6 +94,10 @@
   } words32;

   struct
+#ifdef __MINGW32__
+  /* Make sure we are using gnu-style bitfield handling.  */
+  __attribute__ ((gcc_struct))
+#endif
   {
 #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
     unsigned negative:1;

[Bug target/51007] Quadmath I/O doesn't work on MinGW

[fxcoudert at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51007

Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch
                 CC|                            |jakub at redhat dot com

--- Comment #6 from Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> 2011-11-07 12:42:26 UTC ---
(In reply to comment #4)
> So  the mixture of different sized types in union is leading to this behavior.
> You can see that result becomes ok, if you are specifying to union/struct the
> attribute gcc_struct.

Indeed, I confirm that your patch fixes the issue (and the original Fortran
testcase reported on comp.lang.fortran now works fine). Both Tobias and Jakub
(Cc'ed) are libquadmath maintainers and can approve it.

[Bug target/51007] Quadmath I/O doesn't work on MinGW

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51007

--- Comment #7 from Tobias Burnus <burnus at gcc dot gnu.org> 2011-11-07 15:29:52 UTC ---
(In reply to comment #5)
> ChangeLog
> 
>         * quadmath-imp.h (ieee854_float128): Adjust
>         for ms-bitfield layout.
> 
> +#ifdef __MINGW32__
> +  /* On mingw targets ms-bitfields option is active by default.
> +     Therefore enforce gnu-bitfield style.  */
> +  __attribute__ ((gcc_struct))
> +#endif

The patch looks fine to me - except that I would put an "the" before
"ms-bitfields option".

[Bug target/51007] [4.7 Regression] Quadmath I/O doesn't work on MinGW

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51007

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.7.0
            Summary|Quadmath I/O doesn't work   |[4.7 Regression] Quadmath
                   |on MinGW                    |I/O doesn't work on MinGW

[Bug target/51007] [4.7 Regression] Quadmath I/O doesn't work on MinGW

[ktietz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51007

--- Comment #8 from Kai Tietz <ktietz at gcc dot gnu.org> 2011-11-07 22:04:00 UTC ---
Author: ktietz
Date: Mon Nov  7 22:03:51 2011
New Revision: 181125

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=181125
Log:
        PR target/51007
        * quadmath-imp.h (ieee854_float128): Adjust
        for ms-bitfield layout.


Modified:
    trunk/libquadmath/ChangeLog
    trunk/libquadmath/quadmath-imp.h

[Bug target/51007] [4.7 Regression] Quadmath I/O doesn't work on MinGW

[ktietz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51007

Kai Tietz <ktietz at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #9 from Kai Tietz <ktietz at gcc dot gnu.org> 2011-11-07 22:05:31 UTC ---
Applied with suggested "the" before ms-bitfield option.
Fixed.

[Bug target/51007] [4.7 Regression] Quadmath I/O doesn't work on MinGW

[bkoz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51007

--- Comment #10 from Benjamin Kosnik <bkoz at gcc dot gnu.org> 2012-05-31 18:51:34 UTC ---
Author: bkoz
Date: Thu May 31 18:51:27 2012
New Revision: 188076

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=188076
Log:
2012-05-31  Benjamin Kosnik  <bkoz@redhat.com>

        PR libstdc++/51007
        * configure.ac: Allow gnu, gnu* variants for --enable-symvers argument.
        * configure: Regenerated.

Modified:
    trunk/libgfortran/ChangeLog
    trunk/libgfortran/configure
    trunk/libgfortran/configure.ac
    trunk/libquadmath/ChangeLog
    trunk/libquadmath/configure
    trunk/libquadmath/configure.ac
    trunk/libssp/ChangeLog
    trunk/libssp/configure
    trunk/libssp/configure.ac