[Bug libfortran/31880] New: silent data corruption in gfortran read statement

[Bug libfortran/31880] New: silent data corruption in gfortran read statement

[roconnor at health dot usf dot edu]

This program should print out "1".
Instead, it prints out "1024":

      program r3

      integer*4 a(1025),b(1025),c(1025),d(2048),e(1022)

      do i=1,2048
         d(i)=i
      end do

      open  (3,file='a',form='unformatted')
      write (3) a,b,c,d,e
      rewind 3
      read  (3) a,b,c,d
      close (3)

      print *,d(1)

      end

output of /opt/bin/gfortran -v:

Using built-in specs.
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-4.1.2/configure --prefix=/opt --disable-multilib
Thread model: posix
gcc version 4.1.2

It was compiled with:
/opt/bin/gfortran -Wall -o r3 r3.f

and run with:
LD_LIBRARY_PATH=/opt/lib64 ./r3

This patch fixes it:

--- gcc-4.1-4.1.2/gcc-4.1.2/libgfortran/io/unix.c       2006-05-29
22:51:26.000000000 -0400
+++ gcc-4.1-4.1.2_patched/gcc-4.1.2/libgfortran/io/unix.c       2007-05-08
19:22:09.000000000 -0400
@@ -465,7 +465,7 @@
       if (n < 0)
        return NULL;

-      s->physical_offset = where + n;
+      s->physical_offset = m + n;
       s->active += n;
     }
   else
@@ -476,7 +476,7 @@
       if (do_read (s, s->buffer + s->active, &n) != 0)
        return NULL;

-      s->physical_offset = where + n;
+      s->physical_offset = m + n;
       s->active += n;
     }


The problem is that s->physical_offset is being miscalculated as
where+n, which is the requested read start address plus the bytes read
from the disk to fill the buffer.  It should be where+s->active+n
(=m+n), the requested read start address plus the as-yet-unread bytes
still in the buffer plus the bytes read from the disk to fill the
buffer.  The s->logical_offset is correctly set to where+*len.

What happens is that if an unbuffered (<8192 bytes) read of more than
half the buffer (array b in the example) exceeds the data remaining in
the buffer, the remaining data will get moved to the beginning of the
buffer, and some amount of data will be read from disk to fill the
buffer.  If the next read (array c) is of the same length, it will
also exceed the data remaining in the buffer, the remaining data will
get moved to the beginning of the buffer, and this time the length of
the data read from the disk (n) will be the same as the requested read
length (*len).  Since the physical_offset is being set to where+n and
s->logical_offset is set to where+*len, they are equal.  If the next
read is >=8192 bytes (array d), it will be unbuffered, which would
normally cause the data remaining in the buffer to be ignored and
cause a seek to re-read that data along with the rest of the request,
from the disk.  But the code will decide that it doesn't have to seek
because physical_offset=logical_offset.  So the remaining data in the
buffer will be lost.


-- 
           Summary: silent data corruption in gfortran read statement
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: libfortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: roconnor at health dot usf dot edu
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] silent data corruption in gfortran read statement

[fxcoudert at gcc dot gnu dot org]

------- Comment #1 from fxcoudert at gcc dot gnu dot org  2007-05-09 19:18 -------
Confirmed on i686-linux, for all active branches.


-- 

fxcoudert at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jvdelisle at gcc dot gnu dot
                   |                            |org, fxcoudert at gcc dot
                   |                            |gnu dot org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
  GCC build triplet|x86_64-unknown-linux-gnu    |
   GCC host triplet|x86_64-unknown-linux-gnu    |
 GCC target triplet|x86_64-unknown-linux-gnu    |
           Keywords|                            |patch, wrong-code
      Known to fail|                            |4.1.3 4.2.0 4.3.0
   Last reconfirmed|0000-00-00 00:00:00         |2007-05-09 19:18:26
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] silent data corruption in gfortran read statement

[kargl at gcc dot gnu dot org]

------- Comment #2 from kargl at gcc dot gnu dot org  2007-05-10 00:47 -------
(In reply to comment #1)
> Confirmed on i686-linux, for all active branches.
> 

I'm not sure how you can confirm this.  The program is invalid.
a,b,c, and e are undefined in the write statement, so gfortran 
can do whateve it wants.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] silent data corruption in gfortran read statement

[roconnor2 at tampabay dot rr dot com]

------- Comment #3 from roconnor2 at tampabay dot rr dot com  2007-05-10 01:02 -------
(In reply to comment #2)
> (In reply to comment #1)
> > Confirmed on i686-linux, for all active branches.
> > 
> 
> I'm not sure how you can confirm this.  The program is invalid.
> a,b,c, and e are undefined in the write statement, so gfortran 
> can do whateve it wants.
> 

This also exhibits the bug:

      program r3

      integer*4 a(1025),b(1025),c(1025),d(2048),e(1022)

      a = 0
      b = 0
      c = 0
      e = 0

      do i=1,2048
         d(i)=i
      end do

      open  (3,file='a',form='unformatted')
      write (3) a,b,c,d,e
      rewind 3
      read  (3) a,b,c,d
      close (3)

      print *,d(1)

      end


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] silent data corruption in gfortran read statement

[jvdelisle at gcc dot gnu dot org]

------- Comment #4 from jvdelisle at gcc dot gnu dot org  2007-05-10 01:07 -------
I am regression testing the patch.


-- 

jvdelisle at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jvdelisle at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2007-05-09 19:18:26         |2007-05-10 01:07:10
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] silent data corruption in gfortran read statement

[jvdelisle at gcc dot gnu dot org]

------- Comment #5 from jvdelisle at gcc dot gnu dot org  2007-05-10 02:01 -------
Subject: Bug 31880

Author: jvdelisle
Date: Thu May 10 01:01:27 2007
New Revision: 124588

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=124588
Log:
2007-05-09  Jerry DeLisle  <jvdelisle@gcc.gnu.org>

        PR libfortran/31880
        * io/unix.c (fd_alloc_r_at): Fix calculation of physical offset.

Modified:
    trunk/libgfortran/ChangeLog
    trunk/libgfortran/io/unix.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] silent data corruption in gfortran read statement

[jvdelisle at gcc dot gnu dot org]

------- Comment #6 from jvdelisle at gcc dot gnu dot org  2007-05-10 02:10 -------
Subject: Bug 31880

Author: jvdelisle
Date: Thu May 10 01:09:57 2007
New Revision: 124590

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=124590
Log:
2007-05-09  Jerry DeLisle  <jvdelisle@gcc.gnu.org>

        PR libfortran/31880
        * gfortran.dg/unf_read_corrupted_2.f90: New test.

Added:
    trunk/gcc/testsuite/gfortran.dg/unf_read_corrupted_2.f90
Modified:
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] silent data corruption in gfortran read statement

[jvdelisle at gcc dot gnu dot org]

------- Comment #7 from jvdelisle at gcc dot gnu dot org  2007-05-10 02:14 -------
Russel, thanks for finding this and reporting it.  I assume you do not have
copyright assignment.  I committed the patch because it is very small and
simple.

Thanks much!


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] silent data corruption in gfortran read statement

[jvdelisle at gcc dot gnu dot org]

------- Comment #8 from jvdelisle at gcc dot gnu dot org  2007-05-10 04:22 -------
Subject: Bug 31880

Author: jvdelisle
Date: Thu May 10 03:22:40 2007
New Revision: 124591

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=124591
Log:
2007-05-09  Jerry DeLisle  <jvdelisle@gcc.gnu.org>

        PR libfortran/31880
        * gfortran.dg/unf_read_corrupted_2.f90: Fix test.

Modified:
    trunk/gcc/testsuite/gfortran.dg/unf_read_corrupted_2.f90


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] [4.2 only] silent data corruption in gfortran read statement

[roconnor at health dot usf dot edu]

------- Comment #9 from roconnor at health dot usf dot edu  2007-05-10 12:50 -------
(In reply to comment #7)
> Russel, thanks for finding this and reporting it.  I assume you do not have
> copyright assignment.  I committed the patch because it is very small and
> simple.
> 
You're welcome.  Thank you for the prompt response.
You're right about the copyright assignment.  But even with the test case, it
comes in under the FSF's 15-line threshold for legally significant.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] [4.2 only] silent data corruption in gfortran read statement

[patchapp at dberlin dot org]

------- Comment #10 from patchapp at dberlin dot org  2007-05-10 17:25 -------
Subject: Bug number PR31880

A patch for this bug has been added to the patch tracker.
The mailing list url for the patch is
http://gcc.gnu.org/ml/gcc-patches/2007-05/msg00728.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] [4.2 only] silent data corruption in gfortran read statement

[jvdelisle at gcc dot gnu dot org]

------- Comment #11 from jvdelisle at gcc dot gnu dot org  2007-05-11 01:34 -------
Subject: Bug 31880

Author: jvdelisle
Date: Fri May 11 00:34:41 2007
New Revision: 124609

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=124609
Log:
2007-05-10  Jerry DeLisle  <jvdelisle@gcc.gnu.org>

        PR libfortran/31880
        * io/unix.c (fd_alloc_r_at): Fix calculation of physical offset.

2007-05-10  Jerry DeLisle  <jvdelisle@gcc.gnu.org>

        PR libfortran/31880
        * gfortran.dg/unf_read_corrupted_2.f90: New test.

Added:
    branches/gcc-4_1-branch/gcc/testsuite/gfortran.dg/unf_read_corrupted_2.f90
Modified:
    branches/gcc-4_1-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_1-branch/libgfortran/ChangeLog
    branches/gcc-4_1-branch/libgfortran/io/unix.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] [4.2 only] silent data corruption in gfortran read statement

[tkoenig at gcc dot gnu dot org]

------- Comment #12 from tkoenig at gcc dot gnu dot org  2007-05-11 19:16 -------
This is a regression WRT g77.


-- 

tkoenig at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |19292
              nThis|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] [4.2 only] silent data corruption in gfortran read statement

[tkoenig at gcc dot gnu dot org]

------- Comment #13 from tkoenig at gcc dot gnu dot org  2007-05-11 19:19 -------
Mark, this bug is critical - silent data corruption upon read
is really, really bad.

I second Jerry's DeLisle's request for inclusion in 4.2.  This is a
regression versus g77, the fix is simple and safe.


-- 

tkoenig at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mark at codesourcery dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] [4.2 only] silent data corruption in gfortran read statement

[mark at codesourcery dot com]

------- Comment #14 from mark at codesourcery dot com  2007-05-11 19:45 -------
Subject: Re:  [4.2 only] silent data corruption in gfortran
 read statement

tkoenig at gcc dot gnu dot org wrote:

> I second Jerry's DeLisle's request for inclusion in 4.2.  This is a
> regression versus g77, the fix is simple and safe.

OK, please apply the patch to 4.2.

However, please note for future that a patch should never go on 4.1
before it has gone on 4.2: we want to be sure that new regressions are
not being introduced!


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] [4.2 only] silent data corruption in gfortran read statement

[jvdelisle at gcc dot gnu dot org]

------- Comment #15 from jvdelisle at gcc dot gnu dot org  2007-05-11 22:54 -------
Subject: Bug 31880

Author: jvdelisle
Date: Fri May 11 21:53:52 2007
New Revision: 124626

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=124626
Log:
2007-05-11  Jerry DeLisle  <jvdelisle@gcc.gnu.org>

        PR libfortran/31880
        * io/unix.c (fd_alloc_r_at): Fix calculation of physical offset.

Modified:
    branches/gcc-4_2-branch/libgfortran/ChangeLog
    branches/gcc-4_2-branch/libgfortran/io/unix.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] [4.2 only] silent data corruption in gfortran read statement

[jvdelisle at gcc dot gnu dot org]

------- Comment #16 from jvdelisle at gcc dot gnu dot org  2007-05-11 22:57 -------
Subject: Bug 31880

Author: jvdelisle
Date: Fri May 11 21:57:05 2007
New Revision: 124627

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=124627
Log:
2007-05-11  Jerry DeLisle  <jvdelisle@gcc.gnu.org>

        PR libfortran/31880
        * gfortran.dg/unf_read_corrupted_2.f90: New test.

Added:
    branches/gcc-4_2-branch/gcc/testsuite/gfortran.dg/unf_read_corrupted_2.f90
Modified:
    branches/gcc-4_2-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880

[Bug libfortran/31880] [4.2 only] silent data corruption in gfortran read statement

[jvdelisle at gcc dot gnu dot org]

------- Comment #17 from jvdelisle at gcc dot gnu dot org  2007-05-11 23:00 -------
Fixed on 4.2, Closing.  Sorry for the premature commit on 4.1.


-- 

jvdelisle at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31880