[Bug fortran/100954] New: writing to a character opens unit -10

[Bug fortran/100954] New: writing to a character opens unit -10

[tacodog311 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100954

            Bug ID: 100954
           Summary: writing to a character opens unit -10
           Product: gcc
           Version: 7.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tacodog311 at gmail dot com
  Target Milestone: ---

Created attachment 50959
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50959&action=edit
save-temps output

The function "newunit" grabs unit -10 for its first choice.

Writing into a character string using "write(charstring,(I4.4)) ivalue" also
opens iounit -10.

After such a write, the "inquire" function will show the "newunit" file as
open, which means you can't check the open-ness of the original file. And
trying to close the reportedly open file unit it causes a seg fault.

String writes do not open unit -10 on gcc 7.2.0 and lower.  I see it on all
versions I've checked at 7.3 and higher up to ~10.2.

The code below runs without issue on intel compilers.




$ gfortran -v
Using built-in specs.
COLLECT_GCC=gfortran
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
7.5.0-3ubuntu1~18.04' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --program-suffix=-7
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie
--with-system-zlib --with-target-system-zlib --enable-objc-gc=auto
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04) 






Sample code:

program inquire
      implicit none
      logical opened
      character(len=256) filename
      character(len=4) charstring

      integer iounit, itmp, ierr

      filename='testfile'

      iounit=-10
      inquire(iounit, opened=opened,iostat=ierr)
      ! not open yet
      write(*,*) 'Unit',iounit,'open?',opened,ierr

      ! new unit grabs -10
      open(newunit=iounit,file=trim(filename) )
      write(*,*) 'Opened unit',iounit

      ! now -10 is open
      inquire(iounit, opened=opened,iostat=ierr)
      write(*,*) 'Unit',iounit,'open?',opened,ierr

      ! close it
      close(iounit)
      write(*,*) 'Closed unit',iounit

      ! now -10 is closed
      inquire(iounit, opened=opened,iostat=ierr)
      write(*,*) 'Unit',iounit,'open?',opened,ierr

      itmp=0
      write(charstring, '(I4.4)') itmp
      write(*,*) 'wrote into charstring ', trim(charstring)


      ! now -10 is reported as open again
      inquire(iounit, opened=opened,iostat=ierr)
      write(*,*) 'Unit',iounit,'open?',opened,ierr

      ! trying to close it seg faults
      if (opened) then
        close(iounit)
      endif

endprogram inquire





Sample output:

gfortran test.f90 -o test.x && ./test.x 
 Unit         -10 open? F           0
 Opened unit         -10
 Unit         -10 open? T           0
 Closed unit         -10
 Unit         -10 open? F           0
 wrote into charstring 0000
 Unit         -10 open? T           0

Program received signal SIGSEGV: Segmentation fault - invalid memory reference.





$ gfortran -v -save-temps test.f90 
Driving: gfortran -v -save-temps test.f90 -l gfortran -l m -shared-libgcc
Using built-in specs.
COLLECT_GCC=gfortran
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
7.5.0-3ubuntu1~18.04' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --program-suffix=-7
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie
--with-system-zlib --with-target-system-zlib --enable-objc-gc=auto
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/7/f951 test.f90 -quiet -dumpbase test.f90
-mtune=generic -march=x86-64 -auxbase test -version -fintrinsic-modules-path
/usr/lib/gcc/x86_64-linux-gnu/7/finclude -o test.s
GNU Fortran (Ubuntu 7.5.0-3ubuntu1~18.04) version 7.5.0 (x86_64-linux-gnu)
        compiled by GNU C version 7.5.0, GMP version 6.1.2, MPFR version 4.0.1,
MPC version 1.1.0, isl version isl-0.19-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU Fortran2008 (Ubuntu 7.5.0-3ubuntu1~18.04) version 7.5.0 (x86_64-linux-gnu)
        compiled by GNU C version 7.5.0, GMP version 6.1.2, MPFR version 4.0.1,
MPC version 1.1.0, isl version isl-0.19-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 as -v --64 -o test.o test.s
GNU assembler version 2.30 (x86_64-linux-gnu) using BFD version (GNU Binutils
for Ubuntu) 2.30
Reading specs from /usr/lib/gcc/x86_64-linux-gnu/7/libgfortran.spec
rename spec lib to liborig
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/7/collect2 -plugin
/usr/lib/gcc/x86_64-linux-gnu/7/liblto_plugin.so
-plugin-opt=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
-plugin-opt=-fresolution=test.res -plugin-opt=-pass-through=-lgcc_s
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lquadmath
-plugin-opt=-pass-through=-lm -plugin-opt=-pass-through=-lgcc_s
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc --build-id
--eh-frame-hdr -m elf_x86_64 --hash-style=gnu --as-needed -dynamic-linker
/lib64/ld-linux-x86-64.so.2 -pie -z now -z relro
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/Scrt1.o
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/crti.o
/usr/lib/gcc/x86_64-linux-gnu/7/crtbeginS.o -L/usr/lib/gcc/x86_64-linux-gnu/7
-L/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu
-L/usr/lib/gcc/x86_64-linux-gnu/7/../../../../lib -L/lib/x86_64-linux-gnu
-L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib
-L/usr/lib/gcc/x86_64-linux-gnu/7/../../.. test.o -lgfortran -lm -lgcc_s -lgcc
-lquadmath -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/usr/lib/gcc/x86_64-linux-gnu/7/crtendS.o
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/crtn.o
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'

[Bug fortran/100954] writing to a character opens unit -10

[kargl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100954

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kargl at gcc dot gnu.org

--- Comment #1 from kargl at gcc dot gnu.org ---
(In reply to Taco Jerkface from comment #0)
> Sample code:
> 
> program inquire
>       implicit none
>       logical opened
>       character(len=256) filename
>       character(len=4) charstring
> 
>       integer iounit, itmp, ierr
> 
>       filename='testfile'
> 
>       iounit=-10
>       inquire(iounit, opened=opened,iostat=ierr)
>       ! not open yet
>       write(*,*) 'Unit',iounit,'open?',opened,ierr

I believe the above is invalid Fortran.  Fortran 2018, pp. 216-218

  R1201 io-unit           is file-unit-number
  R1202 file-unit-number  is scalar-int-expr

  A unit is either an external unit or an internal unit. An external unit
  is used to refer to an external file and is specified by an asterisk or
  a file-unit-number. The value of file-unit-number shall be nonnegative,
  equal to one of the named constants INPUT_UNIT, OUTPUT_UNIT, or ERROR_UNIT
  of the intrinsic module ISO_FORTRAN_ENV (16.10.2), the unit argument of an
  active defined input/output procedure (12.6.4.8), or a NEWUNIT value
  (12.5.6.12).

In the above Fortran code, iounit is negative and it is not a NEWUNIT
value. There is some wiggle room, in that 

  All input/output statements are permitted to refer to units that exist.
  The CLOSE, INQUIRE, and WAIT statements are also permitted to refer to
  units that do not exist. No other input/output statement shall refer to
  a unit that does not exist.

Your code could have done 'inquire(unit=42, opened=opened,iostat=ierr)'
where 42 is nonnegative and refers to a unit that does not exist.  But,
iounit=-10 is negative and does not refer to a unit opened with NEWUNIT.
For NEWUNIT, the Fortran standard requires

  The variable is defined with a processor determined NEWUNIT value...

  A NEWUNIT value is a negative number, and shall not be equal to -1,
  any of the named constants ERROR_UNIT, INPUT_UNIT, or OUTPUT_UNIT from
  the intrinsic module ISO_FORTRAN_ENV (16.10.2), any value used by the
  processor for the unit argument to a defined input/output procedure,
  nor any previous NEWUNIT value that identifies a file that is connected.
  The unit identified by a NEWUNIT value shall not be preconnected.

So, the Fortran standard does not require -10 to be a NEWUNIT value.

> 
>       ! new unit grabs -10
>       open(newunit=iounit,file=trim(filename) )
>       write(*,*) 'Opened unit',iounit
> 
>       ! now -10 is open
>       inquire(iounit, opened=opened,iostat=ierr)
>       write(*,*) 'Unit',iounit,'open?',opened,ierr
> 
>       ! close it
>       close(iounit)
>       write(*,*) 'Closed unit',iounit

The above is conforming as it seems that gfortran has assigned -10
as the unit number via the NEWUNIT mechanism.  However, after the
close statement, there is no NEWUNIT value.

>       ! now -10 is closed
>       inquire(iounit, opened=opened,iostat=ierr)
>       write(*,*) 'Unit',iounit,'open?',opened,ierr

See above as I believe that this is invalid Fortran.

>       itmp=0
>       write(charstring, '(I4.4)') itmp
>       write(*,*) 'wrote into charstring ', trim(charstring)
> 
> 
>       ! now -10 is reported as open again
>       inquire(iounit, opened=opened,iostat=ierr)
>       write(*,*) 'Unit',iounit,'open?',opened,ierr

Invalid code can yield unexpected results.

>       ! trying to close it seg faults
>       if (opened) then
>         close(iounit)
>       endif
> 
> endprogram inquire

Of course, I could be wrong, so I'll leave this for other to pondered.

[Bug fortran/100954] writing to a character opens unit -10

[tacodog311 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100954

--- Comment #2 from Taco Jerkface <tacodog311 at gmail dot com> ---
Agreed.  A typical user will use unit=42, when manually picking unit numbers. 
However the bug remains for automatic, newunit unit numbers.

To reproduce:
1) Open a "newunit" file.
2) close file
3) write to character string
4) "newunit" file appears open, even though it has been closed.


A more concise version of the code would be:

program inquire
      implicit none
      logical opened
      character(len=256) filename
      character(len=4) charstring

      integer iounit, itmp, ierr

      filename='testfile'

      ! new unit grabs -10
      open(newunit=iounit,file=trim(filename) )
      write(*,*) 'Opened unit',iounit

      ! now -10 is open
      inquire(iounit, opened=opened,iostat=ierr)
      write(*,*) 'Unit',iounit,'open?',opened,ierr

      ! close it
      close(iounit)
      write(*,*) 'Closed unit',iounit

      ! now -10 is closed
      inquire(iounit, opened=opened,iostat=ierr)
      write(*,*) 'Unit',iounit,'open?',opened,ierr

      itmp=0
      write(charstring, '(I4.4)') itmp
      write(*,*) 'wrote into charstring ', trim(charstring)

      ! now -10 is reported as open again, but it is not
      inquire(iounit, opened=opened,iostat=ierr)
      write(*,*) 'Unit',iounit,'open?',opened,ierr

endprogram inquire

[Bug libfortran/100954] writing to a character opens unit -10

[anlauf at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100954

anlauf at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |anlauf at gcc dot gnu.org
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-10-01
          Component|fortran                     |libfortran

--- Comment #3 from anlauf at gcc dot gnu.org ---
This is possibly a bookkeeping issue.

Reduced testcase:

program inquire
  implicit none
  integer      :: iounit, ierr
  logical      :: opened
  character(4) :: c
! open(newunit=iounit,file="testfile")
  write(c,'(a)') "abcd"
  iounit = -10
  inquire(iounit, opened=opened,iostat=ierr)
  print *,iounit,'open?',opened,ierr
  iounit = -11
  inquire(iounit, opened=opened,iostat=ierr)
  print *,iounit,'open?',opened,ierr
endprogram inquire

This prints

         -10 open? T           0
         -11 open? F           0

but should print

         -10 open? F           0
         -11 open? F           0

Note that the start value -10 comes from unit.c:

#define NEWUNIT_START -10

If we uncomment before the internal write

  open(newunit=iounit,file="testfile")

then we'll find that units -10 and -11 are opened:

         -10 open? T           0
         -11 open? T           0

If we swap the open and internal write, then -11 is not opened:

         -10 open? T           0
         -11 open? F           0