[Bug libfortran/65563] New: Segfault on reopening fort.xxx file with explicit name

[tkoenig at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65563

            Bug ID: 65563
           Summary: Segfault on reopening fort.xxx file with explicit name
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libfortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tkoenig at gcc dot gnu.org

This is inspired by
https://stackoverflow.com/questions/29238857/fortran-error-about-eof-marker/
,but is slightly different.

This segfaults:

  variable_1 = 0
  open(345,iostat=ios, form='unformatted')
  read(345, err=37, end=37) variable_1
  close(345)
  go to 38
37 continue
38 continue
  open(522, file="fort.345", form='unformatted')
  write(522) variable_1
  rewind(522)
  close(522)
end program

Backtrace:

#0  0x00007ffff778d42a in strlen () from /lib64/libc.so.6
#1  0x00007ffff778d14e in strdup () from /lib64/libc.so.6
#2  0x00007ffff7ba1eec in _gfortrani_filename_from_unit (n=<optimized out>)
    at ../../../trunk/libgfortran/io/unit.c:833
#3  0x00007ffff7ad83af in _gfortrani_show_locus (cmp=0x7fffffffd7f0)
    at ../../../trunk/libgfortran/runtime/error.c:266
#4  0x00007ffff7ad8990 in _gfortrani_generate_error
(cmp=cmp@entry=0x7fffffffd7f0, 
    family=family@entry=5004, message=0x7ffff7bb8b60 "File already opened in
another unit", 
    message@entry=0x0) at ../../../trunk/libgfortran/runtime/error.c:561
#5  0x00007ffff7b9a1f4 in _gfortrani_new_unit (opp=opp@entry=0x7fffffffd7f0,
u=u@entry=0x6083e0, 
    flags=flags@entry=0x7fffffffd790) at
../../../trunk/libgfortran/io/open.c:493
#6  0x00007ffff7b9a6ee in already_open (flags=<optimized out>, u=<optimized
out>, opp=<optimized out>)
    at ../../../trunk/libgfortran/io/open.c:694