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Date: Sun, 07 Mar 2010 22:06:00 -0000
From: "stephan dot kramer at imperial dot ac dot uk" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Message-ID: <20100307220622.11354.stephan.kramer@imperial.ac.uk>
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Subject: [Bug fortran/11354] New: error in evaluating variable length fortran strings causes stalls
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The below simple test program was compiled with gfortran 4.4.1, -g. After
putting a breakpoint on the print line, the displayed frame looks as follows:

Breakpoint 1, print_string (string=Cannot access memory at address 0x80487eb
) at string.f90:11

I don't mind so much the string not being printed correctly (lots of things in
fortran aren't), but in particular for big executables this seems to cause huge
waiting times for the frame to be printed out (several minutes). This makes gdb
7.0 and 7.1 currently unusable for our project.

After a digging a little deeper, the cause seems to be the length of the string
not being picked up correctly from stack. Putting a breakpoint on valops.c (cvs
1.237 of the gdb_7_1-branch) on line 942 value_fetch_lazy(), the length of the
value it tries to read is some random big number. It then tries to read this
from the debugged process memory, and fails reaching the end which takes quite a
while for a large process.

The sample program:

program main
  implicit none
  
  call print_string("hello world")
    
  contains
  
  subroutine print_string(string)
    character(len=*):: string
    
    print *, string
    
  end subroutine print_string
end program main

-- 
           Summary: error in evaluating variable length fortran strings
                    causes stalls
           Product: gdb
           Version: 7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: fortran
        AssignedTo: unassigned at sourceware dot org
        ReportedBy: stephan dot kramer at imperial dot ac dot uk
                CC: gdb-prs at sourceware dot org


http://sourceware.org/bugzilla/show_bug.cgi?id=11354

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