This is a standalone bug report for issue noticed in comment #25 of bug #629640.

Non-affected version: gdbm-1.8.0-36.el6
Affected version: gdbm-1.8.0-37.el6

After upgrading to gdbm-1.8.0-37.el6, this Perl code changed behaviour on x86_64:

$ cat gdbmfix 
#!/usr/bin/perl
use strict;
use warnings;
use GDBM_File;

unlink <Op.dbmx*>;
my %h;
tie(%h, 'GDBM_File', 'Op.dbmx', &GDBM_WRCREAT, 0640)
        or die "Initialization failed";
$h{'goner1'} = 'snork';
untie(%h);

$ ./gdbmfix 
gdbm store returned -1, errno 0, key "goner1" at ./gdbmfix line 10.

The failed line 10 is the "$h{'goner1'} = 'snork';" line. I debugged the gdbm library and the -1 comes from this check at the very beginning of gdbm_store():

  /* First check to make sure this guy is a writer. */
  if (dbf->read_write != GDBM_WRITER)
    {
      gdbm_errno = GDBM_READER_CANT_STORE;
      return -1;
    }

Debugger show that the dbf->read_write holds value 2 while GDBM_WRITER macro is declared as 1.

It looks like the gdbm_open() does not set the database handle is opened for writing:

When calling gdbm_open():

Breakpoint 1, gdbm_open (file=0x63f1f0 "Op.dbmx", block_size=0, flags=2, mode=416, fatal_func=0x7ffff7d25420 <Perl_croak_nocontext>) at gdbmopen.c:76

When leaving the gdbm_open():

Breakpoint 2, gdbm_open (file=0x63f1f0 "Op.dbmx", block_size=0, flags=2, mode=416, fatal_func=0x7ffff7d25420 <Perl_croak_nocontext>) at gdbmopen.c:398
398       return dbf;
(gdb) p *dbf
$6 = {name = 0x62d090 "Op.dbmx", read_write = 2, fast_write = 1, central_free = 0, coalesce_blocks = 0, file_locking = 1, fatal_err = 0x7ffff7d25420 <Perl_croak_nocontext>, desc = 7, 
  header = 0x62a8f0, dir = 0x69b720, bucket_cache = 0x0, cache_size = 0, last_read = -1, bucket = 0x0, bucket_dir = 0, cache_entry = 0x0, header_changed = 0 '\000', 
  directory_changed = 0 '\000', bucket_changed = 0 '\000', second_changed = 0 '\000'}

The flags=2 is GDBM_WRCREAT which corresponds to the Perl code.

This is caused by the last hunk of the gdbm patch introduced in gdbm-1.8.0-37.el6:

diff -up gdbm-1.8.0/gdbmopen.c.gdbmopen gdbm-1.8.0/gdbmopen.c
--- gdbm-1.8.0/gdbmopen.c.gdbmopen  2012-06-12 10:08:02.853499099 +0200
+++ gdbm-1.8.0/gdbmopen.c   2012-06-12 10:08:13.620769745 +0200
@@ -129,19 +129,17 @@ gdbm_open (file, block_size, flags, mode
    dbf->desc = open (dbf->name, O_RDONLY, 0);
    break;

-      case GDBM_OPENMASK:
+      case GDBM_WRITER:
    dbf->desc = open (dbf->name, O_RDWR, 0);
    break;

       case GDBM_NEWDB:
    dbf->desc = open (dbf->name, O_RDWR|O_CREAT, mode);
-   flags = GDBM_WRITER;
    need_trunc = TRUE;
    break;

       default:
    dbf->desc = open (dbf->name, O_RDWR|O_CREAT, mode);
-   flags = GDBM_WRITER; ← THIS IS MISSING
    break;