[Bug gdb/14290] New: gdb_bfd_unref frees an already freed memory block

["johnw at boostpro dot com" <sourceware-bugzilla@sourceware.org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14290

             Bug #: 14290
           Summary: gdb_bfd_unref frees an already freed memory block
           Product: gdb
           Version: 7.4
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
        AssignedTo: unassigned@sourceware.org
        ReportedBy: johnw@boostpro.com
    Classification: Unclassified


In gdb_bfd_unref, objfiles.c, the last lines in that function are:

    name = bfd_get_filename (abfd);
    gdb_bfd_close_or_warn (abfd);
    xfree (name);

The memory checker on OS X aborts gdb because xfree here is freeing a memory
block that was already freed elsewhere.

Reproducing this on OS X is trivial:

  1. Build GDB (with either gcc or clang)
  2. Code sign it:

     codesign -s gdb-cert gdb

  3. Use this gdb to debug any executable (including just "hello world")
  4. Run the program with "run"
  5. Run it again with "run".

You should see this:

    (XXXXX) malloc: *** error for object 0x10045b570: pointer being freed was
not allocated
*** set a breakpoint in malloc_error_break to debug

Here is the stack trace at the point of error:

Breakpoint 1, 0x00007fff8c8786c0 in malloc_error_break () from i386:x86-64
(gdb) bt
#0  0x00007fff8c8786c0 in malloc_error_break () from i386:x86-64
#1  0x00007fff8c878805 in free () from i386:x86-64
#2  0x00000001002ef4d3 in xfree (ptr=0x10045b570) at
./common/common-utils.c:107
#3  0x00000001001d6d12 in gdb_bfd_unref (abfd=0x103531440) at objfiles.c:1557
#4  0x00000001001d69b8 in free_objfile (objfile=0x1076cca00) at objfiles.c:597
#5  0x00000001001d7c98 in objfile_purge_solibs () at objfiles.c:986
#6  0x0000000100022ec9 in no_shared_libraries (ignored=0x0, from_tty=1) at
solib.c:1205
#7  0x00000001001c1677 in target_pre_inferior (from_tty=1) at target.c:2479
#8  0x000000010016d282 in run_command_1 (args=0x0, from_tty=1,
tbreak_at_main=0) at infcmd.c:516
#9  0x000000010016cb50 in run_command (args=0x0, from_tty=1) at infcmd.c:620
#10 0x0000000100069e3e in do_cfunc (c=0x100a40390, args=0x0, from_tty=1) at
./cli/cli-decode.c:67
#11 0x000000010006decc in cmd_func (cmd=0x100a40390, args=0x0, from_tty=1)
    at ./cli/cli-decode.c:1810
#12 0x00000001002b03e9 in execute_command (p=0x100a0a213 "", from_tty=1) at
top.c:441
#13 0x0000000100199ed9 in command_handler (command=0x100a0a210 "") at
event-top.c:435
#14 0x0000000100199d74 in command_line_handler (rl=0x10353a5b0 "") at
event-top.c:636
#15 0x0000000100314b7a in rl_callback_read_char () at callback.c:220
#16 0x0000000100199561 in rl_callback_read_char_wrapper (client_data=0x0) at
event-top.c:169
---Type <return> to continue, or q <return> to quit---
#17 0x0000000100198bca in stdin_event_handler (error=0, client_data=0x0) at
event-top.c:375
#18 0x00000001001984f9 in handle_file_event (data=...) at event-loop.c:827
#19 0x00000001001968bc in process_event () at event-loop.c:401
#20 0x0000000100196781 in gdb_do_one_event () at event-loop.c:465
#21 0x00000001001970ac in start_event_loop () at event-loop.c:490
#22 0x00000001001985d8 in cli_command_loop () at event-top.c:182
#23 0x000000010018e106 in current_interp_command_loop () at interps.c:309
#24 0x00000001001903de in captured_command_loop (data=0x0) at ./main.c:232
#25 0x000000010018d0c5 in catch_errors (func=0x1001903c0
<captured_command_loop>, func_args=0x0, 
    errstring=0x10040efea "", mask=6) at exceptions.c:502
#26 0x000000010018fe7e in captured_main (data=0x7fff5fbff5a0) at ./main.c:942
#27 0x000000010018d0c5 in catch_errors (func=0x10018ea70 <captured_main>, 
    func_args=0x7fff5fbff5a0, errstring=0x10040efea "", mask=6) at
exceptions.c:502
#28 0x000000010018ea5d in gdb_main (args=0x7fff5fbff5a0) at ./main.c:951
#29 0x0000000100000dbc in main (argc=1, argv=0x7fff5fbff5f8) at gdb.c:34

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