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Re: Crash free()ing unallocated memory.

On Wed, Nov 5, 2008 at 7:03 PM, Paul Pluzhnikov <> wrote:

> I just debugged a crash, where gdb-py tries to free builtin type :-(

For some definition of debugged.

The bad free() appears to be a side effect, the real cause appears
to be reading free()d memory earlier. Here is what Valgrind has to
say about this:

==23804== Invalid read of size 4
==23804==    at 0x6E0C36: PyObject_Free ../../Objects/obmalloc.c:735
==23804==    by 0x713778: PyEval_EvalFrame ../../Python/ceval.c:1563
==23804==    by 0x716EB3: PyEval_EvalCodeEx ../../Python/ceval.c:2741
==23804==    by 0x7645E2: function_call ../../Objects/funcobject.c:548
==23804==    by 0x6BD6D6: PyObject_CallFunctionObjArgs
==23804==    by 0x45B3FF: pretty_print_one_value ../../gdb/python/python.c:792
==23804==    by 0x45B61C: apply_val_pretty_printer ../../gdb/python/python.c:865
==23804==    by 0x4A39AC: val_print ../../gdb/valprint.c:240
==23804==    by 0x56BA3F: cp_print_value_fields ../../gdb/cp-valprint.c:293
==23804==    by 0x56A32B: c_val_print ../../gdb/c-valprint.c:343
==23804==    by 0x4A3A5F: val_print ../../gdb/valprint.c:255
==23804==    by 0x56BA3F: cp_print_value_fields ../../gdb/cp-valprint.c:293
==23804==  Address 0x1068f020 is 40 bytes inside a block of size 141 free'd
==23804==    at 0x4C1CC8E: free vg_replace_malloc.c:337
==23804==    by 0x40B2E5: xfree ../../gdb/utils.c:1082
==23804==    by 0x4FE722: start_subfile ../../gdb/buildsym.c:550
==23804==    by 0x51CB08: dwarf2_start_subfile ../../gdb/dwarf2read.c:7293
==23804==    by 0x51C076: dwarf_decode_lines ../../gdb/dwarf2read.c:6994
==23804==    by 0x5134F8: read_file_scope ../../gdb/dwarf2read.c:2947
==23804==    by 0x512F3C: process_die ../../gdb/dwarf2read.c:2735
==23804==    by 0x512E40: process_full_comp_unit ../../gdb/dwarf2read.c:2702
==23804==    by 0x5128B7: process_queue ../../gdb/dwarf2read.c:2501
==23804==    by 0x512ADB: psymtab_to_symtab_1 ../../gdb/dwarf2read.c:2581
==23804==    by 0x512790: dwarf2_psymtab_to_symtab ../../gdb/dwarf2read.c:2454
==23804==    by 0x4B3101: psymtab_to_symtab ../../gdb/symfile.c:291

Does this ring any bells?

Unfortunately, I can seem to be able to construct a reduced test case :[

Paul Pluzhnikov

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