Re: [PATCH] Fix "nosharedlibrary + continue + shared lib event" crash

[Pedro Alves <palves at redhat dot com>]

On 4/11/19 3:49 AM, Simon Marchi wrote:
> On 2019-04-09 9:14 a.m., Pedro Alves wrote:
>> GDB misbehaves if you run the "nosharelibrary" command, continue
>> execution, and then the program hits the shared library event
>> breakpoint.  On my system it aborts like this:
>>
>>  (gdb) nosharedlibrary
>>  (gdb) c
>>  Continuing.
>>  pure virtual method called
>>  terminate called without an active exception
>>  Aborted (core dumped)
>>
>> Though it's really undefined behavior territory, caused by deferencing
>> a dangling solib event probe pointer.
>>
>> I've observed this by running "nosharedlibrary" when stopped at the
>> entry point, but it should happen at any other point, if the program
>> does a dlopen/dlclose after.
>>
>> The fix is to discard an objfile's probes from the svr4 probes table
>> when an objfile is about to be released.
>>
>> New test included, works with both native and gdbserver testing.
>>
>> Valgrind log:
>>
>>  (gdb) starti
>>  (gdb) nosharedlibrary
>>  (gdb) c
>>  Continuing.
>>  ==24895== Invalid read of size 8
>>  ==24895==    at 0x89E5FB: solib_event_probe_action(probe_and_action*) (solib-svr4.c:1735)
>>  ==24895==    by 0x89E95A: svr4_handle_solib_event() (solib-svr4.c:1872)
>>  ==24895==    by 0x8A7198: handle_solib_event() (solib.c:1274)
>>  ==24895==    by 0x4E3407: bpstat_stop_status(address_space const*, unsigned long, thread_info*, target_waitstatus const*, bpstats*) (breakpoint.c:5407)
>>  ==24895==    by 0x721F41: handle_signal_stop(execution_control_state*) (infrun.c:5685)
>>  ==24895==    by 0x720B11: handle_inferior_event(execution_control_state*) (infrun.c:5129)
>>  ==24895==    by 0x71DD93: fetch_inferior_event(void*) (infrun.c:3748)
>>  ==24895==    by 0x7059C3: inferior_event_handler(inferior_event_type, void*) (inf-loop.c:43)
>>  ==24895==    by 0x874DF0: remote_async_serial_handler(serial*, void*) (remote.c:14039)
>>  ==24895==    by 0x894101: run_async_handler_and_reschedule(serial*) (ser-base.c:137)
>>  ==24895==    by 0x8941E6: fd_event(int, void*) (ser-base.c:188)
>>  ==24895==    by 0x67AFEF: handle_file_event(file_handler*, int) (event-loop.c:732)
>>  ==24895==  Address 0x18b63860 is 0 bytes inside a block of size 136 free'd
>>  ==24895==    at 0x4C2E616: operator delete(void*, unsigned long) (vg_replace_malloc.c:585)
>>  ==24895==    by 0x8C6A12: stap_probe::~stap_probe() (stap-probe.c:124)
>>  ==24895==    by 0x66F7DB: probe_key_free(bfd*, void*) (elfread.c:1382)
>>  ==24895==    by 0x69B705: bfdregistry_callback_adaptor(void (*)(registry_container*, void*), registry_container*, void*) (gdb_bfd.c:131)
>>  ==24895==    by 0x855A57: registry_clear_data(registry_data_registry*, void (*)(void (*)(registry_container*, void*), registry_container*, void*), registry_container*, registry_fields*) (registry.c:79)
>>  ==24895==    by 0x855B01: registry_container_free_data(registry_data_registry*, void (*)(void (*)(registry_container*, void*), registry_container*, void*), registry_container*, registry_fields*) (registry.c:92)
>>  ==24895==    by 0x69B783: bfd_free_data(bfd*) (gdb_bfd.c:131)
>>  ==24895==    by 0x69C4BA: gdb_bfd_unref(bfd*) (gdb_bfd.c:609)
>>  ==24895==    by 0x7CC33F: objfile::~objfile() (objfiles.c:651)
>>  ==24895==    by 0x7CD559: objfile_purge_solibs() (objfiles.c:1021)
>>  ==24895==    by 0x8A7132: no_shared_libraries(char const*, int) (solib.c:1252)
>>  ==24895==    by 0x548E3D: do_const_cfunc(cmd_list_element*, char const*, int) (cli-decode.c:106)
>>  ==24895==  Block was alloc'd at
>>  ==24895==    at 0x4C2D42A: operator new(unsigned long) (vg_replace_malloc.c:334)
>>  ==24895==    by 0x8C527C: handle_stap_probe(objfile*, sdt_note*, std::vector<probe*, std::allocator<probe*> >*, unsigned long) (stap-probe.c:1561)
>>  ==24895==    by 0x8C5535: stap_static_probe_ops::get_probes(std::vector<probe*, std::allocator<probe*> >*, objfile*) const (stap-probe.c:1656)
>>  ==24895==    by 0x66F71B: elf_get_probes(objfile*) (elfread.c:1365)
>>  ==24895==    by 0x7EDD85: find_probes_in_objfile(objfile*, char const*, char const*) (probe.c:227)
>>  ==24895==    by 0x4DF382: create_longjmp_master_breakpoint() (breakpoint.c:3275)
>>  ==24895==    by 0x4F6562: breakpoint_re_set() (breakpoint.c:13828)
>>  ==24895==    by 0x8A66AA: solib_add(char const*, int, int) (solib.c:1010)
>>  ==24895==    by 0x89F7C6: enable_break(svr4_info*, int) (solib-svr4.c:2360)
>>  ==24895==    by 0x8A104C: svr4_solib_create_inferior_hook(int) (solib-svr4.c:2992)
>>  ==24895==    by 0x8A70B9: solib_create_inferior_hook(int) (solib.c:1215)
>>  ==24895==    by 0x70C073: post_create_inferior(target_ops*, int) (infcmd.c:467)
>>  ==24895==
>>  pure virtual method called
>>  terminate called without an active exception
>>  ==24895==
>>  ==24895== Process terminating with default action of signal 6 (SIGABRT): dumping core
>>  ==24895==    at 0x7CF3750: raise (raise.c:51)
>>  ==24895==    by 0x7CF4D30: abort (abort.c:79)
>>  ==24895==    by 0xB008F4: __gnu_cxx::__verbose_terminate_handler() (in build/gdb/gdb)
>>  ==24895==    by 0xAFF845: __cxxabiv1::__terminate(void (*)()) (in build/gdb/gdb)
>>  ==24895==    by 0xAFF890: std::terminate() (in build/gdb/gdb)
>>  ==24895==    by 0xAFF95E: __cxa_pure_virtual (in build/gdb/gdb)
>>  ==24895==    by 0x89E610: solib_event_probe_action(probe_and_action*) (solib-svr4.c:1735)
>>  ==24895==    by 0x89E95A: svr4_handle_solib_event() (solib-svr4.c:1872)
>>  ==24895==    by 0x8A7198: handle_solib_event() (solib.c:1274)
>>  ==24895==    by 0x4E3407: bpstat_stop_status(address_space const*, unsigned long, thread_info*, target_waitstatus const*, bpstats*) (breakpoint.c:5407)
>>  ==24895==    by 0x721F41: handle_signal_stop(execution_control_state*) (infrun.c:5685)
>>  ==24895==    by 0x720B11: handle_inferior_event(execution_control_state*) (infrun.c:5129)
>>  ==24895==
>>
>> Note, this little bit in the patch is just a cleanup that I noticed:
>>
>>  -  lookup.prob = prob;
>>     lookup.address = address;
>>
>> That line isn't necessary because hashing/comparison only looks at the
>> address.
> 
> I am not able to reproduce the problem, and the test doesn't fail here, without
> the rest of the patch applied.  I think it's because on my system gdb doesn't use
> the probe based interface.
> 
> Anyhow, the fix makes sense.  Since the probe is deleted on objfile destruction, the
> corresponding probe_and_action structures should too.

Thanks for the review.  I've pushed it in now, with an additional 

 "On systems that use the probes-based solib interface, "

at the beginning of the commit log.

Thanks,
Pedro Alves