Fix "nosharedlibrary + continue + shared lib event" crash

Fix "nosharedlibrary + continue + shared lib event" crash

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

gdb/ChangeLog:
2019-04-22  Pedro Alves  <palves@redhat.com>

	* solib-svr4.c (svr4_free_objfile_observer): New.
	(probe_and_action::objfile): New field.
	(probes_table_htab_remove_objfile_probes)
	(probes_table_remove_objfile_probes): New functions.
	(register_solib_event_probe): Add 'objfile' parameter.  Store it
	in the new probe_and_action.  Don't store the probe in 'lookup'.
	(svr4_create_probe_breakpoints): Pass objfile to
	register_solib_event_probe.
	(_initialize_svr4_solib): Register a free_objfile observer.

gdb/testsuite/ChangeLog:
2019-04-22  Pedro Alves  <palves@redhat.com>

	* gdb.base/solib-probes-nosharedlibrary.c,
	gdb.base/solib-probes-nosharedlibrary.exp: New files.