[Bug tui/30823] New: [gdb/tui] segfault in tui_find_disassembly_address

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30823

            Bug ID: 30823
           Summary: [gdb/tui] segfault in tui_find_disassembly_address
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: tui
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

I was walking through
outputs/gdb.threads/next-fork-other-thread/next-fork-other-thread-fork (build
with target board unix/-m32), using TUI layout asm, first setting a breakpoint
at fork and the running, then doing nexti a lot when hitting the breakpoints in
the various threads.

I ran into a segfault:
...
(gdb) bt
#0  0x00007fe36c6ad76b in raise () from /lib64/libpthread.so.0
#1  0x000000000078ed99 in handle_fatal_signal (sig=11) at
/data/vries/gdb/src/gdb/event-top.c:912
#2  0x000000000078ee21 in handle_sigsegv (sig=11) at
/data/vries/gdb/src/gdb/event-top.c:962
#3  <signal handler called>
#4  0x0000000000c5e7a4 in tui_find_disassembly_address (gdbarch=0x45110a0,
pc=4158011920, from=-6)
    at /data/vries/gdb/src/gdb/tui/tui-disasm.c:247
#5  0x0000000000c5f0c3 in tui_get_low_disassembly_address (gdbarch=0x45110a0,
low=4158011920, 
    pc=4158011920) at /data/vries/gdb/src/gdb/tui/tui-disasm.c:439
#6  0x0000000000c5f32e in tui_disasm_window::maybe_update (this=0x42ecdb0,
fi=..., sal=...)
    at /data/vries/gdb/src/gdb/tui/tui-disasm.c:500
#7  0x0000000000c7fc83 in tui_show_frame_info (fi=...)
    at /data/vries/gdb/src/gdb/tui/tui-stack.c:284
#8  0x0000000000c6140f in tui_refresh_frame_and_register_information ()
    at /data/vries/gdb/src/gdb/tui/tui-hooks.c:136
#9  0x0000000000c61618 in tui_before_prompt (
    current_gdb_prompt=0x293ced0 <top_prompt+16> "(gdb) ")
    at /data/vries/gdb/src/gdb/tui/tui-hooks.c:185
#10 0x0000000000797fa5 in std::_Function_handler<void (char const*), void
(*)(char const*)>::_M_invoke(std::_Any_data const&, char const*&&)
(__functor=..., 
    __args#0=@0x7fffc6b93e00: 0x293ced0 <top_prompt+16> "(gdb) ")
    at /usr/include/c++/7/bits/std_function.h:316
#11 0x000000000078fcc1 in std::function<void (char const*)>::operator()(char
const*) const (
    this=0x4950e10, __args#0=0x293ced0 <top_prompt+16> "(gdb) ")
    at /usr/include/c++/7/bits/std_function.h:706
#12 0x000000000078fa96 in gdb::observers::observable<char const*>::notify (
    this=0x2938560 <gdb::observers::before_prompt>, args#0=0x293ced0
<top_prompt+16> "(gdb) ")
    at /data/vries/gdb/src/gdb/../gdbsupport/observable.h:166
#13 0x000000000078e20d in top_level_prompt () at
/data/vries/gdb/src/gdb/event-top.c:474
#14 0x000000000078e110 in display_gdb_prompt (new_prompt=0x0)
    at /data/vries/gdb/src/gdb/event-top.c:441
#15 0x00000000005fe6c8 in cli_interp_base::on_sync_execution_done
(this=0x43ddfc0)
    at /data/vries/gdb/src/gdb/cli/cli-interp.c:149
#16 0x000000000085cb32 in check_curr_ui_sync_execution_done ()
    at /data/vries/gdb/src/gdb/infrun.c:4285
#17 0x000000000085cb6e in all_uis_check_sync_execution_done ()
    at /data/vries/gdb/src/gdb/infrun.c:4297
#18 0x000000000085d334 in fetch_inferior_event () at
/data/vries/gdb/src/gdb/infrun.c:4563
#19 0x000000000083ace6 in inferior_event_handler (event_type=INF_REG_EVENT)
    at /data/vries/gdb/src/gdb/inf-loop.c:42
#20 0x000000000086b136 in infrun_async_inferior_event_handler (data=0x0)
    at /data/vries/gdb/src/gdb/infrun.c:9836
#21 0x000000000052ad74 in check_async_event_handlers ()
    at /data/vries/gdb/src/gdb/async-event.c:338
#22 0x000000000149b938 in gdb_do_one_event (mstimeout=-1)
    at /data/vries/gdb/src/gdbsupport/event-loop.cc:221
#23 0x00000000008f5d37 in start_event_loop () at
/data/vries/gdb/src/gdb/main.c:412
#24 0x00000000008f5e91 in captured_command_loop () at
/data/vries/gdb/src/gdb/main.c:476
#25 0x00000000008f767d in captured_main (data=0x7fffc6b94540)
    at /data/vries/gdb/src/gdb/main.c:1320
#26 0x00000000008f7717 in gdb_main (args=0x7fffc6b94540) at
/data/vries/gdb/src/gdb/main.c:1339
#27 0x0000000000415f53 in main (argc=10, argv=0x7fffc6b94658) at
/data/vries/gdb/src/gdb/gdb.c:39
(gdb) 
...

The problem seems to be here:
...
(gdb) down
#4  0x0000000000c5e7a4 in tui_find_disassembly_address (gdbarch=0x45110a0,
pc=4158011920, from=-6)
    at /data/vries/gdb/src/gdb/tui/tui-disasm.c:247
247               last_addr = asm_lines.back ().addr;
(gdb) p asm_lines.back ()
You can't do that without a process to debug.
(gdb) p asm_lines
$3 = {<std::_Vector_base<tui_asm_line, std::allocator<tui_asm_line> >> = {
    _M_impl = {<std::allocator<tui_asm_line>> =
{<__gnu_cxx::new_allocator<tui_asm_line>> = {<No data fields>}, <No data
fields>}, _M_start = 0x0, _M_finish = 0x0, 
      _M_end_of_storage = 0x0}}, <No data fields>}
...

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