create table t1 (t time, unique(t)) engine=innodb;

insert into t1 values (null),(null);

alter ignore table t1 modify t text not null default '';

Thread 13 "one_connection" hit Breakpoint 2, 0x000055555935c880 in __ubsan::ScopedReport::~ScopedReport() ()

(gdb) bt

#0  0x000055555935c880 in __ubsan::ScopedReport::~ScopedReport() ()

#1  0x00005555593614cb in handlePointerOverflowImpl(__ubsan::PointerOverflowData*, unsigned long, unsigned long, __ubsan::ReportOptions) ()

#2  0x0000555559361044 in __ubsan_handle_pointer_overflow ()

#3  0x000055555d8c7c4d in my_uca_scanner_next_utf8mb4 (scanner=0x7bffdcfa9e70, param=0x7bffdcfa9ec0) at /source/strings/ctype-uca-scanner_next.inl:84

#4  0x000055555d8cb785 in my_uca_strnncollsp_onelevel_utf8mb4 (cs=0x7e0ff61f9cb0, level=0x5555628892d0 <my_uca1400_info_tailored+8944>, s=0x7e8ff6370280 '\276' <repeats 200 times>..., 

    slen=0, t=0x0, tlen=0) at /source/strings/ctype-uca.inl:235

#5  0x000055555d88276a in my_uca_strnncollsp_utf8mb4 (cs=0x7e0ff61f9cb0, s=0x7e8ff6370280 '\276' <repeats 200 times>..., slen=0, t=0x0, tlen=0) at /source/strings/ctype-uca.inl:280

#6  0x000055555b0de008 in charset_info_st::strnncollsp (this=0x7e0ff61f9cb0, a=0x7e8ff6370280 '\276' <repeats 200 times>..., alen=0, b=0x0, blen=0) at /source/include/m_ctype.h:1102

#7  0x000055555b0a24f0 in Field_blob::cmp (this=0x7e4ff63c5b18, a=0x7e8ff6370280 '\276' <repeats 200 times>..., a_length=0, b=0x0, b_length=0) at /source/sql/field.cc:9019

#8  0x000055555b0a291e in Field_blob::cmp (this=0x7e4ff63c5b18, a_ptr=0x7e4ff63c5a20 "", b_ptr=0x7e4ff63c69b8 "") at /source/sql/field.cc:9029

#9  0x000055555a51dd6d in Field::cmp_offset (this=0x7e4ff63c5b18, row_offset=3992) at /source/sql/field.h:1355

#10 0x000055555b1d1eea in handler::check_duplicate_long_entry_key (this=0x7e4ff63c51b8, new_rec=0x7e4ff63c5a20 "", key_no=0) at /source/sql/handler.cc:7856

#11 0x000055555b1d5167 in handler::check_duplicate_long_entries (this=0x7e4ff63c51b8, new_rec=0x7e4ff63c5a20 "") at /source/sql/handler.cc:7915

#12 0x000055555b1db873 in handler::ha_write_row (this=0x7e4ff63c51b8, buf=0x7e4ff63c5a20 "") at /source/sql/handler.cc:8203

#13 0x000055555a21dd5a in copy_data_between_tables (thd=0x7eaff6368288, from=0x7d9ff628f308, to=0x7d9ff6298f08, ignore=true, order_num=0, order=0x0, copied=0x7bffdd4da160, 

    deleted=0x7bffdd4da180, alter_info=0x7bffdd33e320, alter_ctx=0x7bffdd4dae60, online=false, start_alter_id=0) at /source/sql/sql_table.cc:12769

#14 0x000055555a1e79ce in mysql_alter_table (thd=0x7eaff6368288, new_db=0x7eaff636cea0, new_name=0x7eaff636d308, create_info=0x7bffdd33e020, table_list=0x7ecff65c85f8, 

    recreate_info=0x7bffdd33ed00, alter_info=0x7bffdd33e320, order_num=0, order=0x0, ignore=true, if_exists=false) at /source/sql/sql_table.cc:11863

#15 0x000055555a5e0902 in Sql_cmd_alter_table::execute (this=0x7ecff65c8f20, thd=0x7eaff6368288) at /source/sql/sql_alter.cc:701

#16 0x0000555559be571c in mysql_execute_command (thd=0x7eaff6368288, is_called_from_prepared_stmt=false) at /source/sql/sql_parse.cc:5886

#17 0x0000555559b8f585 in mysql_parse (thd=0x7eaff6368288, rawbuf=0x7ecff65c84a8 "alter ignore table t1 modify t text not null default ''", length=55, parser_state=0x7bffdd4627b0)

    at /source/sql/sql_parse.cc:7915

#18 0x0000555559b7e076 in dispatch_command (command=COM_QUERY, thd=0x7eaff6368288, packet=0x7e8ff6320289 "alter ignore table t1 modify t text not null default ''", packet_length=55, 

    blocking=true) at /source/sql/sql_parse.cc:1902

#19 0x0000555559b94854 in do_command (thd=0x7eaff6368288, blocking=true) at /source/sql/sql_parse.cc:1415

#20 0x000055555a5a5cb4 in do_handle_one_connection (connect=0x7d0ff6213ec8, put_in_cache=true) at /source/sql/sql_connect.cc:1415

#21 0x000055555a5a4ff7 in handle_one_connection (arg=0x7d0ff6213ec8) at /source/sql/sql_connect.cc:1327

#22 0x000055555931c5d7 in asan_thread_start(void*) ()

#23 0x00007ffff742d1c4 in ?? () from /lib/x86_64-linux-gnu/libc.so.6

#24 0x00007ffff74ad85c in ?? () from /lib/x86_64-linux-gnu/libc.so.6

(gdb) frame 3

#3  0x000055555d8c7c4d in my_uca_scanner_next_utf8mb4 (scanner=0x7bffdcfa9e70, param=0x7bffdcfa9ec0) at /source/strings/ctype-uca-scanner_next.inl:84

84	    if (scanner->sbeg + 1 < scanner->send)

(gdb) p *scanner

$1 = {wbeg = 0x55555e89b9c0 <nochar>, sbeg = 0x0, send = 0x0, implicit = {0, 0}, page = 0, code = 0}

(gdb) up

#4  0x000055555d8cb785 in my_uca_strnncollsp_onelevel_utf8mb4 (cs=0x7e0ff61f9cb0, level=0x5555628892d0 <my_uca1400_info_tailored+8944>, s=0x7e8ff6370280 '\276' <repeats 200 times>..., 

    slen=0, t=0x0, tlen=0) at /source/strings/ctype-uca.inl:235

235	    t_res= MY_FUNCTION_NAME(scanner_next)(&tscanner, &param);

(gdb) up

#5  0x000055555d88276a in my_uca_strnncollsp_utf8mb4 (cs=0x7e0ff61f9cb0, s=0x7e8ff6370280 '\276' <repeats 200 times>..., slen=0, t=0x0, tlen=0) at /source/strings/ctype-uca.inl:280

280	  return MY_FUNCTION_NAME(strnncollsp_onelevel)(cs, &cs->uca->level[0],

(gdb) up

#6  0x000055555b0de008 in charset_info_st::strnncollsp (this=0x7e0ff61f9cb0, a=0x7e8ff6370280 '\276' <repeats 200 times>..., alen=0, b=0x0, blen=0) at /source/include/m_ctype.h:1102

1102	    return (coll->strnncollsp)(this, a, alen, b, blen);

(gdb) up

#7  0x000055555b0a24f0 in Field_blob::cmp (this=0x7e4ff63c5b18, a=0x7e8ff6370280 '\276' <repeats 200 times>..., a_length=0, b=0x0, b_length=0) at /source/sql/field.cc:9019

9019	  return field_charset()->strnncollsp(a, a_length, b, b_length);

(gdb) up

#8  0x000055555b0a291e in Field_blob::cmp (this=0x7e4ff63c5b18, a_ptr=0x7e4ff63c5a20 "", b_ptr=0x7e4ff63c69b8 "") at /source/sql/field.cc:9029

9029	  return cmp(blob1, (uint32)a_len, blob2, (uint32)b_len);

(gdb) info locals

blob1 = 0x7e8ff6370280 '\276' <repeats 200 times>...

blob2 = 0x0

a_len = 0

b_len = 0