Package: gdb
Version: 6.4.90-debian
The patches that debian-etch adds to gdb-6.4.90 make it SEGV if
thread_db.so doesn't contain all of the expected symbols (td_init,
td_ta_new, td_ta_map_id2thr, td_ta_map_lwp2thr etc).
Using a debug build of gdb-6.4.90-debian (built with `apt-get -b
source gdb') gives a core dump with the following backtrace:
#0 0x08093765 in check_for_thread_db () at
/home/gregjules/gdb-6.4.90.dfsg/gdb/linux-thread-db.c:676
676 printf_unfiltered (_("Using host libthread_db library
\"%s\".\n"),
(gdb) bt
#0 0x08093765 in check_for_thread_db () at
/home/gregjules/gdb-6.4.90.dfsg/gdb/linux-thread-db.c:676
#1 0x081a327b in inf_ptrace_him (pid=2684) at
/home/gregjules/gdb-6.4.90.dfsg/gdb/inf-ptrace.c:126
#2 0x081a3af9 in fork_inferior (
exec_file_arg=0x82fe030 ..., allargs=0x8334c68 "", env=0x82df708,
traceme_fun=0x81a2920 <inf_ptrace_me>, init_trace_fun=0x81a3220
<inf_ptrace_him>, pre_trace_fun=0,
shell_file_arg=0x0) at
/home/gregjules/gdb-6.4.90.dfsg/gdb/fork-child.c:396
#3 0x081a321d in inf_ptrace_create_inferior (
exec_file=0x82fe030 "...", allargs=0x8334c68 "", env=0x82df708,
from_tty=1) at /home/gregjules/gdb-6.4.90.dfsg/gdb/inf-ptrace.c:138
#4 0x0810c3ff in run_command_1 (args=0x0, from_tty=1,
tbreak_at_main=<value optimized out>) at
/home/gregjules/gdb-6.4.90.dfsg/gdb/infcmd.c:546
#5 0x0807f133 in execute_command (p=0x82be245 "", from_tty=1) at
/home/gregjules/gdb-6.4.90.dfsg/gdb/top.c:452
#6 0x0811ca1b in command_handler (command=0x82be240 "") at
/home/gregjules/gdb-6.4.90.dfsg/gdb/event-top.c:512
#7 0x0811d759 in command_line_handler (rl=0x830e858 "") at
/home/gregjules/gdb-6.4.90.dfsg/gdb/event-top.c:797
#8 0xb7f421a0 in rl_callback_read_char () from /lib/libreadline.so.5
#9 0x0811cbdb in rl_callback_read_char_wrapper (client_data=0x0) at
/home/gregjules/gdb-6.4.90.dfsg/gdb/event-top.c:178
#10 0x0811c552 in handle_file_event (event_file_desc=0) at
/home/gregjules/gdb-6.4.90.dfsg/gdb/event-loop.c:730
#11 0x0811b9fd in process_event () at
/home/gregjules/gdb-6.4.90.dfsg/gdb/event-loop.c:343
#12 0x0811c1c5 in gdb_do_one_event (data=0x0) at
/home/gregjules/gdb-6.4.90.dfsg/gdb/event-loop.c:380
#13 0x08118f3b in catch_errors (func=0x811c0b0 <gdb_do_one_event>,
func_args=0x0, errstring=0x8227c00 "", mask=6)
at /home/gregjules/gdb-6.4.90.dfsg/gdb/exceptions.c:515
#14 0x080c19d4 in tui_command_loop (data=0x0) at
/home/gregjules/gdb-6.4.90.dfsg/gdb/tui/tui-interp.c:151
#15 0x0811956f in current_interp_command_loop () at
/home/gregjules/gdb-6.4.90.dfsg/gdb/interps.c:278
#16 0x0807825b in captured_command_loop (data=0x0) at
/home/gregjules/gdb-6.4.90.dfsg/gdb/main.c:101
#17 0x08118f3b in catch_errors (func=0x8078250 <captured_command_loop>,
func_args=0x0, errstring=0x8227c00 "", mask=6)
at /home/gregjules/gdb-6.4.90.dfsg/gdb/exceptions.c:515
#18 0x08078a64 in captured_main (data=0xbf8cf4a4) at
/home/gregjules/gdb-6.4.90.dfsg/gdb/main.c:834
#19 0x08118f3b in catch_errors (func=0x8078290 <captured_main>,
func_args=0xbf8cf4a4, errstring=0x8227c00 "", mask=6)
at /home/gregjules/gdb-6.4.90.dfsg/gdb/exceptions.c:515
#20 0x08078243 in gdb_main (args=0xbf8cf4a4) at
/home/gregjules/gdb-6.4.90.dfsg/gdb/main.c:843
#21 0x08078205 in main (argc=Cannot access memory at address 0x0
) at /home/gregjules/gdb-6.4.90.dfsg/gdb/gdb.c:35
(gdb) p all_pointers
$1 = (struct thread_db_pointers *) 0x0
(gdb) p using_thread_db
$2 = 0
(gdb)
The SEGV occurs in linux-thread-db.c:check_for_thread_db():
void
check_for_thread_db (void)
{
static int already_loaded;
/* First time through, report that libthread_db was successfuly
loaded. Can't print this in in thread_db_load as, at that stage,
the interpreter and it's console haven't started. */
if (!already_loaded)
{
printf_unfiltered (_("Using host libthread_db library \"%s\".\n"),
all_pointers->filename);
already_loaded = 1;
}
...
When <already_loaded> is 0, the above call to printf_unfiltered()
dereferences <all_pointers>, but <all_pointers> can be NULL if, earlier
on, thread_db_load() returned 0 due to verbose_dlsym() returning NULL
for one of the expected thread_db functions.
The segv doesn't occur with gdb-6.4.90 without the debian patches.
The obvious fix makes things work ok:
void
check_for_thread_db (void)
{
static int already_loaded;
/* First time through, report that libthread_db was successfuly
loaded. Can't print this in in thread_db_load as, at that stage,
the interpreter and it's console haven't started. */
if (!already_loaded)
{
if (all_pointers)
printf_unfiltered (_("Using host libthread_db library \"%s\".\n"),
all_pointers->filename);
already_loaded = 1;
}
...
Here are some details of my system:
uname -a:
Linux pc1-debian-etch 2.6.18-3-k7 #1 SMP Mon Dec 4 17:23:11 UTC 2006
i686 GNU/Linux
ls -l /lib/libc.so.6:
lrwxrwxrwx 1 root root 13 2007-01-23 16:48 /lib/libc.so.6 ->
libc-2.3.6.so
I hope that all makes sense.
- Julian
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