kgdb crashing on a vmcore with dumptid = 0

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Eitan Adler

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May 5, 2018, 1:53:59 AM5/5/18
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gdb$ bt
#0 thr_kill () at thr_kill.S:3
#1 0x00000008035046b4 in __raise (s=0x6) at /usr/src/lib/libc/gen/raise.c:54
#2 0x0000000803504629 in abort () at /usr/src/lib/libc/stdlib/abort.c:67
#3 0x0000000000c805c6 in dump_core () at utils.c:284
#4 0x0000000000c81920 in internal_vproblem (problem=0x24bd890
<internal_error_problem>, file=0x15c560e "inferior.c", line=0x135,
fmt=0x15780ac "%s: Assertion
`%s' failed.", ap=0x7fffffffb9e0) at utils.c:493
#5 0x0000000000c806d8 in internal_verror (file=0x15c560e
"inferior.c", line=0x135, fmt=0x15780ac "%s: Assertion `%s' failed.",
ap=0x7fffffffb9e0) at utils.c:
518
#6 0x00000000008363a8 in internal_error (file=0x15c560e "inferior.c",
line=0x135, fmt=0x15780ac "%s: Assertion `%s' failed.") at
common/errors.c:55
#7 0x0000000000a8397e in find_inferior_pid (pid=0x0) at inferior.c:309
#8 0x0000000000a83d54 in find_inferior_ptid (ptid=...) at inferior.c:323
#9 0x0000000000c10049 in default_thread_architecture (ops=0x2702d90
<dummy_target>, ptid=...) at target.c:3131
#10 0x0000000000bfec2b in delegate_thread_architecture (self=0x2702d90
<dummy_target>, arg1=...) at ./target-delegates.c:2525
#11 0x0000000000bfec2b in delegate_thread_architecture (self=0x26eedd0
<exec_ops>, arg1=...) at ./target-delegates.c:2525
#12 0x0000000000bfec2b in delegate_thread_architecture (self=0x26ec280
<kgdb_trgt_ops>, arg1=...) at ./target-delegates.c:2525
#13 0x0000000000b53cba in get_thread_regcache (ptid=...) at regcache.c:439
#14 0x0000000000b53d5e in get_current_regcache () at regcache.c:448
#15 0x0000000000713077 in kgdb_trgt_open (arg=0x80410900e "vmcore.2",
from_tty=0x1) at fbsd-kvm.c:335
#16 0x0000000000bf3980 in open_target (args=0x80410900e "vmcore.2",
from_tty=0x1, command=0x8041c8f40) at target.c:356
#17 0x0000000000722c35 in do_sfunc (c=0x8041c8f40, args=0x80410900e
"vmcore.2", from_tty=0x1) at cli/cli-decode.c:122
#18 0x0000000000726b5a in cmd_func (cmd=0x8041c8f40, args=0x80410900e
"vmcore.2", from_tty=0x1) at cli/cli-decode.c:1886
#19 0x0000000000c450c7 in execute_command (p=0x804109015 "2",
from_tty=0x1) at top.c:630
#20 0x0000000000acd4a8 in catch_command_errors (command=0xc445f0
<execute_command(char const*, int)>, arg=0x804109000 "target vmcore
vmcore.2", from_tty=0x1)
at main.c:378
#21 0x0000000000accdf2 in captured_main_1 (context=0x7fffffffcfe8) at
main.c:1124
#22 0x0000000000aca62d in captured_main (data=0x7fffffffcfe8) at main.c:1146
#23 0x0000000000aca508 in gdb_main (args=0x7fffffffcfe8) at main.c:1172
#24 0x000000000050bd5b in main (argc=0x3, argv=0x7fffffffd558) at
kgdb-main.c:410

gdb$ up 7
#7 0x0000000000a8397e in find_inferior_pid (pid=0x0) at inferior.c:309
309 gdb_assert (pid != 0);
gdb$ frame
Stack level 7, frame at 0x7fffffffba50:
rip = 0xa8397e in find_inferior_pid (inferior.c:309); saved rip = 0xa83d54
called by frame at 0x7fffffffba60, caller of frame at 0x7fffffffba20
source language c++.
Arglist at 0x7fffffffba40, args: pid=0x0
Locals at 0x7fffffffba40, Previous frame's sp is 0x7fffffffba50
Saved registers:
rbp at 0x7fffffffba40, rip at 0x7fffffffba48
pid = 0x0
inf = 0x8415d5 <ptid_get_pid(ptid_t const&)+21>


gdb$ list
304 struct inferior *inf;
305
306 /* Looking for inferior pid == 0 is always wrong, and indicative of
307 a bug somewhere else. There may be more than one with pid == 0,
308 for instance. */
309 gdb_assert (pid != 0);
310
311 for (inf = inferior_list; inf; inf = inf->next)
312 if (inf->pid == pid)
313 return inf;


gdb$ p pid
$1 = 0x0


gdb$ p ptid
$2 = {
m_pid = 0x0,
m_lwp = 0x0,
m_tid = 0x0
}

gdb$ up
#9 0x0000000000c10049 in default_thread_architecture (ops=0x2702d90
<dummy_target>, ptid=...) at target.c:3131
3131 inferior *inf = find_inferior_ptid (ptid);
gdb$ list
3126 }
3127
3128 static struct gdbarch *
3129 default_thread_architecture (struct target_ops *ops, ptid_t ptid)
3130 {
3131 inferior *inf = find_inferior_ptid (ptid);
3132 gdb_assert (inf != NULL);
3133 return inf->gdbarch;
3134 }
3135
gdb$ p ops
$4 = (target_ops *) 0x2702d90 <dummy_target>

gdb$ up
#14 0x0000000000b53d5e in get_current_regcache () at regcache.c:448
448 return get_thread_regcache (inferior_ptid);
gdb$ list
443 }
444
445 struct regcache *
446 get_current_regcache (void)
447 {
448 return get_thread_regcache (inferior_ptid);
449 }
450
451 /* See common/common-regcache.h. */
452
gdb$ p inferior_ptid
$13 = {
m_pid = 0x0,
m_lwp = 0x0,
m_tid = 0x0
}


gdb$ up
#15 0x0000000000713077 in kgdb_trgt_open (arg=0x80410900e "vmcore.2",
from_tty=0x1) at fbsd-kvm.c:335
335 target_fetch_registers (get_current_regcache (), -1);
gdb$ list
330 kt = kgdb_thr_next(kt);
331 }
332 if (curkthr != 0)
333 inferior_ptid = fbsd_vmcore_ptid(curkthr->tid);
334
335 target_fetch_registers (get_current_regcache (), -1);
336
337 reinit_frame_cache ();
338 print_stack_frame (get_selected_frame (NULL), 0,
SRC_AND_LOC, 1);
339 }
gdb$ p inferior_ptid
$17 = {
m_pid = 0x0,
m_lwp = 0x0,
m_tid = 0x0
}
gdb$ p curkthr
$18 = (kthr *) 0x0

gdb$ frame
Stack level 15, frame at 0x7fffffffbd90:
rip = 0x713077 in kgdb_trgt_open (fbsd-kvm.c:335); saved rip = 0xbf3980
called by frame at 0x7fffffffbdc0, caller of frame at 0x7fffffffbc40
source language c++.
Arglist at 0x7fffffffbd80, args: arg=0x80410900e "vmcore.2", from_tty=0x1
Locals at 0x7fffffffbd80, Previous frame's sp is 0x7fffffffbd90
Saved registers:
rbp at 0x7fffffffbd80, rip at 0x7fffffffbd88
arg = 0x80410900e "vmcore.2"
from_tty = 0x1
ops = 0x8043ef840
inf = 0x80442de80
old_chain = 0x804431820
ti = 0x7fffffffd550
kt = 0x0
nkvm = 0x804363800
temp = 0x8047f33b0 "/home/eax/crashes/aes_gpault_crash/vmcore.2"
kernel = 0x8043dec80 "/home/eax/crashes/aes_gpault_crash/kernel/kernel"
filename = 0x8047f33b0 "/home/eax/crashes/aes_gpault_crash/vmcore.2"
ontop = 0x0

gdb$ p curkthr
$19 = (kthr *) 0x0

which is coming from

curkthr = kgdb_thr_lookup_tid(dumptid);
if (curkthr == NULL)
curkthr = first;

gdb$ p dumptid
$20 = 0x0

which is coming from

TRY {
dumptid = parse_and_eval_long("dumptid");
} CATCH(e, RETURN_MASK_ERROR) {
dumptid = -1;
} END_CATCH

which is getting into a bit deeper gdb internals than I want to deal
with right now.

If anyone feels like like looking into this, a full set of debugging
information is available including my kernel, the vmcore, the gdb
image, the gdb core, etc.

I'll also try and spend some more time on this over the next few weeks.

--
Eitan Adler
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John Baldwin

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Jun 15, 2018, 6:13:59 PM6/15/18
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Notice this fall back though. If dumptid isn't valid this falls back to
just picking the first thread. Instead, it seems that in your dump kgdb
didn't find any kthreads at all. Is 'kernel' a stripped kernel without
any debug symbols? You should try single-stepping kgdb_thr_init to see
if it finds valid offsets of structure members in 'struct thread' and
'struct proc'.

--
John Baldwin
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