On 2009-06-19, Grant Edwards <gra...@visi.com> wrote:
> Is there any documentation on how to set up for remote
> multi-threaded debugging using gdb-server?
[...]
> Here's a typical session:
>
> GNU gdb 6.8
[target remote ....]
[...]
> 0x40000930 in _start () from
> /home/grante/processors/atmel/RM9200/buildroot-2009.05/project_build_arm/uclibc/root/lib/ld-uClibc.so.0
> (gdb) break main
> Breakpoint 1 at 0x8bf4: file hello.c, line 45.
> (gdb) c
> Continuing.
>
> Breakpoint 1, main () at hello.c:45
> 45 pthread_attr_t attr, *attrp=NULL;
> (gdb) next
[...]
> 62 s = pthread_create(tid+i, attrp, thread, (void*)i);
> abort_if_error(s);
> (gdb) next
>
> Program received signal SIG32, Real-time event 32.
> 0x400443d4 in ?? ()
> (gdb)
> Cannot find bounds of current function
Using strace I've verified that
1) The dev-host gdb is finding the target-arch .so files
correctly (I think that can also be deduced from the line
above that says "in _start () from ..../ld-uClibc.so.0")
2) The target gdbserver is finding libthread_db.so.
I've also confirmed that the target arch libpthread .so files
are not stripped (either on the dev-host or on the target).
I've tried using both a stripped and unstripped application
binary on the target. [I always use an unstripped ELF
executable that still has debug symbols on the dev-host as the
target for gdb's "file" command.]
I've got strace output for both gdb and gdbserver, and it
always shows gdbserver responding to a $vCont command with $T4d
immediately before gdb prints the message about SIG32. The
$vCont command in question was the one that was issued as a
result of the "next" command that was stepping through the call
to pthread_create() shown at source file line 62 above:
------------------------------gdb strace------------------------------
send(5, "$vCont;c#a8"..., 11, 0) = 11
select(6, [5], NULL, [5], {1, 0}) = 1 (in [5], left {1, 0})
recv(5, "+"..., 8192, 0) = 1
rt_sigaction(SIGINT, {0x8067350, [INT], SA_RESTART}, {0x80d27f0, [INT],
SA_RESTART}, 8) = 0
select(6, [5], NULL, [5], {1, 0}) = 1 (in [5], left {0, 976000})
recv(5, "$T4d0b:3ccd8dbe;0d:20cb8dbe;0f:d4"..., 8192, 0) = 54
send(5, "+"..., 1, 0) = 1
rt_sigaction(SIGINT, {0x80d27f0, [INT], SA_RESTART}, {0x8067350, [INT],
SA_RESTART}, 8) = 0
write(1, "\n"..., 1) = 1
write(1, "Program received signal SIG32, Re"..., 51) = 51
-----------------------------------------------------------------------
Here's the corrsponding section of the gdbserver strace
------------------------------gdbserver strace--------------------------
read(4, "$vCont;c#a8"..., 4096) = 11
write(4, "+"..., 1) = 1
rt_sigaction(SIGIO, {0xc608, [IO], SA_RESTART|0x4000000}, {0x1, [IO],
SA_RESTART|0x4000000}, 8) = 0
ptrace(PTRACE_PEEKTEXT, 791, 0x8920, [0xe28fc600]) = 0
ptrace(PTRACE_GETREGS, 791, 0, 0x23a08) = 0
ptrace(PTRACE_SETREGS, 791, 0, 0x23a08) = 0
ptrace(PTRACE_CONT, 791, 0, SIG_0) = 0
--- SIGCHLD (Child exited) @ 0 (0) ---
wait4(-1, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGTRAP} | 0x30000], WNOHANG,
NULL) = 791
ptrace(0x4201 /* PTRACE_??? */, 791, 0, 0xbefdcc10) = 0
wait4(792, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGSTOP}], __WALL, NULL) = 792
ptrace(0x4200 /* PTRACE_??? */, 792, 0, 0x8) = 0
ptrace(PTRACE_CONT, 792, 0, SIG_0) = 0
ptrace(PTRACE_CONT, 791, 0, SIG_0) = 0
wait4(-1, 0xbefdcc14, WNOHANG, NULL) = 0
wait4(-1, 0xbefdcc14, WNOHANG|__WCLONE, NULL) = 0
nanosleep({0, 1000000}, 0) = ? ERESTART_RESTARTBLOCK (To be
restarted)
--- SIGCHLD (Child exited) @ 0 (0) ---
restart_syscall(<... resuming interrupted call ...>) = 0
wait4(-1, 0xbefdcc14, WNOHANG, NULL) = 0
wait4(-1, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGSTOP}], WNOHANG|__WCLONE,
NULL) = 793
wait4(-1, 0xbefdcc14, WNOHANG, NULL) = 0
wait4(-1, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGTRAP} | 0x30000],
WNOHANG|__WCLONE, NULL) = 792
ptrace(0x4201 /* PTRACE_??? */, 792, 0, 0xbefdcc10) = 0
ptrace(0x4200 /* PTRACE_??? */, 793, 0, 0x8) = 0
ptrace(PTRACE_CONT, 793, 0, SIG_0) = 0
ptrace(PTRACE_CONT, 792, 0, SIG_0) = 0
--- SIGCHLD (Child exited) @ 0 (0) ---
wait4(-1, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGRTMIN}], WNOHANG, NULL) = 791
syscall(0x9000ee, 0x318, 0x13, 0, 0x23b48) = 0
--- SIGCHLD (Child exited) @ 0 (0) ---
syscall(0x9000ee, 0x319, 0x13, 0, 0) = 0
--- SIGCHLD (Child exited) @ 0 (0) ---
wait4(792, 0xbefdcbf4, WNOHANG, NULL) = -1 ECHILD (No child processes)
wait4(792, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGSTOP}], WNOHANG|__WCLONE,
NULL) = 792
wait4(793, 0xbefdcbf4, WNOHANG, NULL) = -1 ECHILD (No child processes)
wait4(793, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGSTOP}], WNOHANG|__WCLONE,
NULL) = 793
ptrace(PTRACE_GETREGS, 791, 0, 0x23c68) = 0
rt_sigaction(SIGIO, {0x1, [IO], SA_RESTART|0x4000000}, {0xc608, [IO],
SA_RESTART|0x4000000}, 8) = 0
write(4, "$T4d0b:4cfdc6be;0d:30fbc6be;0f:d4"..., 54) = 54
--- SIGIO (I/O possible) @ 0 (0) ---
------------------------------------------------------------------------
I'm trying to figure out which end is broken (gdb or
gdbserver), but I can't find any documetnation on what is
supposed to happen when a new thread is created. My guess is
that gdbserver isn't working right, but that's just a hunch.
--
Grant Edwards grante Yow! Hold the MAYO & pass
at the COSMIC AWARENESS ...
visi.com
