Hi,
i'm a system administrator, not a developer. I use strace sometimes for
debugging problems, and i like it very much. Nice tool.
I have some principal questions and hope this is the right place to ask. If not
please inform me and maybe give me a hint
where a more aprropriate place would be.
From what i understand until now is that processes normally don't invoke system
calls directly, they contact libraries which do it for them.
Starting a process give me this error in the log:
traps: nsrexecd[12162] general protection ip:7f085e4cb960 sp:7f085a4e9278
error:0 in libpthread-2.23.so[7f085e4b9000+18000]
It seems that the kernel is stopping the process because of ... what with a
signal.
I observed the process /usr/sbin/nsrexecd with strace.
Here seems to be the problem:
open("/dev/null", O_RDWR) = 3
close(3) = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x7fac73d019d0) = 13025
rt_sigaction(SIGTERM, {0x4275e0, [HUP INT USR1 USR2 PIPE ALRM TERM CHLD XCPU
XFSZ], SA_RESTORER, 0x7fac72ce83d0}, NULL, 8) = 0
rt_sigaction(SIGCHLD, {0x4275e0, [HUP INT USR1 USR2 PIPE ALRM TERM CHLD XCPU
XFSZ], SA_RESTORER, 0x7fac72ce83d0}, NULL, 8) = 0
select(0, NULL, NULL, NULL, {300, 0}) = ? ERESTARTNOHAND (To be restarted if
no handler)
--- SIGTERM {si_signo=SIGTERM, si_code=SI_USER, si_pid=13025, si_uid=0} ---
rt_sigreturn({mask=[]}) = -1 EINTR (Interrupted system call)
exit_group(0) = ?
+++ exited with 0 +++
clone is a syscall for creating a child process, right ?
man 2 clone says:
/* Prototype for the glibc wrapper function */
#include <sched.h>
int clone(int (*fn)(void *), void *child_stack,
int flags, void *arg, ...
/* pid_t *ptid, struct user_desc *tls, pid_t *ctid */ );
/* Prototype for the raw system call */
long clone(unsigned long flags, void *child_stack,
void *ptid, void *ctid,
struct pt_regs *regs);
What i don't understand:
The syscall is called with three arguments, right ? But the wrapper function
expects ... how many arguments ? What means ... ? Does it expect 7 arguments ?
And the syscall itself has 5 arguments, but it is called just with three. Does
that work ? Which ones are the these which are used ? The first three ?
The last three ?
What means the return code 13025 ? I didn't find anything about it in the net.
Is there s.th. where i can get further information ?
I installed the kernel sources and searched for a file like clone.h or clone.c,
but didn't find anything.
Thanks for any help.
Bernd
--
Bernd Lentes
Systemadministration
institute of developmental genetics
Gebäude 35.34 - Raum 208
HelmholtzZentrum München
bernd.len...@helmholtz-muenchen.de
phone: +49 (0)89 3187 1241
fax: +49 (0)89 3187 2294
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