This is the mail archive of the
archer@sourceware.org
mailing list for the Archer project.
[BUG] gdb: quit hangs after step into signal handler
- From: Oleg Nesterov <oleg at redhat dot com>
- To: archer at sourceware dot org
- Date: Mon, 20 Sep 2010 23:17:15 +0200
- Subject: [BUG] gdb: quit hangs after step into signal handler
In short, gdb uses ptrace(PTRACE_KILL) + wait() to detach/kill the tracee.
Well, I think PTRACE_KILL should be avoided but this is offtopic,
ptrace(PTRACE_CONT, SIGKILL) has the same problem if the tracee has
stepped into the signal handler.
$ gdb /usr/bin/perl
GNU gdb (GDB) 7.1
...
(gdb)
(gdb) set args -e '$SIG{HUP}=sub{}; kill HUP, $$; 1 while 1'
(this sets a signal handler for SIGHUP, sends SIGHUP to itself, then
spins forever)
(gdb) r
Starting program: /usr/bin/perl -e '$SIG{HUP}=sub{}; kill HUP, $$; 1 while 1'
[Thread debugging using libthread_db enabled]
Program received signal SIGHUP, Hangup.
0x000000375fa32507 in kill () from /lib64/libc.so.6
(gdb) si
0x00000037522a2a40 in Perl_csighandler () from /usr/lib64/perl5/5.10.0/x86_64-linux-thread-multi/CORE/libperl.so
(step into handler)
(gdb) q
A debugging session is active.
Inferior 1 [process 9694] will be killed.
Quit anyway? (y or n) y
(ptrace(PTRACE_KILL) + wait)
Hangs "forever" in wait4().
At first I thought this is another bug in ptrace-utrace (and I even
started doing the patch), but then I recalled that this is what
upstream does, and ptrace-utrace just tries to be compatible.
There is no signal context after step-into-handler, ptrace(PTRACE_KILL)
or ptrace(PTRACE_CONT, SIGKILL) acts like ptrace(CONT, pid, 0,0) and
just resumes the tracee.
Probably gdb should just do kill(tracee, SIGKILL) when it wants
to terminate the tracee.
Oleg.