truss

[Anton Yuzhaninov]

On Mon, 19 Sep 2011 15:00:31 +0000 (UTC), Anton Yuzhaninov wrote:
AY> On Mon, 19 Sep 2011 15:58:02 +0300, Mikolaj Golub wrote:
 AY>>> ktrace -i for truss sleep 5
 AY>>> http://dl.dropbox.com/u/8798217/tmp/truss_ktrace2.txt
MG>> 
MG>> Although ptrace(PT_TRACE_ME,0,0,0) returned 0 the process did not stop after
MG>> execve() and wait4() in parent (which was actually waiting for this stop)
MG>> returned only after the child exit. No I idea why so far :-).
MG>> 
AY> 
AY> As I understand SIGTRAP used to stop child process after execve(), but
AY> this signal ignored:
AY> 
AY> citrin:~> sleep 300 &
AY> citrin:~> procstat -i 1991 | fgrep TRAP
AY>  1991 sleep            TRAP     -I-
AY> 
AY> Under FreeBSD 8, where ptrace works for me, this signal is not ignored:
AY> x:~> sleep 300 &
AY> x:~> procstat -i 78716 | fgrep TRAP
AY> 78716 sleep            TRAP     ---

SIGTRAP is ignored by X window manager used by me, and this is inherited across
forks/execs up to the truss.

IMHO truss should restore default signal handler for SIGTRAP.

With this patch truss works for me:

--- usr.bin/truss/main.c        (revision 225504)
+++ usr.bin/truss/main.c        (working copy)
@@ -255,6 +255,11 @@ main(int ac, char **av)

        if (trussinfo->pid == 0) {      /* Start a command ourselves */
                command = av;
+               /*
+                * SIGTRUP used to stop traced process after execve
+                * un-ignore this signal (it can be ignored by parents)
+                */
+               signal(SIGTRAP, SIG_DFL);
                trussinfo->pid = setup_and_wait(command);
                signal(SIGINT, SIG_IGN);
                signal(SIGTERM, SIG_IGN);

-- 
 Anton Yuzhaninov