Experimental support for -D option.
Unlike normal case, with -D *grandparent* process exec's, becoming a traced process. Child exits (this prevents traced process from having children it doesn't expect to have), and grandchild attaches to grandparent similarly to strace -p PID. This allows for more transparent interaction in cases when process and its parent are communicating via signals, wait() etc. Without -D, strace process gets lodged in between, disrupting parent<->child link. * strace.c: Add global flag variable daemonized_tracer for -D option. (startup_attach): If -D, fork and block parent in pause(). In this case we are already a child, we in fact created a grandchild. After attaching to grandparent, grandchild SIGKILLs parent. (startup_child): If -D, parent blocks in wait(), then execs the program to strace. Normally (w/o -D), it is child who execs the program. (main): Detect -D option, call startup_attach() if it is given.
This commit is contained in:
Denys Vlasenko
20
ChangeLog
20
ChangeLog
@ -1,3 +1,23 @@
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2008-12-30 Denys Vlasenko <dvlasenk@redhat.com>
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Experimental support for -D option.
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Unlike normal case, with -D *grandparent* process exec's,
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becoming a traced process. Child exits (this prevents traced process
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from having children it doesn't expect to have), and grandchild
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attaches to grandparent similarly to strace -p PID.
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This allows for more transparent interaction in cases
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when process and its parent are communicating via signals,
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wait() etc. Without -D, strace process gets lodged in between,
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disrupting parent<->child link.
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* strace.c: Add global flag variable daemonized_tracer for -D option.
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(startup_attach): If -D, fork and block parent in pause().
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In this case we are already a child, we in fact created a grandchild.
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After attaching to grandparent, grandchild SIGKILLs parent.
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(startup_child): If -D, parent blocks in wait(), then
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execs the program to strace. Normally (w/o -D), it is child
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who execs the program.
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(main): Detect -D option, call startup_attach() if it is given.
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2008-12-30 Kirill A. Shutemov <kirill@shutemov.name>
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Fix some warnings on ARM build.
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146
strace.c
146
strace.c
@ -83,6 +83,19 @@ extern char **environ;
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int debug = 0, followfork = 0;
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int dtime = 0, cflag = 0, xflag = 0, qflag = 0;
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static int iflag = 0, interactive = 0, pflag_seen = 0, rflag = 0, tflag = 0;
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/*
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* daemonized_tracer supports -D option.
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* With this option, strace forks twice.
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* Unlike normal case, with -D *grandparent* process exec's,
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* becoming a traced process. Child exits (this prevents traced process
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* from having children it doesn't expect to have), and grandchild
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* attaches to grandparent similarly to strace -p PID.
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* This allows for more transparent interaction in cases
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* when process and its parent are communicating via signals,
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* wait() etc. Without -D, strace process gets lodged in between,
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* disrupting parent<->child link.
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*/
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static bool daemonized_tracer = 0;
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/* Sometimes we want to print only succeeding syscalls. */
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int not_failing_only = 0;
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@ -159,7 +172,7 @@ int exitval;
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usage: strace [-dffhiqrtttTvVxx] [-a column] [-e expr] ... [-o file]\n\
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[-p pid] ... [-s strsize] [-u username] [-E var=val] ...\n\
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[command [arg ...]]\n\
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or: strace -c [-e expr] ... [-O overhead] [-S sortby] [-E var=val] ...\n\
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or: strace -c -D [-e expr] ... [-O overhead] [-S sortby] [-E var=val] ...\n\
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[command [arg ...]]\n\
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-c -- count time, calls, and errors for each syscall and report summary\n\
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-f -- follow forks, -ff -- with output into separate files\n\
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@ -176,6 +189,7 @@ usage: strace [-dffhiqrtttTvVxx] [-a column] [-e expr] ... [-o file]\n\
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-o file -- send trace output to FILE instead of stderr\n\
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-O overhead -- set overhead for tracing syscalls to OVERHEAD usecs\n\
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-p pid -- trace process with process id PID, may be repeated\n\
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-D -- run tracer process as a detached grandchild, not as parent\n\
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-s strsize -- limit length of print strings to STRSIZE chars (default %d)\n\
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-S sortby -- sort syscall counts by: time, calls, name, nothing (default %s)\n\
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-u username -- run command as username handling setuid and/or setgid\n\
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@ -362,6 +376,23 @@ startup_attach(void)
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if (interactive)
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sigprocmask(SIG_BLOCK, &blocked_set, NULL);
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if (daemonized_tracer) {
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pid_t pid = fork();
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if (pid < 0) {
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_exit(1);
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}
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if (pid) { /* parent */
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/*
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* Wait for child to attach to straced process
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* (our parent). Child SIGKILLs us after it attached.
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* Parent's wait() is unblocked by our death,
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* it proceeds to exec the straced program.
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*/
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pause();
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_exit(0); /* paranoia */
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}
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}
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for (tcbi = 0; tcbi < tcbtabsize; tcbi++) {
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tcp = tcbtab[tcbi];
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if (!(tcp->flags & TCB_INUSE) || !(tcp->flags & TCB_ATTACHED))
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@ -383,7 +414,7 @@ startup_attach(void)
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}
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#else /* !USE_PROCFS */
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# ifdef LINUX
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if (followfork) {
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if (followfork && !daemonized_tracer) {
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char procdir[MAXPATHLEN];
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DIR *dir;
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@ -452,6 +483,20 @@ Process %u attached - interrupt to quit\n",
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continue;
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}
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/* INTERRUPTED is going to be checked at the top of TRACE. */
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if (daemonized_tracer) {
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/*
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* It is our grandparent we trace, not a -p PID.
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* Don't want to just detach on exit, so...
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*/
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tcp->flags &= ~TCB_ATTACHED;
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/*
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* Make parent go away.
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* Also makes grandparent's wait() unblock.
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*/
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kill(getppid(), SIGKILL);
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}
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#endif /* !USE_PROCFS */
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if (!qflag)
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fprintf(stderr,
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@ -530,13 +575,15 @@ startup_child (char **argv)
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exit(1);
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}
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strace_child = pid = fork();
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switch (pid) {
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case -1:
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if (pid < 0) {
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perror("strace: fork");
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cleanup();
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exit(1);
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break;
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case 0: {
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}
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if ((pid != 0 && daemonized_tracer) /* parent: to become a traced process */
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|| (pid == 0 && !daemonized_tracer) /* child: to become a traced process */
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) {
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pid = getpid();
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#ifdef USE_PROCFS
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if (outf != stderr) close (fileno (outf));
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#ifdef MIPS
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@ -549,18 +596,20 @@ startup_child (char **argv)
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#ifndef FREEBSD
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pause();
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#else /* FREEBSD */
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kill(getpid(), SIGSTOP); /* stop HERE */
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kill(pid, SIGSTOP); /* stop HERE */
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#endif /* FREEBSD */
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#else /* !USE_PROCFS */
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if (outf!=stderr)
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close(fileno (outf));
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if (ptrace(PTRACE_TRACEME, 0, (char *) 1, 0) < 0) {
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perror("strace: ptrace(PTRACE_TRACEME, ...)");
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exit(1);
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if (!daemonized_tracer) {
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if (ptrace(PTRACE_TRACEME, 0, (char *) 1, 0) < 0) {
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perror("strace: ptrace(PTRACE_TRACEME, ...)");
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exit(1);
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}
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if (debug)
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kill(pid, SIGSTOP);
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}
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if (debug)
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kill(getpid(), SIGSTOP);
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if (username != NULL || geteuid() == 0) {
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uid_t run_euid = run_uid;
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@ -593,33 +642,54 @@ startup_child (char **argv)
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else
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setreuid(run_uid, run_uid);
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/*
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* Induce an immediate stop so that the parent
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* will resume us with PTRACE_SYSCALL and display
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* this execve call normally.
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*/
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kill(getpid(), SIGSTOP);
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if (!daemonized_tracer) {
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/*
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* Induce an immediate stop so that the parent
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* will resume us with PTRACE_SYSCALL and display
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* this execve call normally.
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*/
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kill(getpid(), SIGSTOP);
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} else {
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struct sigaction sv_sigchld;
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sigaction(SIGCHLD, NULL, &sv_sigchld);
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/*
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* Make sure it is not SIG_IGN, otherwise wait
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* will not block.
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*/
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signal(SIGCHLD, SIG_DFL);
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/*
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* Wait for grandchild to attach to us.
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* It kills child after that, and wait() unblocks.
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*/
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alarm(3);
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wait(NULL);
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alarm(0);
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sigaction(SIGCHLD, &sv_sigchld, NULL);
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}
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#endif /* !USE_PROCFS */
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execv(pathname, argv);
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perror("strace: exec");
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_exit(1);
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break;
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}
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default:
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if ((tcp = alloctcb(pid)) == NULL) {
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cleanup();
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exit(1);
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}
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/* We are the tracer. */
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tcp = alloctcb(daemonized_tracer ? getppid() : pid);
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if (tcp == NULL) {
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cleanup();
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exit(1);
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}
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if (daemonized_tracer) {
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/* We want subsequent startup_attach() to attach to it. */
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tcp->flags |= TCB_ATTACHED;
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}
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#ifdef USE_PROCFS
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if (proc_open(tcp, 0) < 0) {
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fprintf(stderr, "trouble opening proc file\n");
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cleanup();
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exit(1);
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}
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#endif /* USE_PROCFS */
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break;
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if (proc_open(tcp, 0) < 0) {
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fprintf(stderr, "trouble opening proc file\n");
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cleanup();
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exit(1);
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}
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#endif /* USE_PROCFS */
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}
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int
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@ -658,7 +728,11 @@ main(int argc, char *argv[])
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qualify("verbose=all");
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qualify("signal=all");
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while ((c = getopt(argc, argv,
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"+cdfFhiqrtTvVxza:e:o:O:p:s:S:u:E:")) != EOF) {
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"+cdfFhiqrtTvVxz"
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#ifndef USE_PROCFS
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"D"
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#endif
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"a:e:o:O:p:s:S:u:E:")) != EOF) {
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switch (c) {
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case 'c':
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cflag++;
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@ -667,6 +741,12 @@ main(int argc, char *argv[])
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case 'd':
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debug++;
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break;
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#ifndef USE_PROCFS
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/* Experimental, not documented in manpage yet. */
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case 'D':
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daemonized_tracer = 1;
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break;
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#endif
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case 'F':
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optF = 1;
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break;
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@ -880,7 +960,7 @@ main(int argc, char *argv[])
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sigaction(SIGCHLD, &sa, NULL);
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#endif /* USE_PROCFS */
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if (pflag_seen)
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if (pflag_seen || daemonized_tracer)
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startup_attach();
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if (trace() < 0)
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