This change decouples waiting for next event from reacting to it. This makes the control flow easier to understand, and serves as a preparation for implementing a pull-style API for LuaJIT.
* strace.c (enum trace_event): New enum. (trace): Split into... (next_event, dispatch_event): ...new functions. (main): Use them. --- strace.c | 351 ++++++++++++++++++++++++++++++++++++++------------------------- 1 file changed, 211 insertions(+), 140 deletions(-) diff --git a/strace.c b/strace.c index 42650ab..0d3c8e9 100644 --- a/strace.c +++ b/strace.c @@ -2252,21 +2252,76 @@ print_event_exit(struct tcb *tcp) line_ended(); } -/* Returns true iff the main trace loop has to continue. */ -static bool -trace(void) +enum trace_event { + /* Break the main loop. */ + TE_BREAK, + + /* Call next_event() again. */ + TE_NEXT, + + /* Restart the tracee with signal 0 and call next_event() again. */ + TE_RESTART, + + /* + * For all the events below, current_tcp is set to current tracee's tcb. + * All the suggested actions imply that you want to continue the tracing of the current + * tracee; alternatively, you can detach it. + */ + + /* + * Syscall entry or exit. + * Restart the tracee with signal 0, or with an injected signal number. + */ + TE_SYSCALL_STOP, + + /* + * Tracee received signal with number WSTOPSIG(*pstatus); signal info is written to *si. + * Restart the tracee (with that signal number if you want to deliver it). + */ + TE_SIGNAL_DELIVERY_STOP, + + /* + * Tracee was killed by a signal with number WTERMSIG(*pstatus). + */ + TE_SIGNALLED, + + /* + * Tracee was stopped by a signal with number WSTOPSIG(*pstatus). + * Restart the tracee with that signal number. + */ + TE_GROUP_STOP, + + /* + * Tracee exited with status WEXITSTATUS(*pstatus). + */ + TE_EXITED, + + /* + * Tracee is going to perform execve(). + * Restart the tracee with signal 0. + */ + TE_STOP_BEFORE_EXECVE, + + /* + * Tracee is going to terminate. + * Restart the tracee with signal 0. + */ + TE_STOP_BEFORE_EXIT, +}; + +static enum trace_event +next_event(int *pstatus, siginfo_t *si) { int pid; int wait_errno; int status; - bool stopped; unsigned int sig; unsigned int event; struct tcb *tcp; struct rusage ru; if (interrupted) - return false; + return TE_BREAK; /* * Used to exit simply when nprocs hits zero, but in this testcase: @@ -2286,21 +2341,21 @@ trace(void) * on exit. Oh well... */ if (nprocs == 0) - return false; + return TE_BREAK; } if (interactive) sigprocmask(SIG_SETMASK, &start_set, NULL); - pid = wait4(-1, &status, __WALL, (cflag ? &ru : NULL)); + pid = wait4(-1, pstatus, __WALL, (cflag ? &ru : NULL)); wait_errno = errno; if (interactive) sigprocmask(SIG_SETMASK, &blocked_set, NULL); if (pid < 0) { if (wait_errno == EINTR) - return true; + return TE_NEXT; if (nprocs == 0 && wait_errno == ECHILD) - return false; + return TE_BREAK; /* * If nprocs > 0, ECHILD is not expected, * treat it as any other error here: @@ -2309,10 +2364,12 @@ trace(void) perror_msg_and_die("wait4(__WALL)"); } + status = *pstatus; + if (pid == popen_pid) { if (!WIFSTOPPED(status)) popen_pid = 0; - return true; + return TE_NEXT; } if (debug_flag) @@ -2324,61 +2381,29 @@ trace(void) if (!tcp) { tcp = maybe_allocate_tcb(pid, status); if (!tcp) - return true; + return TE_NEXT; } clear_regs(); event = (unsigned int) status >> 16; - if (event == PTRACE_EVENT_EXEC) { - /* - * Under Linux, execve changes pid to thread leader's pid, - * and we see this changed pid on EVENT_EXEC and later, - * execve sysexit. Leader "disappears" without exit - * notification. Let user know that, drop leader's tcb, - * and fix up pid in execve thread's tcb. - * Effectively, execve thread's tcb replaces leader's tcb. - * - * BTW, leader is 'stuck undead' (doesn't report WIFEXITED - * on exit syscall) in multithreaded programs exactly - * in order to handle this case. - * - * PTRACE_GETEVENTMSG returns old pid starting from Linux 3.0. - * On 2.6 and earlier, it can return garbage. - */ - if (os_release >= KERNEL_VERSION(3,0,0)) - tcp = maybe_switch_tcbs(tcp, pid); - - if (detach_on_execve) { - if (tcp->flags & TCB_SKIP_DETACH_ON_FIRST_EXEC) { - tcp->flags &= ~TCB_SKIP_DETACH_ON_FIRST_EXEC; - } else { - detach(tcp); /* do "-b execve" thingy */ - return true; - } - } - } - /* Set current output file */ current_tcp = tcp; + if (event == PTRACE_EVENT_EXEC) + return TE_STOP_BEFORE_EXECVE; + if (cflag) { tv_sub(&tcp->dtime, &ru.ru_stime, &tcp->stime); tcp->stime = ru.ru_stime; } - if (WIFSIGNALED(status)) { - print_signalled(tcp, pid, status); - droptcb(tcp); - return true; - } + if (WIFSIGNALED(status)) + return TE_SIGNALLED; - if (WIFEXITED(status)) { - print_exited(tcp, pid, status); - droptcb(tcp); - return true; - } + if (WIFEXITED(status)) + return TE_EXITED; if (!WIFSTOPPED(status)) { /* @@ -2387,128 +2412,172 @@ trace(void) */ error_msg("pid %u not stopped!", pid); droptcb(tcp); - return true; + return TE_NEXT; } /* Is this the very first time we see this tracee stopped? */ - if (tcp->flags & TCB_STARTUP) { + if (tcp->flags & TCB_STARTUP) startup_tcb(tcp); - } sig = WSTOPSIG(status); switch (event) { - case 0: - break; - case PTRACE_EVENT_EXIT: - print_event_exit(tcp); - goto restart_tracee_with_sig_0; -#if USE_SEIZE - case PTRACE_EVENT_STOP: + case 0: + /* + * Is this post-attach SIGSTOP? + * Interestingly, the process may stop + * with STOPSIG equal to some other signal + * than SIGSTOP if we happend to attach + * just before the process takes a signal. + */ + if (sig == SIGSTOP && (tcp->flags & TCB_IGNORE_ONE_SIGSTOP)) { + if (debug_flag) + error_msg("ignored SIGSTOP on pid %d", tcp->pid); + tcp->flags &= ~TCB_IGNORE_ONE_SIGSTOP; + return TE_RESTART; + } else if (sig == syscall_trap_sig) { + return TE_SYSCALL_STOP; + } else { + *si = (siginfo_t) {}; /* - * PTRACE_INTERRUPT-stop or group-stop. - * PTRACE_INTERRUPT-stop has sig == SIGTRAP here. + * True if tracee is stopped by signal + * (as opposed to "tracee received signal"). + * TODO: shouldn't we check for errno == EINVAL too? + * We can get ESRCH instead, you know... */ - switch (sig) { - case SIGSTOP: - case SIGTSTP: - case SIGTTIN: - case SIGTTOU: - stopped = true; - goto show_stopsig; - } - /* fall through */ + bool stopped = ptrace(PTRACE_GETSIGINFO, pid, 0, si) < 0; + return stopped ? TE_GROUP_STOP : TE_SIGNAL_DELIVERY_STOP; + } + break; +#if USE_SEIZE + case PTRACE_EVENT_STOP: + /* + * PTRACE_INTERRUPT-stop or group-stop. + * PTRACE_INTERRUPT-stop has sig == SIGTRAP here. + */ + switch (sig) { + case SIGSTOP: + case SIGTSTP: + case SIGTTIN: + case SIGTTOU: + return TE_GROUP_STOP; + } + return TE_RESTART; #endif - default: - goto restart_tracee_with_sig_0; + case PTRACE_EVENT_EXIT: + return TE_STOP_BEFORE_EXIT; + default: + return TE_RESTART; } +} - /* - * Is this post-attach SIGSTOP? - * Interestingly, the process may stop - * with STOPSIG equal to some other signal - * than SIGSTOP if we happend to attach - * just before the process takes a signal. - */ - if (sig == SIGSTOP && (tcp->flags & TCB_IGNORE_ONE_SIGSTOP)) { - if (debug_flag) - error_msg("ignored SIGSTOP on pid %d", tcp->pid); - tcp->flags &= ~TCB_IGNORE_ONE_SIGSTOP; - goto restart_tracee_with_sig_0; - } +/* Returns true iff the main trace loop has to continue. */ +static bool +dispatch_event(enum trace_event ret, int *pstatus, siginfo_t *si) +{ + unsigned int restart_op = PTRACE_SYSCALL; + unsigned int restart_sig = 0; - if (sig != syscall_trap_sig) { - siginfo_t si = {}; + switch (ret) { + case TE_BREAK: + return false; - /* - * True if tracee is stopped by signal - * (as opposed to "tracee received signal"). - * TODO: shouldn't we check for errno == EINVAL too? - * We can get ESRCH instead, you know... - */ - stopped = ptrace(PTRACE_GETSIGINFO, pid, 0, &si) < 0; -#if USE_SEIZE -show_stopsig: -#endif - print_stopped(tcp, stopped ? NULL : &si, sig); + case TE_NEXT: + return true; - if (!stopped) - /* It's signal-delivery-stop. Inject the signal */ - goto restart_tracee; + case TE_RESTART: + break; - /* It's group-stop */ + case TE_SYSCALL_STOP: + if (trace_syscall(current_tcp, &restart_sig) < 0) { + /* + * ptrace() failed in trace_syscall(). + * Likely a result of process disappearing mid-flight. + * Observed case: exit_group() or SIGKILL terminating + * all processes in thread group. + * We assume that ptrace error was caused by process death. + * We used to detach(current_tcp) here, but since we no longer + * implement "detach before death" policy/hack, + * we can let this process to report its death to us + * normally, via WIFEXITED or WIFSIGNALED wait status. + */ + return true; + } + break; + + case TE_SIGNAL_DELIVERY_STOP: + restart_sig = WSTOPSIG(*pstatus); + print_stopped(current_tcp, si, restart_sig); + break; + + case TE_SIGNALLED: + print_signalled(current_tcp, current_tcp->pid, *pstatus); + droptcb(current_tcp); + return true; + + case TE_GROUP_STOP: + restart_sig = WSTOPSIG(*pstatus); + print_stopped(current_tcp, NULL, restart_sig); if (use_seize) { /* * This ends ptrace-stop, but does *not* end group-stop. - * This makes stopping signals work properly on straced process - * (that is, process really stops. It used to continue to run). + * This makes stopping signals work properly on straced + * process (that is, process really stops. It used to + * continue to run). */ - if (ptrace_restart(PTRACE_LISTEN, tcp, 0) < 0) { - /* Note: ptrace_restart emitted error message */ - exit_code = 1; - return false; - } - return true; + restart_op = PTRACE_LISTEN; + restart_sig = 0; } - /* We don't have PTRACE_LISTEN support... */ - goto restart_tracee; - } + break; - /* We handled quick cases, we are permitted to interrupt now. */ - if (interrupted) - return false; + case TE_EXITED: + print_exited(current_tcp, current_tcp->pid, *pstatus); + droptcb(current_tcp); + return true; - /* - * This should be syscall entry or exit. - * Handle it. - */ - sig = 0; - if (trace_syscall(tcp, &sig) < 0) { + case TE_STOP_BEFORE_EXECVE: /* - * ptrace() failed in trace_syscall(). - * Likely a result of process disappearing mid-flight. - * Observed case: exit_group() or SIGKILL terminating - * all processes in thread group. - * We assume that ptrace error was caused by process death. - * We used to detach(tcp) here, but since we no longer - * implement "detach before death" policy/hack, - * we can let this process to report its death to us - * normally, via WIFEXITED or WIFSIGNALED wait status. + * Under Linux, execve changes pid to thread leader's pid, + * and we see this changed pid on EVENT_EXEC and later, + * execve sysexit. Leader "disappears" without exit + * notification. Let user know that, drop leader's tcb, + * and fix up pid in execve thread's tcb. + * Effectively, execve thread's tcb replaces leader's tcb. + * + * BTW, leader is 'stuck undead' (doesn't report WIFEXITED + * on exit syscall) in multithreaded programs exactly + * in order to handle this case. + * + * PTRACE_GETEVENTMSG returns old pid starting from Linux 3.0. + * On 2.6 and earlier, it can return garbage. */ - return true; + if (os_release >= KERNEL_VERSION(3,0,0)) + current_tcp = maybe_switch_tcbs(current_tcp, current_tcp->pid); + + if (detach_on_execve) { + if (current_tcp->flags & TCB_SKIP_DETACH_ON_FIRST_EXEC) { + current_tcp->flags &= ~TCB_SKIP_DETACH_ON_FIRST_EXEC; + } else { + detach(current_tcp); /* do "-b execve" thingy */ + return true; + } + } + break; + + case TE_STOP_BEFORE_EXIT: + print_event_exit(current_tcp); + break; } - goto restart_tracee; -restart_tracee_with_sig_0: - sig = 0; + /* We handled quick cases, we are permitted to interrupt now. */ + if (interrupted) + return false; -restart_tracee: - if (ptrace_restart(PTRACE_SYSCALL, tcp, sig) < 0) { + if (ptrace_restart(restart_op, current_tcp, restart_sig) < 0) { /* Note: ptrace_restart emitted error message */ exit_code = 1; return false; } - return true; } @@ -2523,7 +2592,9 @@ main(int argc, char *argv[]) exit_code = !nprocs; - while (trace()) + int status; + siginfo_t si; + while (dispatch_event(next_event(&status, &si), &status, &si)) ; cleanup(); -- 2.10.2 ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Strace-devel mailing list Strace-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/strace-devel