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Make threaded execve handling code more reabable and somewhat simpler

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* strace.c (droptcb): Remove outfname check in "outfname && followfork >= 2" -
with recent changes, followfork >= 2 check guarantees that outfile
was specified, and _is already opened_.
(trace): Move tcb existence check before threaded execve handling.
This allows to remove tcp != NULL checks in threaded execve handling.
Rewrite threaded execve handling code to be less indented,
keeping the same logic.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2012-03-22 09:35:51 +01:00
parent 513e9c23df
commit 8511f2a1f0
1 changed files with 67 additions and 66 deletions
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133
strace.c
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@ -684,7 +684,7 @@ droptcb(struct tcb *tcp)
fprintf(stderr, "dropped tcb for pid %d, %d remain\n", tcp->pid, nprocs);
if (tcp->outf) {
if (outfname && followfork >= 2) {
if (followfork >= 2) {
if (tcp->curcol != 0)
fprintf(tcp->outf, " <detached ...>\n");
fclose(tcp->outf);
@ -1898,68 +1898,7 @@ trace(void)
/* Look up 'pid' in our table. */
tcp = pid2tcb(pid);
/* 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 (event == PTRACE_EVENT_EXEC && os_release >= KERNEL_VERSION(3,0,0)) {
long old_pid = 0;
if (ptrace(PTRACE_GETEVENTMSG, pid, NULL, (long) &old_pid) >= 0
&& old_pid > 0
&& old_pid != pid
) {
struct tcb *execve_thread = pid2tcb(old_pid);
if (tcp) {
outf = tcp->outf;
curcol = tcp->curcol;
if (execve_thread) {
if (execve_thread->curcol != 0) {
/*
* One case we are here is -ff:
* try "strace -oLOG -ff test/threaded_execve"
*/
fprintf(execve_thread->outf, " <pid changed to %d ...>\n", pid);
execve_thread->curcol = 0;
}
/* swap output FILEs (needed for -ff) */
tcp->outf = execve_thread->outf;
tcp->curcol = execve_thread->curcol;
execve_thread->outf = outf;
execve_thread->curcol = curcol;
}
droptcb(tcp);
}
tcp = execve_thread;
if (tcp) {
tcp->pid = pid;
if (cflag != CFLAG_ONLY_STATS) {
printleader(tcp);
tprintf("+++ superseded by execve in pid %lu +++\n", old_pid);
line_ended();
tcp->flags |= TCB_REPRINT;
}
}
}
}
if (event == PTRACE_EVENT_EXEC && detach_on_execve) {
if (!skip_startup_execve)
detach(tcp);
/* This was initial execve for "strace PROG". Skip. */
skip_startup_execve = 0;
}
if (tcp == NULL) {
if (!tcp) {
if (followfork) {
/* This is needed to go with the CLONE_PTRACE
changes in process.c/util.c: we might see
@ -1976,17 +1915,79 @@ trace(void)
if (!qflag)
fprintf(stderr, "Process %d attached\n",
pid);
}
else
} else {
/* This can happen if a clone call used
CLONE_PTRACE itself. */
{
if (WIFSTOPPED(status))
ptrace(PTRACE_CONT, pid, (char *) 0, 0);
error_msg_and_die("Unknown pid: %u", pid);
}
}
/* 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 (event == PTRACE_EVENT_EXEC && os_release >= KERNEL_VERSION(3,0,0)) {
struct tcb *execve_thread;
long old_pid = 0;
if (ptrace(PTRACE_GETEVENTMSG, pid, NULL, (long) &old_pid) < 0)
goto dont_switch_tcbs;
if (old_pid <= 0 || old_pid == pid)
goto dont_switch_tcbs;
execve_thread = pid2tcb(old_pid);
/* It should be !NULL, but I feel paranoid */
if (!execve_thread)
goto dont_switch_tcbs;
outf = tcp->outf;
curcol = tcp->curcol;
if (execve_thread->curcol != 0) {
/*
* One case we are here is -ff:
* try "strace -oLOG -ff test/threaded_execve"
*/
fprintf(execve_thread->outf, " <pid changed to %d ...>\n", pid);
execve_thread->curcol = 0;
}
/* Swap output FILEs (needed for -ff) */
tcp->outf = execve_thread->outf;
tcp->curcol = execve_thread->curcol;
/* And their column positions */
execve_thread->outf = outf;
execve_thread->curcol = curcol;
/* Drop leader, but close execve'd thread outfile (if -ff) */
droptcb(tcp);
/* Switch to the thread, reusing leader's outfile and pid */
tcp = execve_thread;
tcp->pid = pid;
if (cflag != CFLAG_ONLY_STATS) {
printleader(tcp);
tprintf("+++ superseded by execve in pid %lu +++\n", old_pid);
line_ended();
tcp->flags |= TCB_REPRINT;
}
}
dont_switch_tcbs:
if (event == PTRACE_EVENT_EXEC && detach_on_execve) {
if (!skip_startup_execve)
detach(tcp);
/* This was initial execve for "strace PROG". Skip. */
skip_startup_execve = 0;
}
/* Set current output file */
outf = tcp->outf;
curcol = tcp->curcol;