V3: split SEIZE/!SEIZE code paths to reduce confusion.
Extensively comment every possible case.
Verified that all tests/detach* tests work in both SEIZE and !SEIZE
cases.
* strace.c (detach): If PTRACE_SEIZE API is in use, stop the tracee
using PTRACE_INTERRUPT instead of sending it a SIGSTOP.
In a subsequent waitpid loop, correctly wait and suppress SIGSTOP
on detach if PTRACE_INTERRUPT wasn't used, or wait for any ptrace
stop and detach without suppressing signals.
Signed-off-by: Denys Vlasenko <dvlas...@redhat.com>
---
strace.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 76 insertions(+), 13 deletions(-)
diff --git a/strace.c b/strace.c
index 87aad48..5a2f139 100644
--- a/strace.c
+++ b/strace.c
@@ -733,7 +733,7 @@ static int
detach(struct tcb *tcp)
{
int error;
- int status, sigstop_expected;
+ int status, sigstop_expected, interrupt_done;
if (tcp->flags & TCB_BPTSET)
clearbpt(tcp);
@@ -750,6 +750,7 @@ detach(struct tcb *tcp)
error = 0;
sigstop_expected = 0;
+ interrupt_done = 0;
if (tcp->flags & TCB_ATTACHED) {
/*
* We attached but possibly didn't see the expected SIGSTOP.
@@ -757,7 +758,7 @@ detach(struct tcb *tcp)
* would be left stopped (process state T).
*/
sigstop_expected = (tcp->flags & TCB_IGNORE_ONE_SIGSTOP);
- error = ptrace(PTRACE_DETACH, tcp->pid, (char *) 1, 0);
+ error = ptrace(PTRACE_DETACH, tcp->pid, 0, 0);
if (error == 0) {
/* On a clear day, you can see forever. */
}
@@ -765,20 +766,46 @@ detach(struct tcb *tcp)
/* Shouldn't happen. */
perror_msg("detach: ptrace(PTRACE_DETACH, ...)");
}
- else if (my_tkill(tcp->pid, 0) < 0) {
+ else
+ /* ESRCH: process is either not stopped or doesn't exist. */
+ if (my_tkill(tcp->pid, 0) < 0) {
if (errno != ESRCH)
+ /* Shouldn't happen. */
perror_msg("detach: checking sanity");
- }
- else if (!sigstop_expected && my_tkill(tcp->pid, SIGSTOP) < 0) {
- if (errno != ESRCH)
- perror_msg("detach: stopping child");
+ /* else: process doesn't exist. */
}
else
- sigstop_expected = 1;
+ /* Process is not stopped. */
+ if (!sigstop_expected) {
+ /* We need to stop it. */
+ if (use_seize) {
+ /*
+ * With SEIZE, tracee can be in group-stop
already.
+ * In this state sending it another SIGSTOP
does nothing.
+ * Need to use INTERRUPT.
+ * Testcase: trying to ^C a "strace -p
<stopped_process>".
+ */
+ error = ptrace(PTRACE_INTERRUPT, tcp->pid, 0,
0);
+ if (!error)
+ interrupt_done = 1;
+ }
+ else {
+ error = my_tkill(tcp->pid, SIGSTOP);
+ if (!error)
+ sigstop_expected = 1;
+ }
+ if (error && errno != ESRCH) {
+ if (use_seize)
+ perror_msg("detach:
ptrace(PTRACE_INTERRUPT, ...)");
+ else
+ perror_msg("detach: stopping child");
+ }
+ }
}
- if (sigstop_expected) {
+ if (sigstop_expected || interrupt_done) {
for (;;) {
+ int sig;
#ifdef __WALL
if (waitpid(tcp->pid, &status, __WALL) < 0) {
if (errno == ECHILD) /* Already gone. */
@@ -810,13 +837,49 @@ detach(struct tcb *tcp)
/* Au revoir, mon ami. */
break;
}
- if (WSTOPSIG(status) == SIGSTOP) {
+ sig = WSTOPSIG(status);
+ if (debug_flag)
+ fprintf(stderr, "detach wait: event:%d
sig:%d\n",
+ (unsigned)status >> 16, sig);
+ if (sigstop_expected && sig == SIGSTOP) {
+ /* Detach, suppressing SIGSTOP */
ptrace_restart(PTRACE_DETACH, tcp, 0);
break;
}
- error = ptrace_restart(PTRACE_CONT, tcp,
- WSTOPSIG(status) == syscall_trap_sig ? 0
- : WSTOPSIG(status));
+ if (interrupt_done) {
+ unsigned event = (unsigned)status >> 16;
+ if (event == PTRACE_EVENT_STOP /*&& sig ==
SIGTRAP*/) {
+ /*
+ * sig == SIGTRAP: PTRACE_INTERRUPT
stop.
+ * sig == other: process was already
stopped
+ * with this stopping sig (see
tests/detach-stopped).
+ * Looks like re-injecting this sig is
not necessary
+ * in DETACH for the tracee to remain
stopped.
+ */
+ sig = 0;
+ }
+ /*
+ * PTRACE_INTERRUPT is not guaranteed to produce
+ * the above event if other ptrace-stop is
pending.
+ * See tests/detach-sleeping testcase:
+ * strace got SIGINT while tracee is sleeping.
+ * We sent PTRACE_INTERRUPT.
+ * We see syscall exit, not PTRACE_INTERRUPT
stop.
+ * We won't get PTRACE_INTERRUPT stop
+ * if we would CONT now. Need to DETACH.
+ */
+ if (sig == syscall_trap_sig)
+ sig = 0;
+ /* else: not sure in which case we can be here.
+ * Signal stop? Inject it while detaching.
+ */
+ ptrace_restart(PTRACE_DETACH, tcp, sig);
+ break;
+ }
+ if (sig == syscall_trap_sig)
+ sig = 0;
+ /* Can't detach just yet, may need to wait for SIGSTOP
*/
+ error = ptrace_restart(PTRACE_CONT, tcp, sig);
if (error < 0)
break;
}
--
1.8.1.4
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