Make strace somewhat resilient against process disappearing
under its claws. Prime example is sudden SIGKILL.
Fixes RH#472053
diff --git a/util.c b/util.c
index d64dd84..8f97811 100644
--- a/util.c
+++ b/util.c
@@ -241,6 +241,61 @@
}
/*
+ * Generic ptrace wrapper which tracks ESRCH errors
+ * by setting tcp->ptrace_errno to ESRCH.
+ *
+ * We assume that ESRCH indicates likely process death (SIGKILL?),
+ * modulo bugs where process somehow ended up not stopped.
+ * Unfortunately kernel uses ESRCH for that case too. Oh well.
+ *
+ * Currently used by upeek() only.
+ * TODO: use this in all other ptrace() calls while decoding.
+ */
+long
+do_ptrace(int request, struct tcb *tcp, void *addr, void *data)
+{
+ long l;
+
+ errno = 0;
+ l = ptrace(request, tcp->pid, addr, data);
+ /* Non-ESRCH errors might be our invalid reg/mem accesses,
+ * we do not record them. */
+ if (errno == ESRCH)
+ tcp->ptrace_errno = ESRCH;
+ return l;
+}
+
+/*
+ * Used when we want to unblock stopped traced process.
+ * Should be only used with PTRACE_CONT, PTRACE_DETACH and PTRACE_SYSCALL.
+ * Returns 0 on success or if error was ESRCH
+ * (presumably process was killed while we talk to it).
+ * Otherwise prints error message and returns -1.
+ */
+int
+ptrace_restart(int op, struct tcb *tcp, int sig)
+{
+ int err;
+ const char *msg;
+
+ errno = 0;
+ ptrace(op, tcp->pid, (void *) 1, (void *) (long) sig);
+ err = errno;
+ if (!err || err == ESRCH)
+ return 0;
+
+ tcp->ptrace_errno = err;
+ msg = "SYSCALL";
+ if (op == PTRACE_CONT)
+ msg = "CONT";
+ if (op == PTRACE_DETACH)
+ msg = "DETACH";
+ fprintf(stderr, "strace: ptrace(PTRACE_%s,1,%d): %s\n",
+ msg, sig, strerror(err));
+ return -1;
+}
+
+/*
* Print entry in struct xlat table, if there.
*/
void
@@ -1078,11 +1133,13 @@
}
#endif /* SUNOS4_KERNEL_ARCH_KLUDGE */
errno = 0;
- val = ptrace(PTRACE_PEEKUSER, tcp->pid, (char *) off, 0);
+ val = do_ptrace(PTRACE_PEEKUSER, tcp, (char *) off, 0);
if (val == -1 && errno) {
- char buf[60];
- sprintf(buf,"upeek: ptrace(PTRACE_PEEKUSER,%d,%lu,0)", tcp->pid, off);
- perror(buf);
+ if (errno != ESRCH) {
+ char buf[60];
+ sprintf(buf,"upeek: ptrace(PTRACE_PEEKUSER,%d,%lu,0)", tcp->pid, off);
+ perror(buf);
+ }
return -1;
}
*res = val;