Report some ptrace failures; nuke tcp->ptrace_errno

Report some (not all) ptrace errors, namely,
errors on ptrace restart operations.

Before: 10533 sendto(-1, 0x804895e, 17, 0, NULL, 0 <unfinished ...>
After:  10533 sendto(-1, 0x804895e, 17, 0, NULL, 0 <ptrace(SYSCALL):No such process>

This tells user that strace failed to let sendto syscall
to be entered - process was dead at that point of time.
It is (marginally) better than to always say "<unfinished ...>"

While at it, patch removes tcp->ptrace_errno.
I added it many months ago, and it looks that after all
it is not needed for ptrace error detection: I failed to execute
a single existing code path which is accessible
through that variable only.

* defs.h: Remove struct tcp::ptrace_errno field.
* strace.c (ptrace_restart): Emit message to log on error.
(printleader): Remove "if (printing_tcp->ptrace_errno)..." code.
(trace): Remove !tcp->ptrace_errno check, it's always true.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/defs.h b/defs.h
index 7179c320a2e5e69b4f2c5dd3135fe38845aa4afe..c87b97dfa2741bb3d03470dc28f3814f1068aaa9 100644 (file)
--- a/defs.h
+++ b/defs.h
@@ -316,7 +316,6 @@ struct tcb {
        long long ext_arg[MAX_ARGS];    /* System call arguments */
 #endif
        long u_rval;            /* (first) return value */
-       int ptrace_errno;
 #if SUPPORTED_PERSONALITIES > 1
        int currpers;           /* Personality at the time of scno update */
 #endif

diff --git a/strace.c b/strace.c
index 04efd1e6f53d9edb1cfb835e1bfc740b977dfdb7..ad29bb40003bfe9355032820ed0d16235da7f4bc 100644 (file)
--- a/strace.c
+++ b/strace.c
@@ -352,10 +352,9 @@ ptrace_restart(int op, struct tcb *tcp, int sig)
        errno = 0;
        ptrace(op, tcp->pid, (void *) 0, (long) sig);
        err = errno;
-       if (!err || err == ESRCH)
+       if (!err)
                return 0;
 
-       tcp->ptrace_errno = err;
        msg = "SYSCALL";
        if (op == PTRACE_CONT)
                msg = "CONT";
@@ -365,6 +364,22 @@ ptrace_restart(int op, struct tcb *tcp, int sig)
        if (op == PTRACE_LISTEN)
                msg = "LISTEN";
 #endif
+       /*
+        * Why curcol != 0? Otherwise sometimes we get this:
+        *
+        * 10252 kill(10253, SIGKILL)              = 0
+        *  <ptrace(SYSCALL,10252):No such process>10253 ...next decode...
+        *
+        * 10252 died after we retrieved syscall exit data,
+        * but before we tried to restart it. Log looks ugly.
+        */
+       if (curcol != 0) {
+               tprintf(" <ptrace(%s):%s>\n", msg, strerror(err));
+               line_ended();
+       }
+       if (err == ESRCH)
+               return 0;
+       errno = err;
        perror_msg("ptrace(PTRACE_%s,pid:%d,sig:%d)", msg, tcp->pid, sig);
        return -1;
 }
@@ -537,15 +552,6 @@ printleader(struct tcb *tcp)
        if (printing_tcp) {
                outf = printing_tcp->outf;
                curcol = printing_tcp->curcol;
-               if (printing_tcp->ptrace_errno) {
-                       if (printing_tcp->flags & TCB_INSYSCALL) {
-                               tprints(" <unavailable>) ");
-                               tabto();
-                       }
-                       tprints("= ? <unavailable>\n");
-                       printing_tcp->ptrace_errno = 0;
-                       printing_tcp->curcol = 0;
-               }
                if (printing_tcp->curcol != 0 && (followfork < 2 || printing_tcp == tcp)) {
                        /*
                         * case 1: we have a shared log (i.e. not -ff), and last line
@@ -2164,10 +2170,10 @@ trace(void)
                 * (Or it still can be that pesky post-execve SIGTRAP!)
                 * Handle it.
                 */
-               if (trace_syscall(tcp) < 0 && !tcp->ptrace_errno) {
-                       /* ptrace() failed in trace_syscall() with ESRCH.
+               if (trace_syscall(tcp) < 0) {
+                       /* ptrace() failed in trace_syscall().
                         * Likely a result of process disappearing mid-flight.
-                        * Observed case: exit_group() terminating
+                        * 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
@@ -2182,11 +2188,12 @@ trace(void)
                sig = 0;
  restart_tracee:
                /* Remember current print column before continuing. */
-               tcp->curcol = curcol;
                if (ptrace_restart(PTRACE_SYSCALL, tcp, sig) < 0) {
+                       tcp->curcol = curcol;
                        cleanup();
                        return -1;
                }
+               tcp->curcol = curcol;
        }
        return 0;
 }