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Report some ptrace failures; nuke tcp->ptrace_errno

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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>
This commit is contained in:
Denys Vlasenko 2012-03-21 10:32:49 +01:00
parent 907735aec8
commit 235067525c
2 changed files with 22 additions and 16 deletions
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1
defs.h
View File

@ -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

37
strace.c
View File

@ -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;
}