Get rid of TCB_SIGTRAPPED

On attempts to block or set SIGTRAP handler,
for example, using sigaction syscall, we generate
an additional SIGSTOP.

This change gets rid of this SIGSTOP sending/ignoring.
It appears to work just fine.

It also works if I force strace to not use PTRACE_O_TRACESYSGOOD,
which means strace stops will be marked with SIGTRAP,
not (SIGTRAP | 0x80) - I wondered maybe that's when
this hack is needed.

So, why we even have TCB_SIGTRAPPED? No one knows. It predates
version control: this code was present in the initial commit,
in 1999. No adequate comments, either.

Moreover, TCB_SIGTRAPPED is not set in sys_rt_sigaction
and sys_sigprocmask syscalls - the ones which are most usually
used to implement signal blocking, it is only set in obsolete
sys_signal, sys_sigaction, sys_sigsetmask, and in some dead
non-Linux code.

I think whatever bug it was fixing is gone long ago -
at least as long as sys_rt_sigaction is used by glibc.
Again, since glibc (and uclibc) uses sys_rt_sigaction
and sys_sigprocmask, modified code paths are not used
by most programs anyway.

* defs.h: Remove definition of TCB_SIGTRAPPED.
* signal.c (sys_sigvec): Don't set TCB_SIGTRAPPED and don't send SIGSTOP.
(sys_sigsetmask): Likewise.
(sys_sigaction): Likewise.
(sys_signal): Likewise.
* strace.c (trace): Remove code which executes if TCB_SIGTRAPPED is set.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>

3 files changed, 3 insertions, 59 deletions

diff --git a/defs.h b/defs.h
index 45e324684..e0b9e5167 100644
--- a/defs.h
+++ b/defs.h
@@ -475,7 +475,6 @@ struct tcb {
 #define TCB_INSYSCALL	00010
 #define TCB_ATTACHED	00020	/* Process is not our own child */
 #define TCB_BPTSET	00100	/* "Breakpoint" set after fork(2) */
-#define TCB_SIGTRAPPED	00200	/* Process wanted to block SIGTRAP */
 #define TCB_REPRINT	01000	/* We should reprint this syscall on exit */
 #define TCB_FILTERED	02000	/* This system call has been filtered out */
 #ifdef LINUX
diff --git a/signal.c b/signal.c
index 999d14925..271d6f27c 100644
--- a/signal.c
+++ b/signal.c
@@ -842,24 +842,12 @@ sys_sigvec(struct tcb *tcp)
 			tprints("{SIG_DFL}");
 			break;
 		case (int) SIG_IGN:
-			if (tcp->u_arg[0] == SIGTRAP) {
-				tcp->flags |= TCB_SIGTRAPPED;
-				kill(tcp->pid, SIGSTOP);
-			}
 			tprints("{SIG_IGN}");
 			break;
 		case (int) SIG_HOLD:
-			if (tcp->u_arg[0] == SIGTRAP) {
-				tcp->flags |= TCB_SIGTRAPPED;
-				kill(tcp->pid, SIGSTOP);
-			}
-			tprints("SIG_HOLD");
+			tprints("{SIG_HOLD}");
 			break;
 		default:
-			if (tcp->u_arg[0] == SIGTRAP) {
-				tcp->flags |= TCB_SIGTRAPPED;
-				kill(tcp->pid, SIGSTOP);
-			}
 			tprintf("{%#lx, ", (unsigned long) sv.sv_handler);
 			printsigmask(&sv.sv_mask, 0);
 			tprints(", ");
@@ -923,14 +911,6 @@ sys_sigsetmask(struct tcb *tcp)
 		sigset_t sigm;
 		long_to_sigset(tcp->u_arg[0], &sigm);
 		printsigmask(&sigm, 0);
-#ifndef USE_PROCFS
-		if ((tcp->u_arg[0] & sigmask(SIGTRAP))) {
-			/* Mark attempt to block SIGTRAP */
-			tcp->flags |= TCB_SIGTRAPPED;
-			/* Send unblockable signal */
-			kill(tcp->pid, SIGSTOP);
-		}
-#endif /* !USE_PROCFS */
 	}
 	else if (!syserror(tcp)) {
 		sigset_t sigm;
@@ -1005,24 +985,10 @@ sys_sigaction(struct tcb *tcp)
 			tprints("{SIG_ERR, ");
 		else if ((long)sa.SA_HANDLER == (long)SIG_DFL)
 			tprints("{SIG_DFL, ");
-		else if ((long)sa.SA_HANDLER == (long)SIG_IGN) {
-#ifndef USE_PROCFS
-			if (tcp->u_arg[0] == SIGTRAP) {
-				tcp->flags |= TCB_SIGTRAPPED;
-				kill(tcp->pid, SIGSTOP);
-			}
-#endif /* !USE_PROCFS */
+		else if ((long)sa.SA_HANDLER == (long)SIG_IGN)
 			tprints("{SIG_IGN, ");
-		}
-		else {
-#ifndef USE_PROCFS
-			if (tcp->u_arg[0] == SIGTRAP) {
-				tcp->flags |= TCB_SIGTRAPPED;
-				kill(tcp->pid, SIGSTOP);
-			}
-#endif /* !USE_PROCFS */
+		else
 			tprintf("{%#lx, ", (long) sa.SA_HANDLER);
-		}
 #ifndef LINUX
 		printsigmask(&sa.sa_mask, 0);
 #else
@@ -1060,21 +1026,9 @@ sys_signal(struct tcb *tcp)
 			tprints("SIG_DFL");
 			break;
 		case (long) SIG_IGN:
-#ifndef USE_PROCFS
-			if (tcp->u_arg[0] == SIGTRAP) {
-				tcp->flags |= TCB_SIGTRAPPED;
-				kill(tcp->pid, SIGSTOP);
-			}
-#endif /* !USE_PROCFS */
 			tprints("SIG_IGN");
 			break;
 		default:
-#ifndef USE_PROCFS
-			if (tcp->u_arg[0] == SIGTRAP) {
-				tcp->flags |= TCB_SIGTRAPPED;
-				kill(tcp->pid, SIGSTOP);
-			}
-#endif /* !USE_PROCFS */
 			tprintf("%#lx", tcp->u_arg[1]);
 		}
 		return 0;
diff --git a/strace.c b/strace.c
index ed7d641a4..f1f634baa 100644
--- a/strace.c
+++ b/strace.c
@@ -2542,15 +2542,6 @@ trace()
 		}
 
 		if (sig != syscall_trap_sig) {
-			if (sig == SIGSTOP &&
-					(tcp->flags & TCB_SIGTRAPPED)) {
-				/*
-				 * Trapped attempt to block SIGTRAP
-				 * Hope we are back in control now.
-				 */
-				tcp->flags &= ~(TCB_INSYSCALL | TCB_SIGTRAPPED);
-				goto restart_tracee_with_sig_0;
-			}
 			if (cflag != CFLAG_ONLY_STATS
 			    && (qual_flags[sig] & QUAL_SIGNAL)) {
 				siginfo_t si;