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>

diff --git a/defs.h b/defs.h
index 45e32468463aa5e1d276bab9a9f13f3baacaddf0..e0b9e51677070b89f14a5b410346b61bae603426 100644 (file)
--- 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 999d14925e0d03cd71b5e58bb8b7398dfc1930c5..271d6f27c3ea912dc54459cfb019ad66bcc1970e 100644 (file)
--- 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 ed7d641a4ce9cf8583a541d212084edbbfaea08d..f1f634baa67fbd522321b4118c06a3196898ff30 100644 (file)
--- 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;