From 023b7700de942f59fcb4cd30903969d276a4d796 Mon Sep 17 00:00:00 2001 From: Denys Vlasenko Date: Wed, 18 Jan 2012 16:30:47 +0100 Subject: [PATCH] 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 --- defs.h | 1 - signal.c | 52 +++------------------------------------------------- strace.c | 9 --------- 3 files changed, 3 insertions(+), 59 deletions(-) diff --git a/defs.h b/defs.h index 45e32468..e0b9e516 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 999d1492..271d6f27 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 ed7d641a..f1f634ba 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; -- 2.40.0