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Get rid of TCB_SIGTRAPPED

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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>
This commit is contained in:
Denys Vlasenko 2012-01-18 16:30:47 +01:00
parent 5e09d77500
commit 023b7700de
3 changed files with 3 additions and 59 deletions
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1
defs.h
View File

@ -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

52
signal.c
View File

@ -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;

9
strace.c
View File

@ -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;