336b30e58a
Because SIGTTOU is sent to the whole process instead of to a specific thread, consuming a pending SIGTTOU in the destructor of scoped_ignore_sigttou could consume a SIGTTOU signal raised due to actions done by some other thread. Simply avoid sigtimedwait in scoped_ignore_sigttou, thus plugging the race. This works because we know that when the thread writes to the terminal and the signal is blocked, the kernel does not raise the signal at all. Tested on GNU/Linux, Solaris 11 and FreeBSD. gdb/ChangeLog: yyyy-mm-dd Pedro Alves <pedro@palves.net> * scoped_ignore_signal.h (scoped_ignore_signal): Add ConsumePending template parameter. (scoped_ignore_signal::~scoped_ignore_signal): Skip calling sigtimedwait if ConsumePending is false. (scoped_ignore_sigpipe): Initialize with ConsumePending=true. * scoped_ignore_sigttou.h (scoped_ignore_sigttou) <m_ignore_signal>: Initialize with ConsumePending=false. Change-Id: I92f754dbc45c45819dce2ce68b8c067d8d5c61b1
105 lines
2.9 KiB
C++
105 lines
2.9 KiB
C++
/* Support for ignoring signals.
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Copyright (C) 2021 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef SCOPED_IGNORE_SIGNAL_H
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#define SCOPED_IGNORE_SIGNAL_H
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#include <signal.h>
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/* RAII class used to ignore a signal in a scope. If sigprocmask is
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supported, then the signal is only ignored by the calling thread.
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Otherwise, the signal disposition is set to SIG_IGN, which affects
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the whole process. If ConsumePending is true, the destructor
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consumes a pending Sig. SIGPIPE for example is queued on the
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thread even if blocked at the time the pipe is written to. SIGTTOU
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OTOH is not raised at all if the thread writing to the terminal has
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it blocked. Because SIGTTOU is sent to the whole process instead
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of to a specific thread, consuming a pending SIGTTOU in the
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destructor could consume a signal raised due to actions done by
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some other thread. */
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template <int Sig, bool ConsumePending>
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class scoped_ignore_signal
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{
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public:
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scoped_ignore_signal ()
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{
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#ifdef HAVE_SIGPROCMASK
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sigset_t set, old_state;
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sigemptyset (&set);
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sigaddset (&set, Sig);
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sigprocmask (SIG_BLOCK, &set, &old_state);
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m_was_blocked = sigismember (&old_state, Sig);
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#else
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m_osig = signal (Sig, SIG_IGN);
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#endif
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}
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~scoped_ignore_signal ()
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{
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#ifdef HAVE_SIGPROCMASK
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if (!m_was_blocked)
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{
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sigset_t set;
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const timespec zero_timeout = {};
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sigemptyset (&set);
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sigaddset (&set, Sig);
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/* If we got a pending Sig signal, consume it before
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unblocking. */
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if (ConsumePending)
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sigtimedwait (&set, nullptr, &zero_timeout);
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sigprocmask (SIG_UNBLOCK, &set, nullptr);
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}
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#else
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signal (Sig, m_osig);
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#endif
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}
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DISABLE_COPY_AND_ASSIGN (scoped_ignore_signal);
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private:
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#ifdef HAVE_SIGPROCMASK
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bool m_was_blocked;
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#else
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sighandler_t m_osig;
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#endif
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};
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struct scoped_ignore_signal_nop
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{
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/* Note, these can't both be "= default", because otherwise the
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compiler warns that variables of this type are not used. */
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scoped_ignore_signal_nop ()
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{}
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~scoped_ignore_signal_nop ()
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{}
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DISABLE_COPY_AND_ASSIGN (scoped_ignore_signal_nop);
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};
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#ifdef SIGPIPE
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using scoped_ignore_sigpipe = scoped_ignore_signal<SIGPIPE, true>;
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#else
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using scoped_ignore_sigpipe = scoped_ignore_signal_nop;
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#endif
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#endif /* SCOPED_IGNORE_SIGNAL_H */
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