Add a unit test for scoped_ignore_sigpipe

gdb/ChangeLog:
yyyy-mm-dd  Pedro Alves  <pedro@palves.net>

	* Makefile.in (SELFTESTS_SRCS): Add
	unittests/scoped_ignore_signal-selftests.c.
	* unittests/scoped_ignore_signal-selftests.c: New.

Change-Id: Idce24aa9432a3f1eb7065bc9aa030b1d0d7dcad5

gdb/Makefile.in

@@ -461,6 +461,7 @@ SELFTESTS_SRCS = \
 	unittests/mkdir-recursive-selftests.c \
 	unittests/rsp-low-selftests.c \
 	unittests/scoped_fd-selftests.c \
+	unittests/scoped_ignore_signal-selftests.c \
 	unittests/scoped_mmap-selftests.c \
 	unittests/scoped_restore-selftests.c \
 	unittests/search-memory-selftests.c \
@@ -1336,7 +1337,6 @@ HFILES_NO_SRCDIR = \
 	inf-ptrace.h \
 	infcall.h \
 	inferior.h \
-	inflow.h \
 	inline-frame.h \
 	interps.h \
 	jit.h \

gdb/compile/compile.c

@@ -43,7 +43,7 @@
 #include "gdbsupport/gdb_optional.h"
 #include "gdbsupport/gdb_unlinker.h"
 #include "gdbsupport/pathstuff.h"
-#include <signal.h>
+#include "gdbsupport/scoped_ignore_signal.h"
 
 
 
@@ -634,33 +634,6 @@ print_callback (void *ignore, const char *message)
   fputs_filtered (message, gdb_stderr);
 }
 
-/* RAII class used to ignore SIGPIPE in a scope.  */
-
-class scoped_ignore_sigpipe
-{
-public:
-  scoped_ignore_sigpipe ()
-  {
-#ifdef SIGPIPE
-    m_osigpipe = signal (SIGPIPE, SIG_IGN);
-#endif
-  }
-
-  ~scoped_ignore_sigpipe ()
-  {
-#ifdef SIGPIPE
-    signal (SIGPIPE, m_osigpipe);
-#endif
-  }
-
-  DISABLE_COPY_AND_ASSIGN (scoped_ignore_sigpipe);
-
-private:
-#ifdef SIGPIPE
-  sighandler_t m_osigpipe = NULL;
-#endif
-};
-
 /* Process the compilation request.  On success it returns the object
    and source file names.  On an error condition, error () is
    called.  */

gdb/inf-ptrace.c

@@ -20,7 +20,6 @@
 #include "defs.h"
 #include "command.h"
 #include "inferior.h"
-#include "inflow.h"
 #include "terminal.h"
 #include "gdbcore.h"
 #include "regcache.h"

gdb/inflow.c

@@ -29,12 +29,12 @@
 #include <fcntl.h>
 #include "gdbsupport/gdb_select.h"
 
-#include "inflow.h"
 #include "gdbcmd.h"
 #ifdef HAVE_TERMIOS_H
 #include <termios.h>
 #endif
 #include "gdbsupport/job-control.h"
+#include "gdbsupport/scoped_ignore_sigttou.h"
 
 #ifdef HAVE_SYS_IOCTL_H
 #include <sys/ioctl.h>

gdb/procfs.c

@@ -40,7 +40,6 @@
 #include <signal.h>
 #include <ctype.h>
 #include "gdb_bfd.h"
-#include "inflow.h"
 #include "auxv.h"
 #include "procfs.h"
 #include "observable.h"

gdb/ser-unix.c

@@ -32,7 +32,7 @@
 #include "gdbcmd.h"
 #include "gdbsupport/filestuff.h"
 #include <termios.h>
-#include "inflow.h"
+#include "gdbsupport/scoped_ignore_sigttou.h"
 
 struct hardwire_ttystate
   {

gdb/unittests/scoped_ignore_signal-selftests.c

@@ -0,0 +1,125 @@
+/* Self tests for scoped_ignored_signal for GDB, the GNU debugger.
+
+   Copyright (C) 2021 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "defs.h"
+#include "gdbsupport/scoped_ignore_signal.h"
+#include "gdbsupport/selftest.h"
+#include "gdbsupport/scope-exit.h"
+#include <unistd.h>
+#include <signal.h>
+
+namespace selftests {
+namespace scoped_ignore_sig {
+
+#ifdef SIGPIPE
+
+/* True if the SIGPIPE handler ran.  */
+static sig_atomic_t got_sigpipe = 0;
+
+/* SIGPIPE handler for testing.  */
+
+static void
+handle_sigpipe (int)
+{
+  got_sigpipe = 1;
+}
+
+/* Test scoped_ignore_sigpipe.  */
+
+static void
+test_sigpipe ()
+{
+  auto *osig = signal (SIGPIPE, handle_sigpipe);
+  SCOPE_EXIT { signal (SIGPIPE, osig); };
+
+#ifdef HAVE_SIGPROCMASK
+  /* Make sure SIGPIPE isn't blocked.  */
+  sigset_t set, old_state;
+  sigemptyset (&set);
+  sigaddset (&set, SIGPIPE);
+  sigprocmask (SIG_UNBLOCK, &set, &old_state);
+  SCOPE_EXIT { sigprocmask (SIG_SETMASK, &old_state, nullptr); };
+#endif
+
+  /* Create pipe, and close read end so that writes to the pipe fail
+     with EPIPE.  */
+
+  int fd[2];
+  char c = 0xff;
+  int r;
+
+  r = pipe (fd);
+  SELF_CHECK (r == 0);
+
+  close (fd[0]); SCOPE_EXIT { close (fd[1]); };
+
+  /* Check that writing to the pipe results in EPIPE.  EXPECT_SIG
+     indicates whether a SIGPIPE signal is expected.  */
+  auto check_pipe_write = [&] (bool expect_sig)
+  {
+    got_sigpipe = 0;
+    errno = 0;
+
+    r = write (fd[1], &c, 1);
+    SELF_CHECK (r == -1 && errno == EPIPE
+		&& got_sigpipe == expect_sig);
+  };
+
+  /* Check that without a scoped_ignore_sigpipe in scope we indeed get
+     a SIGPIPE signal.  */
+  check_pipe_write (true);
+
+  /* Now check that with a scoped_ignore_sigpipe in scope, SIGPIPE is
+     ignored/blocked.  */
+  {
+    scoped_ignore_sigpipe ignore1;
+
+    check_pipe_write (false);
+
+    /* Check that scoped_ignore_sigpipe nests correctly.  */
+    {
+      scoped_ignore_sigpipe ignore2;
+
+      check_pipe_write (false);
+    }
+
+    /* If nesting works correctly, this write results in no
+       SIGPIPE.  */
+    check_pipe_write (false);
+  }
+
+  /* No scoped_ignore_sigpipe is is scope anymore, so this should
+     result in a SIGPIPE signal.  */
+  check_pipe_write (true);
+}
+
+#endif /* SIGPIPE */
+
+} /* namespace scoped_ignore_sig */
+} /* namespace selftests */
+
+void _initialize_scoped_ignore_signal_selftests ();
+void
+_initialize_scoped_ignore_signal_selftests ()
+{
+#ifdef SIGPIPE
+  selftests::register_test ("scoped_ignore_sigpipe",
+			    selftests::scoped_ignore_sig::test_sigpipe);
+#endif
+}

gdbsupport/scoped_ignore_signal.h

@@ -0,0 +1,97 @@
+/* Support for ignoring signals.
+
+   Copyright (C) 2021 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef SCOPED_IGNORE_SIGNAL_H
+#define SCOPED_IGNORE_SIGNAL_H
+
+#include <signal.h>
+
+/* RAII class used to ignore a signal in a scope.  If sigprocmask is
+   supported, then the signal is only ignored by the calling thread.
+   Otherwise, the signal disposition is set to SIG_IGN, which affects
+   the whole process.  */
+
+template <int Sig>
+class scoped_ignore_signal
+{
+public:
+  scoped_ignore_signal ()
+  {
+#ifdef HAVE_SIGPROCMASK
+    sigset_t set, old_state;
+
+    sigemptyset (&set);
+    sigaddset (&set, Sig);
+    sigprocmask (SIG_BLOCK, &set, &old_state);
+    m_was_blocked = sigismember (&old_state, Sig);
+#else
+    m_osig = signal (Sig, SIG_IGN);
+#endif
+  }
+
+  ~scoped_ignore_signal ()
+  {
+#ifdef HAVE_SIGPROCMASK
+    if (!m_was_blocked)
+      {
+	sigset_t set;
+	const timespec zero_timeout = {};
+
+	sigemptyset (&set);
+	sigaddset (&set, Sig);
+
+	/* If we got a pending Sig signal, consume it before
+	   unblocking.  */
+	sigtimedwait (&set, nullptr, &zero_timeout);
+
+	sigprocmask (SIG_UNBLOCK, &set, nullptr);
+      }
+#else
+    signal (Sig, m_osig);
+#endif
+  }
+
+  DISABLE_COPY_AND_ASSIGN (scoped_ignore_signal);
+
+private:
+#ifdef HAVE_SIGPROCMASK
+  bool m_was_blocked;
+#else
+  sighandler_t m_osig;
+#endif
+};
+
+struct scoped_ignore_signal_nop
+{
+  /* Note, these can't both be "= default", because otherwise the
+     compiler warns that variables of this type are not used.  */
+  scoped_ignore_signal_nop ()
+  {}
+  ~scoped_ignore_signal_nop ()
+  {}
+  DISABLE_COPY_AND_ASSIGN (scoped_ignore_signal_nop);
+};
+
+#ifdef SIGPIPE
+using scoped_ignore_sigpipe = scoped_ignore_signal<SIGPIPE>;
+#else
+using scoped_ignore_sigpipe = scoped_ignore_signal_nop;
+#endif
+
+#endif /* SCOPED_IGNORE_SIGNAL_H */

gdbsupport/scoped_ignore_sigttou.h

@@ -1,4 +1,4 @@
-/* Low level interface to ptrace, for GDB when running under Unix.
+/* Support for signoring SIGTTOU.
 
    Copyright (C) 2003-2021 Free Software Foundation, Inc.
 
@@ -17,40 +17,64 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
-#ifndef INFLOW_H
-#define INFLOW_H
+#ifndef SCOPED_IGNORE_SIGTTOU_H
+#define SCOPED_IGNORE_SIGTTOU_H
 
-#include <unistd.h>
-#include <signal.h>
+#include "gdbsupport/scoped_ignore_signal.h"
 #include "gdbsupport/job-control.h"
 
-/* RAII class used to ignore SIGTTOU in a scope.  */
+#ifdef SIGTTOU
+
+/* Simple wrapper that allows lazy initialization / destruction of T.
+   Slightly more efficient than gdb::optional, because it doesn't
+   carry storage to track whether the object has been initialized.  */
+template<typename T>
+class lazy_init
+{
+public:
+  void emplace ()
+  {
+    new (m_buf) T ();
+  }
+
+  void reset ()
+  {
+    reinterpret_cast <T *> (m_buf)->~T ();
+  }
+
+private:
+  alignas (T) gdb_byte m_buf[sizeof (T)];
+};
+
+/* RAII class used to ignore SIGTTOU in a scope.  This isn't simply
+   scoped_ignore_signal<SIGTTOU> because we want to check the
+   `job_control' global.  */
 
 class scoped_ignore_sigttou
 {
 public:
   scoped_ignore_sigttou ()
   {
-#ifdef SIGTTOU
     if (job_control)
-      m_osigttou = signal (SIGTTOU, SIG_IGN);
-#endif
+      m_ignore_signal.emplace ();
   }
 
   ~scoped_ignore_sigttou ()
   {
-#ifdef SIGTTOU
     if (job_control)
-      signal (SIGTTOU, m_osigttou);
-#endif
+      m_ignore_signal.reset ();
   }
 
   DISABLE_COPY_AND_ASSIGN (scoped_ignore_sigttou);
 
 private:
-#ifdef SIGTTOU
-  sighandler_t m_osigttou = NULL;
-#endif
+  lazy_init<scoped_ignore_signal<SIGTTOU>> m_ignore_signal;
 };
 
-#endif /* inflow.h */
+#else
+
+using scoped_ignore_sigttou = scoped_ignore_signal_nop;
+
+#endif
+
+#endif /* SCOPED_IGNORE_SIGTTOU_H */