Fix PR19388: Can't access $_siginfo in breakpoint (catch signal) condition

This commit merges both the registers and $_siginfo "thread
running/executing" checks into a single function.

Accessing $_siginfo from a "catch signal" breakpoint condition doesn't
work.  The condition always fails with "Selected thread is running":

 (gdb) catch signal
 Catchpoint 3 (standard signals)
 (gdb)
 condition $bpnum $_siginfo.si_signo == 5
 (gdb) continue
 Continuing.
 Error in testing breakpoint condition:
 Selected thread is running.

 Catchpoint 3 (signal SIGUSR1), 0x0000003615e35877 in __GI_raise (sig=10) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
 56        return INLINE_SYSCALL (tgkill, 3, pid, selftid, sig);
 (gdb)

When accessing the $_siginfo object, we check whether the thread is
marked running (external/public) state and refuse the access if so.
This is so "print $_siginfo" at the prompt fails nicelly when the
current thread is running.  While evaluating breakpoint conditionals,
we haven't decided yet whether the thread is going to stop, so
is_running still returns true, and we thus always error out.

Evaluating an expression that requires registers access is really
conceptually the same -- we could think of $_siginfo as a pseudo
register.  However, in that case we check whether the thread is marked
executing (internal/private state), not running (external/public
state).  Changing the $_siginfo validation to check is_executing as
well fixes the bug in question.

Note that checking is_executing is not fully correct, not even for
registers.  See PR 19389.  However, I think this is the lesser of two
evils and ends up as an improvement.  We at least now have a single
place to fix.

Tested on x86_64 GNU/Linux.

gdb/ChangeLog:
2016-01-13  Pedro Alves  <palves@redhat.com>

	PR breakpoints/19388
	* frame.c (get_current_frame): Use validate_registers_access.
	* gdbthread.h (validate_registers_access): Declare.
	* infrun.c (validate_siginfo_access): Delete.
	(siginfo_value_read, siginfo_value_write): Use
	validate_registers_access.
	* thread.c (validate_registers_access): New function.

gdb/testsuite/ChangeLog:
2016-01-13  Pedro Alves  <palves@redhat.com>

	PR breakpoints/19388
	* gdb.base/catch-signal-siginfo-cond.c: New file.
	* gdb.base/catch-signal-siginfo-cond.exp: New file.

2 files changed, 94 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.base/catch-signal-siginfo-cond.c b/gdb/testsuite/gdb.base/catch-signal-siginfo-cond.c
new file mode 100644
index 0000000..3a9ee3d
--- /dev/null
+++ b/gdb/testsuite/gdb.base/catch-signal-siginfo-cond.c
@@ -0,0 +1,33 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2015-2016 Free Software Foundation, Inc.
+
+   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 <signal.h>
+#include <unistd.h>
+
+void
+handle (int sig)
+{
+}
+
+int
+main (void)
+{
+  signal (SIGUSR1, handle);
+  raise (SIGUSR1);
+  raise (SIGUSR1); /* set breakpoint here */
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/catch-signal-siginfo-cond.exp b/gdb/testsuite/gdb.base/catch-signal-siginfo-cond.exp
new file mode 100644
index 0000000..7fabfd6
--- /dev/null
+++ b/gdb/testsuite/gdb.base/catch-signal-siginfo-cond.exp
@@ -0,0 +1,61 @@
+# Copyright 2015-2016 Free Software Foundation, Inc.
+
+# 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/>.
+
+# Regression test for PR19388.  Make sure we can access $_siginfo in a
+# "catch signal" condition.  A buggy GDB would fail with:
+#
+# (gdb) continue
+# Continuing.
+# Error in testing breakpoint condition:
+# Selected thread is running.
+#
+# Catchpoint 3 (signal SIGUSR1), 0x0000003615e35877 in __GI_raise (sig=10) at raise.c:56
+# 56        return INLINE_SYSCALL (tgkill, 3, pid, selftid, sig);
+# (gdb) FAIL: gdb.base/catch-signal-siginfo-cond.exp: continue
+
+if [target_info exists gdb,nosignals] {
+    verbose "Skipping catch-signal-siginfo-cond.exp because of nosignals."
+    return -1
+}
+
+if { ![supports_get_siginfo_type] } {
+    verbose "Skipping catch-signal-siginfo-cond.exp because of lack of support."
+    return -1
+}
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" "${testfile}" $srcfile {debug}] } {
+    return -1
+}
+
+if ![runto_main] then {
+    fail "Can't run to main"
+    return -1
+}
+
+gdb_breakpoint [gdb_get_line_number "set breakpoint here"]
+
+gdb_test "catch signal"
+
+# It's OK to refer to standard Unix signal numbers 1-15 by number.
+
+# SIGUSR1 == 10.  The catchpoint should not cause a stop.
+gdb_test "condition \$bpnum \$_siginfo.si_signo == 11"
+gdb_test "continue" "set breakpoint here.*" "continue: catchpoint does not trigger"
+
+# This time the catchpoint should cause a stop.
+gdb_test "condition \$bpnum \$_siginfo.si_signo == 10"
+gdb_test "continue" "Catchpoint .*signal SIGUSR1.*" "continue: catchpoint triggers"