Fix PR breakpoints/16889: gdb segfaults when printing ASM SDT arguments

This commit fixes PR breakpoints/16889, which is about a bug that
triggers when GDB tries to parse probes whose arguments do not contain
the initial (and optional) "N@" part.  For reference sake, the de
facto format is described here:

  <https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation>

Anyway, this PR actually uncovered two bugs (related) that were
happening while parsing the arguments.  The first one was that the
parser *was* catching *some* arguments that were missing the "N@"
part, but it wasn't correctly setting the argument's type.  This was
causing a NULL pointer being dereferenced, ouch...

The second bug uncovered was that the parser was not catching all of
the cases for a probe which did not provide the "N@" part.  The fix
for that was to simplify the check that the code was making to
identify non-prefixed probes.  The code is simpler and easier to read
now.

I am also providing a testcase for this bug, only for x86_64
architectures.

gdb/
2014-05-02  Sergio Durigan Junior  <sergiodj@redhat.com>

	PR breakpoints/16889
	* stap-probe.c (stap_parse_probe_arguments): Simplify
	check for non-prefixed probes (i.e., probes whose
	arguments do not start with "N@").  Always set the
	argument type to a sane value.

gdb/testsuite/
2014-05-02  Sergio Durigan Junior  <sergiodj@redhat.com>

	PR breakpoints/16889
	* gdb.arch/amd64-stap-optional-prefix.S: New file.
	* gdb.arch/amd64-stap-optional-prefix.exp: Likewise.

3 files changed, 95 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 3dac79f..4907abf 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2014-05-02  Sergio Durigan Junior  <sergiodj@redhat.com>
+
+	PR breakpoints/16889
+	* gdb.arch/amd64-stap-optional-prefix.S: New file.
+	* gdb.arch/amd64-stap-optional-prefix.exp: Likewise.
+
 2014-05-01  Pedro Alves  <palves@redhat.com>
 
 	* lib/gdb.exp (gdb_load): Extend comment.  Skip calling
diff --git a/gdb/testsuite/gdb.arch/amd64-stap-optional-prefix.S b/gdb/testsuite/gdb.arch/amd64-stap-optional-prefix.S
new file mode 100644
index 0000000..66689cb
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/amd64-stap-optional-prefix.S
@@ -0,0 +1,32 @@
+/* Copyright (C) 2014 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 <sys/sdt.h>
+
+	.file	"amd64-stap-optional-prefix.S"
+	.text
+	.globl	main
+main:
+	mov	%rsp,%rbp
+	pushq	$42
+	STAP_PROBE1(probe, foo, (%rsp))
+	STAP_PROBE1(probe, bar, -8(%rbp))
+	STAP_PROBE1(probe, foo_prefix, 8@(%rsp))
+	STAP_PROBE1(probe, bar_prefix, 8@-8(%rbp))
+	mov	%rbp,%rsp
+	xor	%rax,%rax
+	ret
diff --git a/gdb/testsuite/gdb.arch/amd64-stap-optional-prefix.exp b/gdb/testsuite/gdb.arch/amd64-stap-optional-prefix.exp
new file mode 100644
index 0000000..cc9d6c3
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/amd64-stap-optional-prefix.exp
@@ -0,0 +1,57 @@
+# Copyright 2014 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/>.
+
+# This testcase is for PR breakpoints/16889
+
+standard_testfile ".S"
+
+if { ![istarget "x86_64-*-*"] } {
+    verbose "Skipping $testfile.exp"
+    return
+}
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile] } {
+    return -1
+}
+
+# Helper procedure to go to probe NAME
+
+proc goto_probe { name } {
+    global decimal hex
+
+    gdb_test "break -pstap $name" "Breakpoint $decimal at $hex"
+    gdb_test "continue" "Breakpoint $decimal, main \\(\\) at .*\r\n.*STAP_PROBE1.*${name},.*\\)"
+}
+
+# Helper procedure to test the probe's argument
+
+proc test_probe_value { value reg_val } {
+    gdb_test "print \$_probe_argc" "= 1"
+    gdb_test "print \$_probe_arg0" "= $value"
+    gdb_test "print \$_probe_arg0 == *((unsigned int *) (${reg_val}))" "= 1"
+}
+
+if { ![runto_main] } {
+    return -1
+}
+
+foreach probe_name [list "foo" "bar" "foo_prefix" "bar_prefix"] \
+    probe_val [list "42" "42" "42" "42"] \
+    probe_reg_val [list "\$rsp" "\$rbp - 8" "\$rsp" "\$rbp - 8"] {
+    with_test_prefix $probe_name {
+	goto_probe $probe_name
+	test_probe_value $probe_val $probe_reg_val
+    }
+}