[PATCH 1/2] Fix PR breakpoints/16889: gdb segfaults when printing ASM SDT arguments

[Sergio Durigan Junior <sergiodj at redhat dot com>]

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/
2014-05-01  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/
2014-05-01  Sergio Durigan Junior  <sergiodj@redhat.com>

	PR breakpoints/16889
	* gdb/testsuite/gdb.arch/amd64-stap-optional-prefix.S: New file.
	* gdb/testsuite/gdb.arch/amd64-stap-optional-prefix.exp: Likewise.
---
 gdb/stap-probe.c                                   | 11 ++---
 .../gdb.arch/amd64-stap-optional-prefix.S          | 29 +++++++++++++
 .../gdb.arch/amd64-stap-optional-prefix.exp        | 50 ++++++++++++++++++++++
 3 files changed, 85 insertions(+), 5 deletions(-)
 create mode 100644 gdb/testsuite/gdb.arch/amd64-stap-optional-prefix.S
 create mode 100644 gdb/testsuite/gdb.arch/amd64-stap-optional-prefix.exp

diff --git a/gdb/stap-probe.c b/gdb/stap-probe.c
index dbe9f31..ef45495 100644
--- a/gdb/stap-probe.c
+++ b/gdb/stap-probe.c
@@ -1098,10 +1098,8 @@ stap_parse_probe_arguments (struct stap_probe *probe, struct gdbarch *gdbarch)
 	 Where `N' can be [+,-][4,8].  This is not mandatory, so
 	 we check it here.  If we don't find it, go to the next
 	 state.  */
-      if ((*cur == '-' && cur[1] != '\0' && cur[2] != '@')
-	  && cur[1] != '@')
-	arg.bitness = STAP_ARG_BITNESS_UNDEFINED;
-      else
+      if ((cur[0] == '-' && isdigit (cur[1]) && cur[2] == '@')
+	  || (isdigit (cur[0]) && cur[1] == '@'))
 	{
 	  if (*cur == '-')
 	    {
@@ -1127,11 +1125,14 @@ stap_parse_probe_arguments (struct stap_probe *probe, struct gdbarch *gdbarch)
 	    }
 
 	  arg.bitness = b;
-	  arg.atype = stap_get_expected_argument_type (gdbarch, b);
 
 	  /* Discard the number and the `@' sign.  */
 	  cur += 2;
 	}
+      else
+	arg.bitness = STAP_ARG_BITNESS_UNDEFINED;
+
+      arg.atype = stap_get_expected_argument_type (gdbarch, arg.bitness);
 
       expr = stap_parse_argument (&cur, arg.atype, gdbarch);
 
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..9c86f2d
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/amd64-stap-optional-prefix.S
@@ -0,0 +1,29 @@
+/* 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))
+	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..9747dc8
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/amd64-stap-optional-prefix.exp
@@ -0,0 +1,50 @@
+# 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
+
+if { ![istarget "x86_64-*-*"] } {
+    verbose "Skipping amd64-stap-special-operands.exp"
+    return
+}
+
+standard_testfile ".S"
+
+if { [prepare_for_testing $testfile.exp $testfile $srcfile] } {
+    untested amd64-stap-optional-prefix.exp
+    return -1
+}
+
+# Run to the first probe (foo).
+
+if { ![runto "-pstap foo"] } {
+    fail "run to probe foo"
+    return
+}
+
+# Probe foo's first argument must me == $rsp
+
+gdb_test "print \$_probe_argc" "= 1"
+gdb_test "print \$_probe_arg0" "= 42"
+gdb_test "print \$_probe_arg0 == *((unsigned int *) \$rsp)" "= 1"
+
+# Continuing to the second probe (bar)
+
+gdb_test "break -pstap bar" "Breakpoint $decimal at $hex"
+gdb_test "continue" "Breakpoint $decimal, main \\(\\) at .*\r\n.*STAP_PROBE1.*bar,.*\\)"
+
+gdb_test "print \$_probe_argc" "= 1"
+gdb_test "print \$_probe_arg0" "= 42"
+gdb_test "print \$_probe_arg0 == *((unsigned int *) (\$rbp - 8))" "= 1"
-- 
1.7.11.7