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

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

On Friday, May 02 2014, I wrote:

> Here's what I am going to push by the end of the day if there are no
> other comments.

Pedro brought something else to my attention: the testcase messages were
not unique, and I could rewrite it in order to make it more
automatized.  So here is the third version that I will push if there are
no other comments.

Thanks,

-- 
Sergio

commit 00412478d10a782e298d9be457a1680cbb6c07c8
Author: Sergio Durigan Junior <sergiodj@redhat.com>
Date:   Thu May 1 18:20:05 2014 -0300

    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/
    2014-05-01  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.arch/amd64-stap-optional-prefix.S: New file.
    	* gdb.arch/amd64-stap-optional-prefix.exp: Likewise.

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..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
+    }
+}