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

Sergio Durigan Junior
2014-05-02T18:06:27Z

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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

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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
+ }
+}