[PATCH v3 0/2] Debugging without a symbol file

[PATCH v3 0/2] Debugging without a symbol file

[Luis Machado]

Yet another update to this series.

v3 addresses more comments with both the code itself and the testcase.

Luis Machado (2):
  Debugging without a binary (regression)
  Test GDB connection to GDBserver with no symbol files

 gdb/exec.c                                         | 60 ++++++++++++-
 .../gdb.server/connect-with-no-symbol-file.c       | 22 +++++
 .../gdb.server/connect-with-no-symbol-file.exp     | 97 ++++++++++++++++++++++
 3 files changed, 177 insertions(+), 2 deletions(-)
 create mode 100644 gdb/testsuite/gdb.server/connect-with-no-symbol-file.c
 create mode 100644 gdb/testsuite/gdb.server/connect-with-no-symbol-file.exp

-- 
1.9.1

[PATCH v3 2/2] Test GDB connection to GDBserver with no symbol files

[Luis Machado]

This test exercises the scenarios where we attempt to connect GDB to GDBserver
in standard remote mode, query the symbol file path, attempt to open said
symbol file on GDB's end and fail, causing the connection to drop abruptly.

Regression-tested on x86-64/Ubuntu.

Does it look OK now?

Changes in v2:

- Addressed comments and moved the test to a proc that can be called multiple
times.
- The testcase now exercises these permutations:

* Unreadable file + empty sysroot
* Unreadable file + target: sysroot
* Removed file + empty sysroot
* Removed file + target: sysroot

Changes in v3:

- Simplified testcase source file, removing useless include and printf call.
- Simplified testcase with foreach_with_prefix.

With an unpatched GDB we should see this:

FAIL: gdb.server/connect-with-no-symbol-file.exp: sysroot=: action=permission: connection to GDBserver succeeded (the program is no longer running)
FAIL: gdb.server/connect-with-no-symbol-file.exp: sysroot=: action=delete: connection to GDBserver succeeded (the program is no longer running)
FAIL: gdb.server/connect-with-no-symbol-file.exp: sysroot=target:: action=permission: connection to GDBserver succeeded (the program is no longer running)
FAIL: gdb.server/connect-with-no-symbol-file.exp: sysroot=target:: action=delete: connection to GDBserver succeeded (the program is no longer running)

A patched GDB should have full passes.

gdb/testsuite/ChangeLog:

2016-04-13  Luis Machado  <lgustavo@codesourcery.com>

	* gdb.server/connect-with-no-symbol-file.c: New file.
	* gdb.server/connect-with-no-symbol-file.exp: New file.
---
 .../gdb.server/connect-with-no-symbol-file.c       | 22 +++++
 .../gdb.server/connect-with-no-symbol-file.exp     | 97 ++++++++++++++++++++++
 2 files changed, 119 insertions(+)
 create mode 100644 gdb/testsuite/gdb.server/connect-with-no-symbol-file.c
 create mode 100644 gdb/testsuite/gdb.server/connect-with-no-symbol-file.exp

diff --git a/gdb/testsuite/gdb.server/connect-with-no-symbol-file.c b/gdb/testsuite/gdb.server/connect-with-no-symbol-file.c
new file mode 100644
index 0000000..bb11da2
--- /dev/null
+++ b/gdb/testsuite/gdb.server/connect-with-no-symbol-file.c
@@ -0,0 +1,22 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 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/>.  */
+
+int
+main (int argc, char **argv)
+{
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.server/connect-with-no-symbol-file.exp b/gdb/testsuite/gdb.server/connect-with-no-symbol-file.exp
new file mode 100644
index 0000000..f99e1af
--- /dev/null
+++ b/gdb/testsuite/gdb.server/connect-with-no-symbol-file.exp
@@ -0,0 +1,97 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 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/>.
+
+# Test GDB's ability to properly connect to GDBserver with no pre-opened
+# symbol file.  If GDB is buggy, it will drop the connection when
+# it attempts to open the symbol file indicated by GDBserver and fails.
+#
+# This test is only meaningful for standard remote connections.
+
+load_lib gdbserver-support.exp
+
+standard_testfile
+
+if { [skip_gdbserver_tests] } {
+    return 0
+}
+
+if { [prepare_for_testing $testfile.exp $testfile $srcfile debug] } {
+    return -1
+}
+
+# Test connecting GDB to GDBserver without loading a symbol file.
+#
+# SYSROOT is the desired sysroot string
+#
+# ACTION is the action to perform to the symbol file on the target.
+# It can be either "permission" to deny access to the file or "delete"
+# to remove the file.
+#
+proc connect_no_symbol_file { sysroot action } {
+    global binfile
+
+    with_test_prefix "setup" {
+	# Copy the symbol file to the target.
+	gdb_remote_download target $binfile.bak $binfile 
+
+	# Make sure we're disconnected, in case we're testing with an
+	# extended-remote board, therefore already connected.
+	gdb_test "disconnect" ".*" "disconnect"
+
+	# Discard any symbol files that we have opened.
+	gdb_test "file" ".*" "discard symbol table" \
+	    {Discard symbol table from `.*'\? \(y or n\) } "y"
+
+	# Set sysroot to something non-target and possibly also invalid so that
+	# GDB is unable to open the symbol file.
+	gdb_test_no_output "set sysroot $sysroot" "adjust sysroot"
+
+	set target_exec [gdbserver_download_current_prog]
+
+	# Start GDBserver.
+	set res [gdbserver_start "" $target_exec]
+
+	set gdbserver_protocol [lindex $res 0]
+	set gdbserver_gdbport [lindex $res 1]
+
+	# Perform test actions to the symbol file on the target.
+	if { $action == "delete" } then {
+	  remote_file target delete $binfile
+	} elseif { $action == "permission" } {
+	  remote_spawn target "chmod 000 $binfile"
+	}
+       
+	# Connect to GDBserver.
+	gdb_target_cmd $gdbserver_protocol $gdbserver_gdbport
+    }
+
+    # Check if GDB succeeded connecting to GDBserver by attempting to detach
+    # from the process.
+    gdb_test "detach" \
+	".*Detaching from program: , process.*Ending remote debugging.*" \
+	"connection to GDBserver succeeded"
+}
+
+# Make sure we have the original symbol file in a safe place to copy from.
+gdb_remote_download host $binfile $binfile.bak
+
+# Run the test with different permutations.
+foreach_with_prefix sysroot {"" "target:"} {
+    foreach_with_prefix action {"permission" "delete"} {
+	connect_no_symbol_file $sysroot $action
+    }
+}
-- 
1.9.1

[PATCH v3 1/2] Debugging without a binary (regression)

[Luis Machado]

When we attempt to debug a process using GDBserver in standard remote mode
without a symbol file on GDB's end, we may run into an issue where GDB cuts
the connection attempt short due to an error. The error is caused by not
being able to open a symbol file, like so:

--

(gdb) set sysroot
(gdb) tar rem :2345
Remote debugging using :2345
/proc/23769/exe: Permission denied.
(gdb) i r
The program has no registers now.
(gdb)

It should've been like this:

(gdb) set sysroot
(gdb) tar rem :2345
Remote debugging using :2345
warning: /tmp/symbol-file: Permission denied.
0xf7ddb2d0 in ?? ()
(gdb) i r
eax            0x0  0
ecx            0x0  0
edx            0x0  0
ebx            0x0  0
esp            0xffffdfa0 0xffffdfa0
ebp            0x0  0x0
esi            0x0  0
edi            0x0  0
eip            0xf7ddb2d0 0xf7ddb2d0
eflags         0x200  [ IF ]
cs             0x33 51
ss             0x2b 43
ds             0x0  0
es             0x0  0
fs             0x0  0
gs             0x0  0
(gdb)

This is caused by a couple of function calls within exec_file_locate_attach
that can potentially throw errors.

The following patch guards both exec_file_attach and symbol_file_add_main to
prevent the errors from disrupting the connection process.

There was also a case where native GDB tripped on this problem, but it was
mostly fixed by bf74e428bca61022bd5cdf6bf28789a184748b4d.

Regression-tested on x86-64/Ubuntu.

Changes in v2:

- We are using two TRY/CATCH blocks to guard both exec_file_attach and
symbol_file_add_main.
- Adjusted code to display only a single warning message if both TRY/CATCH
blocks throw with the same error message.
- I had to duplicate the exception message string because the second CATCH
block will overwrite the contents of the pointer we saved.

Changes in v3:

- Fixed unitialized exception variable.
- Used cleanup to free dynamically-allocated exception message.
- Fixed comment typo.

gdb/ChangeLog:

2016-04-13  Luis Machado  <lgustavo@codesourcery.com>

	* exec.c (exec_file_locate_attach): Guard a couple functions
	that can throw errors.
	(exception_print_same): New helper function.
---
 gdb/exec.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 58 insertions(+), 2 deletions(-)

diff --git a/gdb/exec.c b/gdb/exec.c
index a10ab9b..c998ab1 100644
--- a/gdb/exec.c
+++ b/gdb/exec.c
@@ -135,6 +135,25 @@ exec_file_clear (int from_tty)
     printf_unfiltered (_("No executable file now.\n"));
 }
 
+/* Returns non-zero if exceptions E1 and E2 are equal.  Returns zero
+   otherwise.  */
+
+static int
+exception_print_same (struct gdb_exception e1, struct gdb_exception e2)
+{
+  const char *msg1 = e1.message;
+  const char *msg2 = e2.message;
+
+  if (msg1 == NULL)
+    msg1 = "";
+  if (msg2 == NULL)
+    msg2 = "";
+
+  return (e1.reason == e2.reason
+	  && e1.error == e2.error
+	  && strcmp (e1.message, e2.message) == 0);
+}
+
 /* See gdbcore.h.  */
 
 void
@@ -142,6 +161,7 @@ exec_file_locate_attach (int pid, int from_tty)
 {
   char *exec_file, *full_exec_path = NULL;
   struct cleanup *old_chain;
+  struct gdb_exception prev_err = exception_none;
 
   /* Do nothing if we already have an executable filename.  */
   exec_file = (char *) get_exec_file (0);
@@ -181,9 +201,45 @@ exec_file_locate_attach (int pid, int from_tty)
     }
 
   old_chain = make_cleanup (xfree, full_exec_path);
+  make_cleanup (free_current_contents, &prev_err.message);
+
+  /* exec_file_attach and symbol_file_add_main may throw an error if the file
+     cannot be opened either locally or remotely.
+
+     This happens for example, when the file is first found in the local
+     sysroot (above), and then disappears (a TOCTOU race), or when it doesn't
+     exist in the target filesystem, or when the file does exist, but
+     is not readable.
+
+     Even without a symbol file, the remote-based debugging session should
+     continue normally instead of ending abruptly.  Hence we catch thrown
+     errors/exceptions in the following code.  */
+  TRY
+    {
+      exec_file_attach (full_exec_path, from_tty);
+    }
+  CATCH (err, RETURN_MASK_ERROR)
+    {
+      if (err.message != NULL)
+	warning ("%s", err.message);
+
+      prev_err = err;
+
+      /* Save message so it doesn't get trashed by the catch below.  */
+      prev_err.message = xstrdup (err.message);
+    }
+  END_CATCH
 
-  exec_file_attach (full_exec_path, from_tty);
-  symbol_file_add_main (full_exec_path, from_tty);
+  TRY
+    {
+      symbol_file_add_main (full_exec_path, from_tty);
+    }
+  CATCH (err, RETURN_MASK_ERROR)
+    {
+      if (!exception_print_same (prev_err, err))
+	warning ("%s", err.message);
+    }
+  END_CATCH
 
   do_cleanups (old_chain);
 }
-- 
1.9.1

Re: [PATCH v3 1/2] Debugging without a binary (regression)

[Pedro Alves]

OK.
Thanks,
Pedro Alves

Re: [PATCH v3 2/2] Test GDB connection to GDBserver with no symbol files

[Pedro Alves]

On 04/13/2016 04:53 PM, Luis Machado wrote:
> This test exercises the scenarios where we attempt to connect GDB to GDBserver
> in standard remote mode, query the symbol file path, attempt to open said
> symbol file on GDB's end and fail, causing the connection to drop abruptly.
> 
> Regression-tested on x86-64/Ubuntu.
> 
> Does it look OK now?

Perfect.

Thanks,
Pedro Alves

Re: [PATCH v3 2/2] Test GDB connection to GDBserver with no symbol files

[Luis Machado]

On 04/13/2016 12:38 PM, Pedro Alves wrote:
> On 04/13/2016 04:53 PM, Luis Machado wrote:
>> This test exercises the scenarios where we attempt to connect GDB to GDBserver
>> in standard remote mode, query the symbol file path, attempt to open said
>> symbol file on GDB's end and fail, causing the connection to drop abruptly.
>>
>> Regression-tested on x86-64/Ubuntu.
>>
>> Does it look OK now?
>
> Perfect.
>
> Thanks,
> Pedro Alves
>
>

Thanks. I've pushed this now.

Re: [PATCH v3 2/2] Test GDB connection to GDBserver with no symbol files

[Yao Qi]

Luis Machado <lgustavo@codesourcery.com> writes:

Hi Luis,

> This test exercises the scenarios where we attempt to connect GDB to GDBserver
> in standard remote mode, query the symbol file path, attempt to open said
> symbol file on GDB's end and fail, causing the connection to drop abruptly.
>
> Regression-tested on x86-64/Ubuntu.

Did you see some fails in a real remote testing?  I see some fails in my
cross/remote testing (x86_64 host and arm target),

Running /home/yao/SourceCode/gnu/gdb/git/gdb/testsuite/gdb.server/connect-with-no-symbol-file.exp ...
WARNING: Can`t communicate to remote target.
FAIL: gdb.server/connect-with-no-symbol-file.exp: sysroot=: action=delete: connection to GDBserver succeeded
FAIL: gdb.server/connect-with-no-symbol-file.exp: sysroot=target:: action=permission: connection to GDBserver succeeded

using remote-gdbserver-on-localhost can trigger some fails too,

$ make check RUNTESTFLAGS='--target_board=remote-gdbserver-on-localhost connect-with-no-symbol-file.exp'

-- 
Yao (齐尧)

Re: [PATCH v3 2/2] Test GDB connection to GDBserver with no symbol files

[Luis Machado]

On 04/15/2016 09:06 AM, Yao Qi wrote:
> Luis Machado <lgustavo@codesourcery.com> writes:
>
> Hi Luis,
>
>> This test exercises the scenarios where we attempt to connect GDB to GDBserver
>> in standard remote mode, query the symbol file path, attempt to open said
>> symbol file on GDB's end and fail, causing the connection to drop abruptly.
>>
>> Regression-tested on x86-64/Ubuntu.
>
> Did you see some fails in a real remote testing?  I see some fails in my
> cross/remote testing (x86_64 host and arm target),
>
> Running /home/yao/SourceCode/gnu/gdb/git/gdb/testsuite/gdb.server/connect-with-no-symbol-file.exp ...
> WARNING: Can`t communicate to remote target.
> FAIL: gdb.server/connect-with-no-symbol-file.exp: sysroot=: action=delete: connection to GDBserver succeeded
> FAIL: gdb.server/connect-with-no-symbol-file.exp: sysroot=target:: action=permission: connection to GDBserver succeeded
>
> using remote-gdbserver-on-localhost can trigger some fails too,
>
> $ make check RUNTESTFLAGS='--target_board=remote-gdbserver-on-localhost connect-with-no-symbol-file.exp'
>

No, but let me check this and i'll let you know.

Re: [PATCH v3 2/2] Test GDB connection to GDBserver with no symbol files

[Luis Machado]

On 04/15/2016 09:06 AM, Yao Qi wrote:
> Luis Machado <lgustavo@codesourcery.com> writes:
>
> Hi Luis,
>
>> This test exercises the scenarios where we attempt to connect GDB to GDBserver
>> in standard remote mode, query the symbol file path, attempt to open said
>> symbol file on GDB's end and fail, causing the connection to drop abruptly.
>>
>> Regression-tested on x86-64/Ubuntu.
>
> Did you see some fails in a real remote testing?  I see some fails in my
> cross/remote testing (x86_64 host and arm target),
>
> Running /home/yao/SourceCode/gnu/gdb/git/gdb/testsuite/gdb.server/connect-with-no-symbol-file.exp ...
> WARNING: Can`t communicate to remote target.
> FAIL: gdb.server/connect-with-no-symbol-file.exp: sysroot=: action=delete: connection to GDBserver succeeded
> FAIL: gdb.server/connect-with-no-symbol-file.exp: sysroot=target:: action=permission: connection to GDBserver succeeded
>
> using remote-gdbserver-on-localhost can trigger some fails too,
>
> $ make check RUNTESTFLAGS='--target_board=remote-gdbserver-on-localhost connect-with-no-symbol-file.exp'
>

Do you have a log of the failures or the reason why these fail? They 
seem to be ssh/rsh related.