Debugging without a binary (regression)

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 bf74e428bc.

Regression-tested on x86-64/Ubuntu.

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.
This commit is contained in:
Luis Machado 2016-04-13 15:17:22 -05:00
parent b8162e5ac9
commit 57d1de9cf3
2 changed files with 64 additions and 2 deletions

View File

@ -1,3 +1,9 @@
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.
2016-04-13 Pedro Alves <palves@redhat.com>
PR remote/19840

View File

@ -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 (full_exec_path, from_tty);
symbol_file_add_main (full_exec_path, from_tty);
/* 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
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);
}