[PATCH v2 1/2] Debugging without a binary (regression)
Luis Machado
lgustavo@codesourcery.com
Wed Apr 13 15:16:00 GMT 2016
On 04/13/2016 10:00 AM, Pedro Alves wrote:
> On 04/12/2016 08:24 PM, Luis Machado wrote:
>> 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
>> 0xf7ddb2d0 in ?? ()
>
> The warning output is missing here, right?
>
It is, because i did not update it after the patch. :-)
Should be fixed in v3.
>> (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)
>>
>
>> 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;
>>
>> /* Do nothing if we already have an executable filename. */
>> exec_file = (char *) get_exec_file (0);
>> @@ -182,9 +202,46 @@ exec_file_locate_attach (int pid, int from_tty)
>>
>> old_chain = make_cleanup (xfree, full_exec_path);
>>
>> - 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 problem
>
> "the catch problem below" should be either the "the caught
> problem below", or "the catch below", I think.
>
Yeah, i got things mixed up when coming up with it. "the catch below" is
what i wanted to say.
>> + 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
>>
>> + xfree ((void *) prev_err.message);
>
> This will reference an uninitialized prev_err.message if the
> first TRY doesn't throw. Initialize it with:
>
> struct gdb_exception prev_err = exception_none;
>
>
Done.
> Also, it will leak prev_err.message on Ctrl-C/QUIT, which is
> not caught by RETURN_MASK_ERROR. prev_err.message needs to be
> freed with a cleanup. Say:
>
> struct gdb_exception prev_err = exception_none;
>
> old_chain = make_cleanup (xfree, full_exec_path);
>
> make_cleanup (free_current_contents, &prev_err.message);
>
> TRY
> {
> ...
> }
> CATCH (err, RETURN_MASK_ERROR)
> {
> if (err.message != NULL)
> warning ("%s", err.message);
>
> prev_err = err;
> prev_err.message = xstrdup (err.message);
> }
> ...
>
> do_cleanups (old_chain);
>
Thanks. I've fixed these. I'll get v3 out once the testcase gets reviewed.
> Thanks,
> Pedro Alves
>
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