Process Record and Remote debugging

["Marc Khouzam" <marc dot khouzam at ericsson dot com>]

Hi,

As Process Record and Replay is in the process of being submitted and I
would
really like to see it accepted, I thought it would be useful to report
the small problems I found, while using it.

I was pleasantly surprised to find out I was able to do reverse
debugging 
when attaching to an already running process.  This is great!
 
I then tried remote reverse debugging using gdbserver.  It performed
better
than I expected, but I saw two problems.

1- After you run the 'target' command and are connected to gdbserver, 
the program is considered running; so instead of run, one must use 
continue; that seems to allow for the 'record' command to be used right
away
after the 'target' command.  However, when I do that and then try to 
'continue' Process Record gives an error and the program cannot run.

The workaround is to set a breakpoint on main(), 'continue' and -then-
turn on 'record'.  The error I get is shown in the small session at the
end of the mail.

2- For some reason, when doing remote debugging with record on, when
I step over a printf GDB takes many seconds to come back.  And when I 
tried to step over a malloc, I didn't have the patience to wait for
GDB to come back, it was so long.  Without 'record' it of course works.

Considering I didn't think Process Record worked with attach or remote
debugging, I was very impressed with these finding.

Marc



GNU gdb (GDB) 6.8.50.20090113-cvs
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
<http://gnu.org/licenses/gpl.html>
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This GDB was configured as "i686-pc-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
(gdb) target remote localhost:10008
Remote debugging using localhost:10008
0xb7f9d840 in _start () from /lib/ld-linux.so.2
(gdb) b main
Breakpoint 1 at 0x8048a7f: file ../testapp.cc, line 195.
(gdb) record
(gdb) c
Continuing.
Process record doesn't support instruction rdtsc.
Process record doesn't support instruction 0xf31 at address 0xb7f9dfa7.
0xb7f9dfa7 in _dl_start () from /lib/ld-linux.so.2
Process record: failed to record execution log.