Re: Weird reverse problems

[teawater <teawater@gmail.com>]

Hi Marc,

I had reproduced it.

13	     printf("A\n");
(gdb) rn
infrun: clear_proceed_status_thread (process 21364)
infrun: proceed (addr=0xffffffff, signal=144, step=1)
infrun: resume (step=1, signal=0), trap_expected=0
infrun: wait_for_inferior (treat_exec_as_sigtrap=0)
infrun: infwait_normal_state
infrun: TARGET_WAITKIND_STOPPED
infrun: stop_pc = 0xb7f01af8
infrun: stepped into subroutine
infrun: inserting step-resume breakpoint at 0xb7f01980
infrun: resume (step=0, signal=0), trap_expected=0
infrun: prepare_to_wait
infrun: infwait_normal_state
infrun: TARGET_WAITKIND_STOPPED
infrun: stop_pc = 0xb7f01980
infrun: BPSTAT_WHAT_STEP_RESUME
infrun: resume (step=1, signal=0), trap_expected=1
infrun: prepare_to_wait
infrun: infwait_normal_state
infrun: TARGET_WAITKIND_STOPPED
infrun: stop_pc = 0x80482f8
infrun: stepped into subroutine
infrun: inserting step-resume breakpoint at 0x80482f8
infrun: resume (step=0, signal=0), trap_expected=0
infrun: prepare_to_wait
infrun: infwait_normal_state
infrun: TARGET_WAITKIND_STOPPED
infrun: stop_pc = 0x80482f8
infrun: BPSTAT_WHAT_STEP_RESUME
infrun: resume (step=1, signal=0), trap_expected=1
infrun: prepare_to_wait
infrun: infwait_normal_state
infrun: TARGET_WAITKIND_STOPPED
infrun: stop_pc = 0x80483dc
infrun: keep going
infrun: resume (step=1, signal=0), trap_expected=0
infrun: prepare_to_wait
infrun: infwait_normal_state
infrun: TARGET_WAITKIND_STOPPED
infrun: stop_pc = 0x80483d5
infrun: stepping inside range [0x80483d5-0x80483e1]
infrun: stop_stepping
11	   sleep(0);//3
(gdb)



I think this is a bug of reverse code in infrun.c.  That is because it
deal with plt not very well.

Michael, could you please take a look at this bug?
And I will try to deal with it too. :)

Thanks,
Hui

On Thu, Jan 22, 2009 at 02:52, Marc Khouzam <marc.khouzam@ericsson.com> wrote:
> Hi,
>
> so I'm trying Reverse Debugging by having applied teawater's patches
> on top of HEAD which contains Michael S reverse infrastructure.
>
> I ran into some bizarre behavior when reverse stepping.
> I found that with (I'm guessing) library functions, a reverse next
> will skip a line.  If you look at the simple session I ran below
> (a bit long, but very simple) you can see that on the reverse,
> every two printf gets skipped.
> Also, on a reverse step, multiple sleep() can be skipped.
>
> Weird no?
>
> I tried to look at the code, but performing steps gets pretty
> low level, so I gave up.
>
> Thanks
>
> 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>
> This is free software: you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law.  Type "show
> copying"
> and "show warranty" for details.
> This GDB was configured as "i686-pc-linux-gnu".
> For bug reporting instructions, please see:
> <http://www.gnu.org/software/gdb/bugs/>...
> (gdb) l
> 1       #include <stdio.h>
> 2       #include <unistd.h>
> 3
> 4       int foo(int i) {
> 5           return i;
> 6       }
> 7       int main()
> 8       {
> 9           sleep(0);//1
> 10          sleep(0);//2
> (gdb)
> 11          sleep(0);//3
> 12          sleep(0);//4
> 13          printf("A\n");
> 14          printf("B\n");
> 15          printf("C\n");
> 16          printf("D\n");
> 17          int a = 0;
> 18          a++;
> 19          printf("E\n");
> 20          printf("F\n");
> (gdb)
> 21          printf("G\n");
> 22          printf("H\n");
> 23          return a;
> 24      }
> (gdb) b main
> Breakpoint 1 at 0x80484bd: file a.cc, line 9.
> (gdb) r
> Starting program: /local/home/lmckhou/testing/a.out
>
> Breakpoint 1, main () at a.cc:9
> 9           sleep(0);//1
> (gdb) record
> (gdb) b 24
> Breakpoint 2 at 0x804855b: file a.cc, line 24.
> (gdb) c
> Continuing.
> A
> B
> C
> D
> E
> F
> G
> H
>
> Breakpoint 2, main () at a.cc:24
> 24      }
> (gdb) rn
> 23          return a;
> (gdb) rn
> 21          printf("G\n");    <--- Missed a printf here!
> (gdb) rn
> 19          printf("E\n");    <--- Missed a printf here!
> (gdb) rn
> 18          a++;
> (gdb) rn
> 17          int a = 0;
> (gdb) rn
> 15          printf("C\n");    <--- Missed a printf here!
> (gdb) rn
> 13          printf("A\n");    <--- Missed a printf here!
> (gdb) rn
> 11          sleep(0);//3    <--- Missed a sleep here!
> (gdb) rn
>
> No more reverse-execution history.
> main () at a.cc:9
> 9           sleep(0);//1
> (gdb) n
> 10          sleep(0);//2
> (gdb) n
> 11          sleep(0);//3
> (gdb) n
> 12          sleep(0);//4
> (gdb) n
> 13          printf("A\n");
> (gdb) rs
> 12          sleep(0);//4
> (gdb) rs
> 11          sleep(0);//3
> (gdb) rs
> 10          sleep(0);//2
> (gdb) n
> 11          sleep(0);//3
> (gdb) n
> 12          sleep(0);//4
> (gdb) n
> 13          printf("A\n");
> (gdb) n
> 14          printf("B\n");
> (gdb) n
> 15          printf("C\n");
> (gdb) rs
> 14          printf("B\n");
> (gdb)
>
> No more reverse-execution history.
> main () at a.cc:9
> 9           sleep(0);//1       <--- Woah, missed a bunch of stuff on the
> reverse step!
>
>
>
>