Re: Bug in i386_process_record?

Hui Zhu
2009-08-10T23:49:38Z

Oops, I will try to find it out.

Thanks,
Hui

On Tue, Aug 11, 2009 at 05:57, Michael Snyder<msnyder@vmware.com> wrote:
> Yes, this seems to be better.  It records only 4 bytes each time
> it is called.
>
> But there seems to be still an off-by-one error?  With the test
> program that I provided, we call memset with an argument of
> 1024, but we actually record 1025 bytes... this code gets hit
> 257 times, with the last time recording only 1 byte.
>
>
>
> Hui Zhu wrote:
>>
>> On Fri, Aug 7, 2009 at 11:39, Michael Snyder<msnyder@vmware.com> wrote:
>>>
>>> Hi Hui,
>>>
>>> While experimenting with your dump/load commands, I think I discovered
>>> a bug in i386_process_record, in the handling of the "string ops"
>>> and the "rep" prefix.  Looks like we are saving the same data over
>>> and over in the log.
>>>
>>> This was made using the attached sample program.
>>>
>>>  (gdb) break main
>>>   Breakpoint 1 at 0x80483c4: file memrange-reverse.c, line 29.
>>>  (gdb) run
>>>   Starting program:
>>>   Breakpoint 1, main ()
>>>   29        memset (blob1, 'a', sizeof (blob1));
>>>  (gdb) record
>>>  (gdb) next
>>>   30        blob1[sizeof (blob1) - 1] = '\0';
>>>  (gdb) record dump
>>>   Saving recording to file 'rec.27255'
>>>   Writing 4-byte magic cookie RECORD_FILE_MAGIC (0x26070920)
>>>  [...]
>>>  Writing register 7 val 0x0000000008049684 (1 plus 8 plus 16 bytes)
>>>  Writing memory 0x08049680 (1 plus 8 plus 8 bytes plus 1024 bytes)
>>>  Writing register 1 val 0x00000000000000ff (1 plus 8 plus 16 bytes)
>>>  Writing register 8 val 0x0000000000587be7 (1 plus 8 plus 16 bytes)
>>>  Writing record_end (1 byte)
>>>  Writing register 7 val 0x0000000008049688 (1 plus 8 plus 16 bytes)
>>>  Writing memory 0x08049684 (1 plus 8 plus 8 bytes plus 1020 bytes)
>>>  Writing register 1 val 0x00000000000000fe (1 plus 8 plus 16 bytes)
>>>  Writing register 8 val 0x0000000000587be7 (1 plus 8 plus 16 bytes)
>>>  Writing record_end (1 byte)
>>>  Writing register 7 val 0x000000000804968c (1 plus 8 plus 16 bytes)
>>>  Writing memory 0x08049688 (1 plus 8 plus 8 bytes plus 1016 bytes)
>>>  Writing register 1 val 0x00000000000000fd (1 plus 8 plus 16 bytes)
>>>  Writing register 8 val 0x0000000000587be7 (1 plus 8 plus 16 bytes)
>>>  Writing record_end (1 byte)
>>>  Writing register 7 val 0x0000000008049690 (1 plus 8 plus 16 bytes)
>>>  Writing memory 0x0804968c (1 plus 8 plus 8 bytes plus 1012 bytes)
>>>  Writing register 1 val 0x00000000000000fc (1 plus 8 plus 16 bytes)
>>>  Writing register 8 val 0x0000000000587be7 (1 plus 8 plus 16 bytes)
>>>  Writing record_end (1 byte)
>>>  Writing register 7 val 0x0000000008049694 (1 plus 8 plus 16 bytes)
>>>  Writing memory 0x08049690 (1 plus 8 plus 8 bytes plus 1008 bytes)
>>>  Writing register 1 val 0x00000000000000fb (1 plus 8 plus 16 bytes)
>>>  Writing register 8 val 0x0000000000587be7 (1 plus 8 plus 16 bytes)
>>>  Writing record_end (1 byte)
>>>  Writing register 7 val 0x0000000008049698 (1 plus 8 plus 16 bytes)
>>>  Writing memory 0x08049694 (1 plus 8 plus 8 bytes plus 1004 bytes)
>>>  Writing register 1 val 0x00000000000000fa (1 plus 8 plus 16 bytes)
>>>  Writing register 8 val 0x0000000000587be7 (1 plus 8 plus 16 bytes)
>>>  Writing record_end (1 byte)
>>>  Writing register 7 val 0x000000000804969c (1 plus 8 plus 16 bytes)
>>>  Writing memory 0x08049698 (1 plus 8 plus 8 bytes plus 1000 bytes)
>>>  Writing register 1 val 0x00000000000000f9 (1 plus 8 plus 16 bytes)
>>>  Writing register 8 val 0x0000000000587be7 (1 plus 8 plus 16 bytes)
>>>  Writing record_end (1 byte)
>>>  Writing register 7 val 0x00000000080496a0 (1 plus 8 plus 16 bytes)
>>>  Writing memory 0x0804969c (1 plus 8 plus 8 bytes plus 996 bytes)
>>>  Writing register 1 val 0x00000000000000f8 (1 plus 8 plus 16 bytes)
>>>  Writing register 8 val 0x0000000000587be7 (1 plus 8 plus 16 bytes)
>>>  [...]
>>>
>>> Altogether there were 256 duplicate entries, each one is
>>> four bytes shorter than the previous one.
>>>
>>>
>>
>> Hi Michael,
>>
>> I reproduce about issue.  This is because "i386_process_record" record
>> rep string insn is not right.
>> I make a patch for it.
>>
>> Please help me review it.
>>
>> Thanks,
>> Hui
>>
>> 2009-08-10  Hui Zhu  <teawater@gmail.com>
>>
>>        * record.c (i386_process_record): Remove some error code.
>>
>> ---
>>  i386-tdep.c |   27 ++++-----------------------
>>  1 file changed, 4 insertions(+), 23 deletions(-)
>>
>> --- a/i386-tdep.c
>> +++ b/i386-tdep.c
>> @@ -4448,9 +4448,8 @@ reswitch:
>>       regcache_raw_read_unsigned (ir.regcache,
>>                                   ir.regmap[X86_RECORD_REDI_REGNUM],
>>                                   &tmpulongest);
>> -      if (!ir.aflag)
>> +      if (ir.aflag)
>>         {
>> -          tmpulongest &= 0xffff;
>>           /* addr += ((uint32_t) read_register (I386_ES_REGNUM)) << 4; */
>>           if (record_debug)
>>             printf_unfiltered (_("Process record ignores the memory change
>> "
>> @@ -4460,27 +4459,9 @@ reswitch:
>>                                paddress (gdbarch, ir.addr));
>>         }
>>       if (prefixes & (PREFIX_REPZ | PREFIX_REPNZ))
>> -        {
>> -          ULONGEST count, eflags;
>> -          regcache_raw_read_unsigned (ir.regcache,
>> -                                      ir.regmap[X86_RECORD_REDI_REGNUM],
>> -                                      &count);
>> -          if (!ir.aflag)
>> -            count &= 0xffff;
>> -          regcache_raw_read_unsigned (ir.regcache,
>> -
>>  ir.regmap[X86_RECORD_EFLAGS_REGNUM],
>> -                                      &eflags);
>> -          if ((eflags >> 10) & 0x1)
>> -            tmpulongest -= (count - 1) * (1 << ir.ot);
>> -          if (record_arch_list_add_mem (tmpulongest, count * (1 <<
>> ir.ot)))
>> -            return -1;
>> -          I386_RECORD_ARCH_LIST_ADD_REG (X86_RECORD_RECX_REGNUM);
>> -        }
>> -      else
>> -        {
>> -          if (record_arch_list_add_mem (tmpulongest, 1 << ir.ot))
>> -            return -1;
>> -        }
>> +        I386_RECORD_ARCH_LIST_ADD_REG (X86_RECORD_RECX_REGNUM);
>> +      if (record_arch_list_add_mem (tmpulongest, 1 << ir.ot))
>> +        return -1;
>>       if (opcode == 0xa4 || opcode == 0xa5)
>>         I386_RECORD_ARCH_LIST_ADD_REG (X86_RECORD_RESI_REGNUM);
>>       I386_RECORD_ARCH_LIST_ADD_REG (X86_RECORD_REDI_REGNUM);
>
>