Re: Bug in i386_process_record?

[Michael Snyder <msnyder@vmware.com>]

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);