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Re: Bug in i386_process_record?

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);

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