Re: [RFA] off by one array reference in i386-low.c/i386_show_dr

Michael Snyder
2011-02-27T21:27:38Z

Jan Kratochvil wrote:
> Hi Michael,
>
> On Sat, 26 Feb 2011 23:52:23 +0100, Michael Snyder wrote:
>> I'm not 100 percent sure this is right, but I do know that
>> as written, it will overflow the array dr_mirror. What do
>> you think?
> [...]
>> --- i386-low.c 1 Jan 2011 15:33:24 -0000 1.5
>> +++ i386-low.c 26 Feb 2011 22:48:38 -0000
> /* A macro to loop over all debug registers. */
> #define ALL_DEBUG_REGISTERS(i) for (i = 0; i < DR_NADDR; i++)
>> @@ -195,7 +195,7 @@ i386_show_dr (struct i386_debug_reg_stat
> ALL_DEBUG_REGISTERS(i)
> {
> printf_unfiltered ("\
>> \tDR%d: addr=0x%s, ref.count=%d DR%d: addr=0x%s, ref.count=%d\n",
>> i, paddress (state->dr_mirror[i]),
>> state->dr_ref_count[i],
>> - i + 1, paddress (state->dr_mirror[i + 1]),
>> + i + 1, paddress (state->dr_mirror[i]),
>> state->dr_ref_count[i + 1]);
>> i++;
>> }
>
> ->
> CONTROL (DR7): 0000000000090101 STATUS (DR6): 0000000000004000
> DR0: addr=0x0000000001c31f30, ref.count=1 DR1: addr=0x0000000000000000, ref.count=0
> DR2: addr=0x0000000000000000, ref.count=0 DR3: addr=0x0000000000000000, ref.count=0
>
> I do not see a bug there; still it could be better commented.

The bug is that when "i" is 3, "i + 1" is 4, and the array only runs
from 0 to 3.