RE: [PATCH, PR 57748] Check for out of bounds access

[Bernd Edlinger <bernd dot edlinger at hotmail dot de>]

Hi, 

On Tue, 17 Sep 2013 01:09:45, Martin Jambor wrote:
>> @@ -4773,6 +4738,8 @@ expand_assignment (tree to, tree from, b
>>        if (MEM_P (to_rtx)
>>            && GET_MODE (to_rtx) == BLKmode
>>            && GET_MODE (XEXP (to_rtx, 0)) != VOIDmode
>> +          && bitregion_start == 0
>> +          && bitregion_end == 0
>>            && bitsize> 0
>>            && (bitpos % bitsize) == 0
>>            && (bitsize % GET_MODE_ALIGNMENT (mode1)) == 0
>>
> ...
>
> I'm not sure to what extent the hunk adding tests for bitregion_start
> and bitregion_end being zero is connected to this issue. I do not see
> any of the testcases exercising that path. If it is indeed another
> problem, I think it should be submitted (and potentially committed) as
> a separate patch, preferably with a testcase.
>

Meanwhile I am able to give an example where that code is executed
with bitpos = 64, bitsize=32, bitregion_start = 32, bitregion_end = 95.

Afterwards bitpos=0, bitsize=32, which is completely outside
bitregion_start=32, bitregion_end=95.

However this can only be seen in the debugger, as the store_field
goes thru a code path that does not look at bitregion_start/end.

Well that is at least extremely ugly, and I would not be sure, that
I cannot come up with a sample that crashes or creates wrong code.

Currently I think that maybe the best way to fix that would be this:

--- gcc/expr.c    2013-10-21 08:27:09.546035668 +0200
+++ gcc/expr.c    2013-10-22 15:19:56.749476525 +0200
@@ -4762,6 +4762,9 @@ expand_assignment (tree to, tree from, b
           && MEM_ALIGN (to_rtx) == GET_MODE_ALIGNMENT (mode1))
         {
           to_rtx = adjust_address (to_rtx, mode1, bitpos / BITS_PER_UNIT);
+          bitregion_start = 0;
+          if (bitregion_end>= (unsigned HOST_WIDE_INT) bitpos)
+        bitregion_end -= bitpos;
           bitpos = 0;
         }
 
Any suggestions?



Regards
Bernd.

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