Re: [Qemu-devel] out of bounds in set_cc_op()

[Laurent Vivier]

Le 21/12/2017 à 14:07, Laurent Vivier a écrit :
> Le 21/12/2017 à 13:49, Thomas Huth a écrit :
>> On 20.12.2017 22:56, Paolo Bonzini wrote:
>>> On 20/12/2017 20:20, Peter Maydell wrote:
>>>> On the x86/sanitizer build, new runtime errors:
>>>>   GTESTER check-qtest-m68k
>>>> /home/petmay01/linaro/qemu-for-merges/target/m68k/translate.c:230:12:
>>>> runtime error: index -1 out of bounds for type 'const uint8_t [11]'
>>>>
>>>> ...and similar fails on one or two boards on most of the other
>>>> guest architectures.
>>>
>>> These are preexisting bugs, now exposed by the boot-serial-test.
>>> Thomas, can you identify the architectures that have a problem and
>>> notify the maintainers?  In the meanwhile I'll keep the boot-serial-test
>>> enhancements queued locally, and remove them from the pull request.
>>
>>  Laurent, Richard,
>>
>> looks like old_op is -1 when set_cc_op() is called here for the first
>> time. The problem can be reproduced by running the mini-kernel directly.
>> Just get http://people.redhat.com/~thuth/m68k-uart.bin and run QEMU like
>> this:
>>
>>  qemu-system-m68k -nographic -kernel  ~/tmp/m68k-uart.bin -serial none
>>
>> That kernel only contains these few instructions:
>>
>>   0x41, 0xf9, 0xfc, 0x06, 0x00, 0x00,     /* lea 0xfc060000,%a0 */
>>   0x10, 0x3c, 0x00, 0x54,                 /* move.b #'T',%d0 */
>>   0x11, 0x7c, 0x00, 0x04, 0x00, 0x08,     /* move.b #4,8(%a0) */
>>   0x11, 0x40, 0x00, 0x0c,                 /* move.b %d0,12(%a0) */
>>   0x60, 0xfa                              /* bra.s  loop */
>>
>> The problem occurs during the second instruction (i.e. the first move.b).
>>
>> Do you have any ideas where this -1 in s->cc_op could come from?
> 
> I think it comes from CCOp: it's the value of CC_OP_DYNAMIC.
> 
> We should not use it to access cc_op_live[].
> 
> I try to find a fix, but I think Richard knows this better than me.

This should fix the problem, but I'd like Richard checks it...

diff --git a/target/m68k/translate.c b/target/m68k/translate.c
index b60909222c..721b5801da 100644
--- a/target/m68k/translate.c
+++ b/target/m68k/translate.c
@@ -225,6 +225,11 @@ static void set_cc_op(DisasContext *s, CCOp op)
     s->cc_op = op;
     s->cc_op_synced = 0;

+    if (old_op == CC_OP_DYNAMIC) {
+        tcg_gen_discard_i32(QREG_CC_OP);
+        return;
+    }
+
     /* Discard CC computation that will no longer be used.
        Note that X and N are never dead.  */
     dead = cc_op_live[old_op] & ~cc_op_live[op];


Thanks,
Laurent