Re: [Qemu-devel] Re: [PATCH 21/26] Implement TCE translation for sPAPR VIO

[Anthony Liguori <anthony@codemonkey.ws>]

On 03/16/2011 03:05 PM, Benjamin Herrenschmidt wrote:
> On Wed, 2011-03-16 at 17:03 +0100, Alexander Graf wrote:
>>> +int spapr_tce_dma_zero(VIOsPAPRDevice *dev, uint64_t taddr,
>> uint32_t size)
>>> +{
>>> +    uint8_t *zeroes;
>>> +
>>> +#ifdef DEBUG_TCE
>>> +    fprintf(stderr, "spapr_tce_dma_zero taddr=0x%llx size=0x%x\n",
>>> +            (unsigned long long)taddr, size);
>>> +#endif
>>> +
>>> +    /* FIXME: do this better... */
>>> +    zeroes = alloca(size);
>>> +    memset(zeroes, 0, size);
>> You sure that zeroes is still alive during the call? If I were a
>> compiler, I'd probably optimize the return away so that it'd end up
>> being a simple branch to spapr_tce_dma_write - coincidentally
>> invalidating the stack that zeroes is on.
> Ugh ? How would this ever be legal for a compiler to do that ?

But BTW, if you're already being evil and using alloca, it's a whole lot 
nicer to just do:

uint8_t zeros[size];

Regards,

Anthony Liguori

> Ben.
>
>
>