On 04/01/16 20:36, John Snow wrote: > On 01/04/2016 02:15 PM, Mark Cave-Ayland wrote: >> On 04/01/16 19:04, P J P wrote: >> >>> +-- On Mon, 4 Jan 2016, Mark Cave-Ayland wrote --+ >>> | /* Calculate current offset */ >>> | - offset = (int64_t)(s->lba << 11) + s->io_buffer_index; >>> | + offset = ((int64_t)(s->lba) << 11) + s->io_buffer_index; >>> >>> Maybe ((int64_t)s->lba << 11) ? No parenthesis around s->lba. >> >> Yes that works here too (perhaps I was just being over-cautious). >> Alex/John, please let me know if you want me to resubmit. >> > > PJP's version should work just fine. I won't ask you to resubmit, though...
Great, thanks :) > ...But, well, while we're here, I have a question for you: > > So s->lba is an int that we left shift by 11 for a max of (2^43 - 2^11) > then we add it against s->io_buffer_index, a uint64_t, so this statement > could still in theory overflow. > > Except not really, since io_buffer_index is bounded (in general) by > io_buffer_total_len, which is usually (IDE_DMA_BUF_SECTORS*512 + 4) -> > ~132K. > > I don't think there's any rigorous bounds-checking of io_buffer_index, > just ad-hoc checking when we're good enough to remember to do it. And we > don't seem to do it anywhere in macio. Is it worth peppering in an > assert somewhere that io_buffer_index is reasonably small? The DBDMA engine is limited to 16-bit transfers so the maximum transfer size is 64K, and s->io_buffer_index is used to hold the current position within this transfer so unless we get some very large disks I think we should be okay here? ATB, Mark.
