Re: [PATCH] Partially available/unavailable data in requested range

[Pedro Alves <palves@redhat.com>]

On 04/25/2014 09:48 AM, Yao Qi wrote:

> I thought of this when I wrote this patch.  I was unable to figure
> out your trim-LEN-up trick, and get the code complicated.  Given
> "requesting memory across sections" is a rare case, I didn't go on
> this track further.

Well...

On 04/25/2014 09:48 AM, Yao Qi wrote:
> On 04/25/2014 12:19 AM, Pedro Alves wrote:

>> first_addr_available is clearer than min_addr_available").
> 
> I don't think "first" is clearer than "min".  There are multiple 'M'
> blocks in a traceframe, and the address of some of them are within the
> desired range [OFFSET, OFFSET + LEN).  We are looking for the minimal
> address within the range, instead of the first address within the range.
> For example, supposing we have three 'M' blocks, M1 (0x01 0x02),
> M2 (0x07, 0x08) and M3 (0x4, 0x05), and the requested range is
> [0x03, 0x09), the first 'M' block within this range is M2, while the
> minimal address of 'M' block is M3.  M3 is what we are looking for.

It confused me, because I read "minimal" as in "only barely adequate".
And then we have "maddr", starting with "m", and "M" blocks.  That's a
lot of unrelated 'm's.  I can see now how "first" might be confusing
as well, as leading to think that it's the first we encounter.  Maybe
"low" would be even better:

      /* Records the lowest available address of all blocks that
	 intersects the requested range.  */
      ULONGEST low_addr_available = 0;

> In my patch, there is one more condition check
> 
> 	  if (offset < maddr && maddr < (offset + len))
> 	  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 	    if (min_addr_available == 0 || min_addr_available > maddr)
> 	      min_addr_available = maddr;
> 
> to avoid recoding minimal address *outside* of requested range.  For
> example, we have three 'M' blocks, M1 (0x01 0x02), M2 (0x07, 0x08) and
> M3 (0x04, 0x05), and the requested range is [0x03, 0x09).
> 
>           OFFSET
>           |--- requested ---|
>   |-M1-|    |-M2-|   |-M3-|
> 
> The MIN_ADDR_AVAILABLE is expected to be 0x04 instead of 0x01.

Ah, indeed.

Thanks,
-- 
Pedro Alves