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Re: [PATCH v2 17/19] Fix bit-/byte-offset mismatch in parameter to read_value_memory

On 2017-05-31 16:02, Andreas Arnez wrote:
On Tue, May 30 2017, Simon Marchi wrote:

On 2017-05-09 19:46, Andreas Arnez wrote:
@@ -984,8 +984,9 @@ read_value_memory (struct value *val, LONGEST
       if (status == TARGET_XFER_OK)
 	/* nothing */;
       else if (status == TARGET_XFER_UNAVAILABLE)
-	mark_value_bytes_unavailable (val, embedded_offset + xfered_total,
-				      xfered_partial);
+	mark_value_bits_unavailable (val, (xfered_total * HOST_CHAR_BIT
+					   + bit_offset),
+				     xfered_partial * HOST_CHAR_BIT);

Since it's readily available, please use the unit_size variable here
instead of HOST_CHAR_BIT.

Hm, I thought unit_size represents the number of *bytes* stored at the
same target address.  But we need an offset in *bits* here.  Maybe you
mean that xfered_total should have been multiplied by unit_size even
before my patch?

Ah yes sorry, it should be "* unit_size * 8", since the unit size is specifically the number of 8-bit units.

And yes, the multiplication with unit_size "should" have been there before. In our GDB port that uses 16-bit bytes, we don't really deal with unavailable bytes, so we haven't adapted that particular code. In the end, I don't really mind if you keep "* HOST_CHAR_BIT": if we ever need to deal with unavailable data on a non 8-bit bytes platform, we'll need to adjust many places, so it doesn't really matter if this one uses the unit size or not right now. You can forget about this comment :).

(Is it even correct that xfered_partial measures
addressable target units?  Note that to_xfer_partial is documented to
"[...] transfer up to LEN 8-bit bytes of the target's OBJECT.")

Yes that's the intent, and that's how it is in our GDB port. As for the documentation of to_xfer_partial, that's probably an oversight. target_read and target_write have the right doc.


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