[Lldb-commits] [lldb] [gdbremote] Document MultiMemRead packet in protocol extensions (PR #162675)

[Felipe de Azevedo Piovezan via lldb-commits]

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@@ -735,6 +735,56 @@ This is a performance optimization, which speeds up debugging by avoiding
 multiple round-trips for retrieving thread information. The information from this
 packet can be retrieved using a combination of `qThreadStopInfo` and `m` packets.
 
+### MultiMemRead
+
+Read memory from multiple memory ranges.
+
+This packet has one argument:
+
+* `ranges`: a list of pairs of numbers, formatted in base-16. Each pair is
+separated by a `,`, as is each number in each pair. The first number of the
+pair denotes the base address of the memory read, the second denotes the number
+of bytes to be read. The list must end with a `;`.
+
+The reply packet starts with a comma-separated list of numbers formatted in
+base-16, denoting how many bytes were read from each range, in the same order
+as the request packet. The list is followed by a `;`, followed by a sequence of
+bytes containing binary encoded data for all memory that was read. The length
+of this sequence must be equal to the sum of the numbers provided at the start
----------------
felipepiovezan wrote:

Uhhh, actually you raise a good point. There are a handful of bytes that need to be escaped because of the binary encoding of data  (*). So let's rephrase this as:

> The length of the binary encoded data, after being decoded as required by the GDB remote protocol, is equal to...


(*)
> The binary data representation uses 7d (ASCII ‘}’) as an escape character. Any escaped byte is transmitted as the escape character followed by the original character XORed with 0x20. For example, the byte 0x7d would be transmitted as the two bytes 0x7d 0x5d. The bytes 0x23 (ASCII ‘#’), 0x24 (ASCII ‘$’), and 0x7d (ASCII ‘}’) must always be escaped. Responses sent by the stub must also escape 0x2a (ASCII ‘*’), so that it is not interpreted as the start of a run-length encoded sequence (described next).

https://github.com/llvm/llvm-project/pull/162675