E.16 Memory Map Format

To be able to write into flash memory, GDB needs to obtain a memory map from the target. This section describes the format of the memory map.

The memory map is obtained using the ‘qXfer:memory-map:read’ (see qXfer memory map read) packet and is an XML document that lists memory regions.

GDB must be linked with the Expat library to support XML memory maps. See Expat.

The top-level structure of the document is shown below:

<?xml version="1.0"?>
<!DOCTYPE memory-map
          PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
                 "http://sourceware.org/gdb/gdb-memory-map.dtd">
<memory-map>
    region...
</memory-map>

Each region can be either:

• A region of RAM starting at addr and extending for length bytes from there:

  <memory type="ram" start="addr" length="length"/>
  

• A region of read-only memory:

  <memory type="rom" start="addr" length="length"/>
  

• A region of flash memory, with erasure blocks blocksize bytes in length:

  <memory type="flash" start="addr" length="length">
    <property name="blocksize">blocksize</property>
  </memory>
  

Regions must not overlap. GDB assumes that areas of memory not covered by the memory map are RAM, and uses the ordinary ‘M’ and ‘X’ packets to write to addresses in such ranges.

The formal DTD for memory map format is given below:

<!-- ................................................... -->
<!-- Memory Map XML DTD ................................ -->
<!-- File: memory-map.dtd .............................. -->
<!-- .................................... .............. -->
<!-- memory-map.dtd -->
<!-- memory-map: Root element with versioning -->
<!ELEMENT memory-map (memory)*>
<!ATTLIST memory-map    version CDATA   #FIXED  "1.0.0">
<!ELEMENT memory (property)*>
<!-- memory: Specifies a memory region,
             and its type, or device. -->
<!ATTLIST memory        type    (ram|rom|flash) #REQUIRED
                        start   CDATA   #REQUIRED
                        length  CDATA   #REQUIRED>
<!-- property: Generic attribute tag -->
<!ELEMENT property (#PCDATA | property)*>
<!ATTLIST property      name    (blocksize) #REQUIRED>