gdb.info: Memory Region Attributes

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Memory region attributes

"Memory region attributes" allow you to describe special handling
required by regions of your target's memory.  GDB uses attributes to
determine whether to allow certain types of memory accesses; whether to
use specific width accesses; and whether to cache target memory.
   Defined memory regions can be individually enabled and disabled.
When a memory region is disabled, GDB uses the default attributes when
accessing memory in that region.  Similarly, if no memory regions have
been defined, GDB uses the default attributes when accessing all memory.
   When a memory region is defined, it is given a number to identify it;
to enable, disable, or remove a memory region, you specify that number.
`mem LOWER UPPER ATTRIBUTES...'
     Define memory region bounded by LOWER and UPPER with attributes
     ATTRIBUTES....  Note that UPPER == 0 is a special case: it is
     treated as the the target's maximum memory address.  (0xffff on 16
     bit targets, 0xffffffff on 32 bit targets, etc.)
`delete mem NUMS...'
     Remove memory regions NUMS....
`disable mem NUMS...'
     Disable memory regions NUMS....  A disabled memory region is not
     forgotten.  It may be enabled again later.
`enable mem NUMS...'
     Enable memory regions NUMS....
`info mem'
     Print a table of all defined memory regions, with the following
     columns for each region.
    _Memory Region Number_
    _Enabled or Disabled._
          Enabled memory regions are marked with `y'.  Disabled memory
          regions are marked with `n'.
    _Lo Address_
          The address defining the inclusive lower bound of the memory
          region.
    _Hi Address_
          The address defining the exclusive upper bound of the memory
          region.
    _Attributes_
          The list of attributes set for this memory region.

Attributes

Memory Access Mode

The access mode attributes set whether GDB may make read or write
accesses to a memory region.
   While these attributes prevent GDB from performing invalid memory
accesses, they do nothing to prevent the target system, I/O DMA, etc.
from accessing memory.
`ro'
     Memory is read only.
`wo'
     Memory is write only.
`rw'
     Memory is read/write.  This is the default.

Memory Access Size

The acccess size attributes tells GDB to use specific sized accesses in
the memory region.  Often memory mapped device registers require
specific sized accesses.  If no access size attribute is specified, GDB
may use accesses of any size.
`8'
     Use 8 bit memory accesses.
`16'
     Use 16 bit memory accesses.
`32'
     Use 32 bit memory accesses.
`64'
     Use 64 bit memory accesses.

Data Cache

The data cache attributes set whether GDB will cache target memory.
While this generally improves performance by reducing debug protocol
overhead, it can lead to incorrect results because GDB does not know
about volatile variables or memory mapped device registers.
`cache'
     Enable GDB to cache target memory.
`nocache'
     Disable GDB from caching target memory.  This is the default.