Memory Ports in Guile (Debugging with GDB)

23.4.3.24 Memory Ports in Guile

GDB provides a port interface to target memory. This allows Guile code to read/write target memory using Guile’s port and bytevector functionality. The main routine is open-memory which returns a port object. One can then read/write memory using that object.

Scheme Procedure: open-memory [#:mode mode] [#:start address] [#:size size]

Return a port object that can be used for reading and writing memory. The port will be open according to mode, which is the standard mode argument to Guile port open routines, except that the ‘"a"’ and ‘"l"’ modes are not supported. See File Ports in GNU Guile Reference Manual. The ‘"b"’ (binary) character may be present, but is ignored: memory ports are binary only. If ‘"0"’ is appended then the port is marked as unbuffered. The default is ‘"r"’, read-only and buffered.

The chunk of memory that can be accessed can be bounded. If both start and size are unspecified, all of memory can be accessed. If only start is specified, all of memory from that point on can be accessed. If only size if specified, all memory in the range [0,size) can be accessed. If both are specified, all memory in the rane [start,start+size) can be accessed.

Scheme Procedure: memory-port?; Return #t if object is an object of type <gdb:memory-port>. Otherwise return #f.

Scheme Procedure: memory-port-range memory-port; Return the range of <gdb:memory-port> memory-port as a list of two elements: (start end). The range is start to end inclusive.

Scheme Procedure: memory-port-read-buffer-size memory-port

Return the size of the read buffer of <gdb:memory-port> memory-port.

This procedure is deprecated and will be removed in GDB 11. It returns 0 when using Guile 2.2 or later.

Scheme Procedure: set-memory-port-read-buffer-size! memory-port size

Set the size of the read buffer of <gdb:memory-port> memory-port to size. The result is unspecified.

This procedure is deprecated and will be removed in GDB 11. When GDB is built with Guile 2.2 or later, you can call setvbuf instead (see setvbuf in GNU Guile Reference Manual).

Scheme Procedure: memory-port-write-buffer-size memory-port

Return the size of the write buffer of <gdb:memory-port> memory-port.

This procedure is deprecated and will be removed in GDB 11. It returns 0 when GDB is built with Guile 2.2 or later.

Scheme Procedure: set-memory-port-write-buffer-size! memory-port size

Set the size of the write buffer of <gdb:memory-port> memory-port to size. The result is unspecified.

This procedure is deprecated and will be removed in GDB 11. When GDB is built with Guile 2.2 or later, you can call setvbuf instead.

A memory port is closed like any other port, with close-port.

Combined with Guile’s bytevectors, memory ports provide a lot of utility. For example, to fill a buffer of 10 integers in memory, one can do something like the following.

;; In the program: int buffer[10];
(use-modules (rnrs bytevectors))
(use-modules (rnrs io ports))
(define addr (parse-and-eval "buffer"))
(define n 10)
(define byte-size (* n 4))
(define mem-port (open-memory #:mode "r+" #:start
                              (value->integer addr) #:size byte-size))
(define byte-vec (make-bytevector byte-size))
(do ((i 0 (+ i 1)))
    ((>= i n))
    (bytevector-s32-native-set! byte-vec (* i 4) (* i 42)))
(put-bytevector mem-port byte-vec)
(close-port mem-port)