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Standalone GDB stub

Build

  1. Run make

  2. After successfully building, there are two files to copy into your project: gdbstub.bin and gdbstub.h.

Constraints

The GDB stub has the following constraints:

  1. The binary must reside in read/writable memory.

  2. The sp (r15) register must be properly set.

Loading

Including gdbstub.bin into your project

Depending on how your project is structured, there's a few ways to include gdbstub.bin:

  1. Use the builtin assets linking feature.
# Each asset follows the format: <path>;<symbol>. Duplicates are removed
BUILTIN_ASSETS+= \
	assets/gdbstub.bin;gdbstub_bin
  1. Convert gdbstub.bin into a C array and include that as a source file.
bin2c gdbstub.bin gdbstub_bin gdbstub.bin.h
  1. Load gdbstub.bin from CD.

Initializing gdbstub.bin

Assuming that the following variables:

  • gdbstub_bin is the pointer to the start of the binary, and
  • gdbstub_bin_size is the size (in bytes) of the binary.
  1. Copy the binary over to the load address.
(void)memcpy(GDBSTUB_LOAD_ADDRESS, gdbstub_bin, gdbstub_bin_size);
  1. The driver is the device used to send and receive bytes from/to the GDB stub.
static void
_gdb_device_init(void)
{
        usb_cart_init();
}

static uint8_t
_gdb_device_byte_read(void)
{
        return usb_cart_byte_read();
}

void
_gdb_device_byte_write(uint8_t value)
{
        usb_cart_byte_send(value);
}
  1. Update the driver interface in the GDB stub header.
gdbstub_t * const gdbstub = (gdbstub_t *)gdbstub_bin;

gdbstub->device->init       = _gdb_device_init;
gdbstub->device->byte_read  = _gdb_device_byte_read;
gdbstub->device->byte_write = _gdb_device_byte_write;
  1. Initialize the GDB stub.
gdbstub->init();

Usage

See the GDB example on usage.