DE2-115 Ethernet not working

During debugging i.e single stepping, i have noticed that Nios IDE hangs at this line in the above code :

// Create sgdma receive descriptor
	alt_avalon_sgdma_construct_stream_to_mem_desc( &rx_descriptor, &rx_descriptor_end, rx_frame, 0, 0 );

And underneath it says that : warning incompatible pointer types ????

Where as these pointers are defined over here :

// Allocate descriptors in the descriptor_memory (onchip memory)
alt_sgdma_descriptor tx_descriptor		__attribute__ (( section ( ".descriptor_memory" )));
alt_sgdma_descriptor tx_descriptor_end	__attribute__ (( section ( ".descriptor_memory" )));
alt_sgdma_descriptor rx_descriptor  	__attribute__ (( section ( ".descriptor_memory" )));
alt_sgdma_descriptor rx_descriptor_end  __attribute__ (( section ( ".descriptor_memory" )));

I cantt seem to find out where and in which file these are defined ????

i have looked into system.h file and found this :

/*
 * descriptor_memory configuration
 *
 */
# define ALT_MODULE_CLASS_descriptor_memory altera_avalon_onchip_memory2
# define DESCRIPTOR_MEMORY_ALLOW_IN_SYSTEM_MEMORY_CONTENT_EDITOR 0
# define DESCRIPTOR_MEMORY_ALLOW_MRAM_SIM_CONTENTS_ONLY_FILE 0
# define DESCRIPTOR_MEMORY_BASE 0x100000
# define DESCRIPTOR_MEMORY_CONTENTS_INFO ""
# define DESCRIPTOR_MEMORY_DUAL_PORT 0
# define DESCRIPTOR_MEMORY_GUI_RAM_BLOCK_TYPE "AUTO"
# define DESCRIPTOR_MEMORY_INIT_CONTENTS_FILE "DE2115_Ethernet_descriptor_memory"
# define DESCRIPTOR_MEMORY_INIT_MEM_CONTENT 1
# define DESCRIPTOR_MEMORY_INSTANCE_ID "NONE"
# define DESCRIPTOR_MEMORY_IRQ -1
# define DESCRIPTOR_MEMORY_IRQ_INTERRUPT_CONTROLLER_ID -1
# define DESCRIPTOR_MEMORY_NAME "/dev/descriptor_memory"
# define DESCRIPTOR_MEMORY_NON_DEFAULT_INIT_FILE_ENABLED 0
# define DESCRIPTOR_MEMORY_RAM_BLOCK_TYPE "AUTO"
# define DESCRIPTOR_MEMORY_READ_DURING_WRITE_MODE "DONT_CARE"
# define DESCRIPTOR_MEMORY_SINGLE_CLOCK_OP 0
# define DESCRIPTOR_MEMORY_SIZE_MULTIPLE 1
# define DESCRIPTOR_MEMORY_SIZE_VALUE 4096
# define DESCRIPTOR_MEMORY_SPAN 4096
# define DESCRIPTOR_MEMORY_TYPE "altera_avalon_onchip_memory2"
# define DESCRIPTOR_MEMORY_WRITABLE 1

I dont see any dev directory or file with name : DE2115_Ethernet_descriptor_memory , can any one guide me how to remove this warning ????