Code for dynamically patching or1k l.j functions....

or1k-j-ops.c

/*
 * l.j instruction is opcode 0 and does a
 * PC ←  exts(Immediate << 2) + JumpInsnAddr
 */

// Top 6 bits is the op code
#define OPENRISC_OPCODE_MASK   	0xfc000000	// Top 6 bits
#define OPENRISC_OPCODE_J 	0x0 << 26
#define OPENRISC_OPCODE_BNF	0x3 << 26
#define OPENRISC_OPCODE_BF	0x4 << 26

static void __patch_reljump_instruction(unsigned int opcode, void* instruction_ptr, void* memory_location)
{
	// Make sure the existing instruction is a jump
	unsigned int existing_instruction = (unsigned int)*instruction_ptr;
	assert((existing_instruction & OPENRISC_OPCODE_MASK) == opcode);
	
	// Work out the distance to jump
	unsigned int jump_from_addr = (unsigned int)instruction_ptr;
	unsigned int jump_to_addr = (unsigned int)memory_location;
	unsigned int jump_delta = jump_to - jump_from;

	// Check the jump_delta fits into the instruction "N" bits.
	assert((jump_delta >> 2) < (2**26));
	*instruction_ptr = opcode | (jump_delta >> 2);
}

#define patch_lj_instruction(instruction_ptr, memory_location) \
	__patch_reljump_instruction(OPENRISC_OPCODE_J, instruction_ptr, memory_location)

#define patch_lbf_instruction(instruction_ptr, memory_location) \
	__patch_reljump_instruction(OPENRISC_OPCODE_BF, instruction_ptr, memory_location)

#define patch_lbnf_instruction(instruction_ptr, memory_location) \
	__patch_reljump_instruction(OPENRISC_OPCODE_BNF, instruction_ptr, memory_location)


static void* extract_jump_location(void* jump_instruction)
{
	unsigned int jump_instruction = *((unsigned int*)(jump_instruction));
	assert((jump_instruction | OPENRISC_OPCODE) == OPENRISC_OPCODE_J);
	unsigned int jump_delta = (~OPENRISC_OPCODE & jump_instruction) << 2;
	return jump_instruction + jump_delta;
}