Instruction Syntax

Mnemonic	Format	Description
mtlr	rS	Move to Link Register

Instruction Encoding

Field	Bits	Description
Primary Opcode	0-5	011111 (0x1F)
rS	6-10	Source register
Reserved	11-15	00000
Reserved	16-20	00000
Reserved	21-29	000000000
Reserved	30	0
SPR	31-31	Special Purpose Register (8 = LR)

Operation

LR ← (rS)

The contents of register rS are copied into the Link Register (LR).

Affected Registers

Link Register (LR)

(always)

• Updated with the value from rS

Examples

Basic Move to Link Register

mtlr r3     # Copy value from r3 to LR

Save and Restore Link Register

# Save LR before function call
mflr r10        # Save current LR value
bl function     # Call function (LR gets return address)
mtlr r10        # Restore original LR value

Custom Return Address

# Set custom return address
lis r3, return_addr@ha
addi r3, r3, return_addr@l
mtlr r3         # Set LR to custom return address
blr             # Return to custom address

Function Pointer Return

# Return to address stored in register
mflr r10        # Save original return address
mtlr r3         # Set LR to function pointer address
blr             # Return to function pointer

Exception Handler Setup

# Set up exception handler return
lis r3, handler_return@ha
addi r3, r3, handler_return@l
mtlr r3         # Set LR to handler return address
# ... exception handling code ...
blr             # Return to handler return address

Nested Function Calls

# Handle nested function calls
mflr r10        # Save current return address
bl inner_func   # Call inner function
mtlr r10        # Restore outer function return address
blr             # Return to outer function

Related Instructions

mflr, blr, bclr, b, bl