isync
Instruction Synchronize - 4C 00 01 2C
isync
Instruction Syntax
| Mnemonic | Format | Flags |
| isync | - | - |
Instruction Encoding
0
1
0
0
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
1
0
1
0
| Field | Bits | Description |
| Primary Opcode | 0-5 | 010011 (0x13) |
| Reserved | 6-10 | 00000 |
| Reserved | 11-15 | 00000 |
| Reserved | 16-20 | 00000 |
| XO | 21-30 | 0000010010 (150) |
| Reserved | 31 | 0 |
Operation
Wait for all previous instructions to complete Discard any prefetched instructions following isync Refetch and execute instructions following isync
The instruction synchronize instruction provides an ordering function for instruction execution. It ensures that all instructions preceding the isync instruction complete before any instructions following the isync instruction are executed. Additionally, the isync instruction causes the processor to discard any prefetched instructions and refetch instructions following the isync.
Note: This instruction is essential after cache invalidation operations (like icbi), context changes, or any operation that might affect instruction fetch. It ensures that the processor sees any changes to the instruction stream. The instruction acts as both an execution barrier and an instruction fetch barrier.
Affected Registers
None - This instruction does not affect any registers.
For more information on instruction synchronization see Section 2.1.2, "Instruction Synchronization," in the PowerPC Microprocessor Family: The Programming Environments manual.
Examples
Self-Modifying Code Synchronization
# Complete pattern for self-modifying code lis r3, target_instruction@ha addi r3, r3, target_instruction@l # Modify instruction in memory lis r4, new_instruction@ha addi r4, r4, new_instruction@l lwz r5, 0(r4) # Load new instruction word stw r5, 0(r3) # Store modified instruction # Ensure cache coherency and instruction synchronization dcbst 0, r3 # Flush data cache to memory sync # Ensure store completes icbi 0, r3 # Invalidate instruction cache isync # Synchronize instruction stream # Now safe to execute modified code target_instruction: nop # This instruction was modified
Context Switch Synchronization
# Operating system context switch with proper synchronization # Save current context stmw r14, save_area(r1) # Save registers # Load new context lwz r3, new_msr(r0) # Load new MSR value mtmsr r3 # Change processor state isync # Synchronize after MSR change # Load new context registers lmw r14, new_context(r0) # Load new register values lwz r3, new_pc(r0) # Load new program counter mtlr r3 # Set up return address isync # Synchronize before context switch # Return to new context blr # Jump to new context
Cache Management Sequence
# Comprehensive cache management for dynamic code
lis r3, dynamic_code@ha
addi r3, r3, dynamic_code@l
lwz r4, code_size(r0)
li r5, 0
# Generate new code
generate_code_loop:
# ... code generation logic ...
addi r5, r5, 4 # Next instruction
cmpw r5, r4 # Check if done
blt generate_code_loop
# Complete cache management sequence
li r5, 0
cache_mgmt_loop:
add r6, r3, r5 # Current address
dcbst 0, r6 # Flush data cache
icbi 0, r6 # Invalidate instruction cache
addi r5, r5, 32 # Next cache line
cmpw r5, r4 # Check if done
blt cache_mgmt_loop
sync # Memory barrier
isync # Instruction synchronization
# Now execute generated code
mtctr r3
bcctr 20, 0 # Execute generated code
Exception Handler Installation
# Install new exception handler with proper synchronization lis r3, exception_vector@ha addi r3, r3, exception_vector@l lis r4, new_handler@ha addi r4, r4, new_handler@l # Create branch instruction to new handler sub r5, r4, r3 # Calculate displacement srwi r5, r5, 2 # Convert to word displacement rlwinm r5, r5, 2, 6, 29 # Position in instruction oris r5, r5, 0x4800 # Create branch instruction # Install new exception handler stw r5, 0(r3) # Install branch to handler dcbst 0, r3 # Flush to memory sync # Ensure store completes icbi 0, r3 # Invalidate instruction cache isync # Synchronize instruction stream # Exception handler is now active
MMU Configuration Change
# Change MMU configuration with proper synchronization # Disable interrupts during MMU change mfmsr r3 # Get current MSR rlwinm r4, r3, 0, 17, 15 # Clear interrupt enable bits mtmsr r4 # Disable interrupts isync # Synchronize MSR change # Update page table entries lis r5, page_table@ha addi r5, r5, page_table@l lwz r6, new_mapping(r0) # Load new page mapping stw r6, 0(r5) # Update page table entry # Flush TLB and synchronize tlbie r7 # Invalidate TLB entry sync # Ensure TLB invalidation completes isync # Synchronize instruction stream # Re-enable interrupts mtmsr r3 # Restore original MSR isync # Synchronize MSR change
Performance Counter Reconfiguration
# Reconfigure performance monitoring unit mfspr r3, PMC1 # Read current performance counter lis r4, new_event@ha addi r4, r4, new_event@l lwz r5, 0(r4) # Load new event configuration # Stop performance monitoring li r6, 0 mtspr MMCR0, r6 # Disable performance monitoring isync # Synchronize SPR change # Configure new event mtspr PMC1, r5 # Set new performance counter event isync # Synchronize SPR change # Restart performance monitoring lis r7, mmcr0_enable@ha addi r7, r7, mmcr0_enable@l lwz r8, 0(r7) # Load enable configuration mtspr MMCR0, r8 # Enable performance monitoring isync # Synchronize SPR change
Branch Prediction Reset
# Reset branch prediction after code modification lis r3, modified_branch@ha addi r3, r3, modified_branch@l # Modify branch target lis r4, new_target@ha addi r4, r4, new_target@l sub r5, r4, r3 # Calculate new displacement srwi r5, r5, 2 # Word displacement rlwinm r5, r5, 2, 6, 29 # Position displacement oris r5, r5, 0x4000 # Create conditional branch ori r5, r5, 0x0002 # Add condition bits stw r5, 0(r3) # Update branch instruction # Clear instruction cache and branch prediction dcbst 0, r3 # Flush data cache sync # Ensure store completes icbi 0, r3 # Invalidate instruction cache isync # Clear branch prediction and synchronize # Branch prediction is now reset for this address
Secure Boot Verification
# Secure boot code verification and execution lis r3, boot_code@ha addi r3, r3, boot_code@l lwz r4, code_size(r0) # Verify code integrity bl verify_signature # Verify digital signature cmpwi r3, 0 # Check verification result bne boot_failure # Branch if verification failed # Code is verified, ensure clean execution environment sync # Ensure all pending operations complete icbi 0, r3 # Invalidate instruction cache isync # Synchronize instruction stream # Clear any speculative state li r5, 0 mtctr r5 # Clear count register mtlr r5 # Clear link register isync # Synchronize register changes # Execute verified boot code lis r3, boot_code@ha addi r3, r3, boot_code@l mtctr r3 bcctr 20, 0 # Execute verified code
JIT Compiler Code Installation
# Install JIT compiled code with proper synchronization
lis r3, jit_cache@ha
addi r3, r3, jit_cache@l
lis r4, compiled_method@ha
addi r4, r4, compiled_method@l
lwz r5, method_size(r0)
# Copy compiled method to cache
li r6, 0
copy_method_loop:
lwzx r7, r4, r6 # Load compiled instruction
stwx r7, r3, r6 # Store to JIT cache
addi r6, r6, 4 # Next instruction
cmpw r6, r5 # Check if done
blt copy_method_loop
# Synchronize compiled code installation
li r6, 0
sync_method_loop:
add r7, r3, r6 # Current cache address
dcbst 0, r7 # Flush data cache
icbi 0, r7 # Invalidate instruction cache
addi r6, r6, 32 # Next cache line
cmpw r6, r5 # Check if done
blt sync_method_loop
sync # Memory barrier
isync # Instruction synchronization
# Update method pointer to JIT compiled version
lis r8, method_pointer@ha
addi r8, r8, method_pointer@l
stw r3, 0(r8) # Point to JIT compiled code
dcbst 0, r8 # Ensure pointer update is visible
sync # Memory barrier
isync # Instruction synchronization
Debug Trap Installation and Removal
# Install debug trap with synchronization lis r3, debug_point@ha addi r3, r3, debug_point@l # Save original instruction lwz r4, 0(r3) # Load original instruction stw r4, saved_instr(r0) # Save for later restoration # Install debug trap lis r5, 0x7FE0 # Debug trap instruction ori r5, r5, 0x0008 # Complete trap instruction stw r5, 0(r3) # Install trap # Synchronize trap installation dcbst 0, r3 # Flush data cache sync # Ensure store completes icbi 0, r3 # Invalidate instruction cache isync # Synchronize instruction stream # ... debug session occurs ... # Remove debug trap lwz r4, saved_instr(r0) # Load original instruction stw r4, 0(r3) # Restore original instruction # Synchronize trap removal dcbst 0, r3 # Flush data cache sync # Ensure store completes icbi 0, r3 # Invalidate instruction cache isync # Synchronize instruction stream
Multiprocessor Synchronization Point
# Create synchronization point for multiple processors
lis r3, sync_counter@ha
addi r3, r3, sync_counter@l
lwz r4, processor_count(r0)
# Atomic increment of sync counter
sync_loop:
lwarx r5, 0, r3 # Load with reservation
addi r5, r5, 1 # Increment counter
stwcx. r5, 0, r3 # Store conditional
bne sync_loop # Retry if reservation lost
# Check if all processors have reached sync point
cmpw r5, r4 # Compare with total processor count
bne wait_for_others # Wait if not all processors ready
# All processors ready, proceed with synchronized operation
sync # Memory barrier
isync # Instruction synchronization
# Perform synchronized operation
bl synchronized_operation
# Reset sync counter for next synchronization point
li r6, 0
stw r6, 0(r3) # Reset counter
sync # Ensure reset is visible
isync # Synchronize
wait_for_others:
# Spin wait for other processors
spin_wait:
lwz r7, 0(r3) # Load current counter
cmpw r7, r4 # Check if all ready
bne spin_wait # Continue waiting
sync # Memory barrier
isync # Instruction synchronization
b synchronized_operation