PowerPC ASM Cheatsheet

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Instructions, registers and general info cheatsheet for PowerPC 32-bit Big Endian Assembly architecture used by the Wii U.

How to read this cheatsheet

  • If a right shift operation does not specify it is sign-fill, it is implicitly zero-fill by default
  • If a value is referred to simply as "value" without specifying bit-count, it is implicitly 32 bits (aka a WORD, integer or float depending on context)
  • C-style casts are used due to being shorter to fit in the small table cells code snippets, but treat them as static_cast<T>
  • In most cases where "float" is mentioned in a sentence (not a code snippet where it refers to the type), it usually means "a floating point value" which can be either float or double, not only float.
  • # = placeholder (either a number or a letter, a letter is a labelled placeholder for a number so it may be referenced to by other text)
  • r# = register (shorthand for GPR#)
  • f# = floating point register (shorthand for FPR#)
  • i# = immediate (the subscript numbers next to it is it's size in bits)
  • ui# = unsigned immediate (above is signed)
  • * = unsure of exact functionality
Pseudocode Typedefs
typedef unsigned int   uint;   // 32 bit integer value
typedef signed   int   sint;   // 32 bit integer value
typedef unsigned short ushort; // 16 bit integer value
typedef signed   short sshort; // 16 bit integer value
typedef unsigned char  ubyte;  //  8 bit integer value
typedef signed   char  sbyte;  //  8 bit integer value
                              float;  // 32 bit floating point value
                              double; // 64 bit floating point value

Registers
Register Name Attributes Bits Purpose
General Purpose Registers (GPRs)
r0 GPR0 Volatile + Cross-Module 32 General purpose, may be used by function linkage
r1 GPR1 Saved + Reserved 32 Reserved for storing the stack frame pointer
r2 GPR2 Reserved 32 Reserved for usage by the system
r3 GPR3 Volatile 32 Stores 1st argument passed to function calls and their return value
r4 - r10 GPR4 - GPR10 Volatile 32 Store from 2nd to 8th argument passed to function calls
r11 - r12 GPR11 - GPR12 Volatile + Cross-Module 32 General purpose, may be used by function linkage
r13 GPR13 Reserved 32 Reserved for storing the small data area (SDA) pointer
r14 - r31 GPR14 - GPR31 Saved 32 General purpose, store generic integer values and pointers
Floating Point Registers (FPRs)
f0 FPR0 Volatile 64 Store generic floating point numbers
f1 FPR1 Volatile 64 Stores 1st float argument passed to function calls and their float return value
f2 - f8 FPR2 - FPR8 Volatile 64 Store from 2nd to 8th float argument passed to function calls
f9 - f13 FPR9 - FPR13 Volatile 64 Store generic floating point numbers
f14 - f30 FPR14 - FPR30 Saved 64 Store generic floating point numbers
f31 FPR31 Saved 64 General purpose, used for static chain if needed
Special Purpose Registers (SPRs)
PC / IAR Program Counter / Instruction Address Register Internal 32 Stores the address of the current instruction (Controlled by the CPU)
LR Link Register Volatile 32 Stores the return address for some of the branching instructions
CTR CounT Register Volatile 32 Stores the counter of loop iterations for most instructions that perform loops
CR Condition Register Volatile / Saved 32 Divided in 8 bitfields of 4 bits each to hold different kinds of conditions
XER fiXed point Exception Register Volatile 32 Indicates overflows and carry conditions for integer operations and the number of bytes to be transferred by the load/store string indexed instructions
FPSCR Floating Point Status and Control Register Volatile 32 Contains all floating point exception signal bits, exception summary bits, exception enable bits, and rounding control bits needed for compliance with the IEEE754 floating point arithmetic standard
TB Time Base Special 64 Maintains the time of day and operates interval timers. The TB is not a register itself but the combined value of the two 32-bit registers TBU and TBL.
... There are way more but less common SPRs which won't be listed here - - For a full but undescriptive list of all SPRs, visit wiiubrew.org/Hardware/Espresso
Instructions
Instruction Name Parameters Pseudocode Equivalent Additional Info
add ADD operation rA, rB, rC rA = rB + rC Adds the values of rB and rC together and stores the result in rA
addi ADD Immediate rA, rB, iX₁₆ rA = rB + iX Adds the values of rB and iX together and stores the result in rA
addis ADD Immediate Shifted rA, rB, iX₁₆ rA = rB + (iX << 16) Adds the values of rB and (iX << 16) together and stores the result in rA
and AND Operation rA, rB, rC rA = rB & rC Performs an AND operation on rB and rC then stores the result in rA
andc AND Complement rA, rB, rC rA = rB & ~rC Performs an AND operation on rB and negated rC then stores the result in rA
andi. AND Immediate rA, rB, uiX₁₆ rA = rB & uiX Performs an AND operation on rB and uiX then stores the result in rA
andis. AND Immediate Shifted rA, rB, uiX₁₆ rA = rB & (uiX << 16) Performs an AND operation on rB and (uiX << 16) then stores the result in rA
b Branch iX₂₄ goto LABEL Jumps from the current address to IAR + iX, either up or down
bl Branch and Link iX₂₄ ((void (*)())IAR + iX)() Jumps from the current address to IAR + iX, either up or down

Also stores the address of the instruction directly below it in LR

This is the most common instruction to use for calling a function

blr Branch to Link Register N/A return <r3 / f1> Jumps from the current address to the address stored in LR

This is essentially the return statement of a function, with the value currently loaded into either r3 or f1 holding the returned value, depending on if the return type is a fixed or floating point value

beq Branch if EQual iX₂₄ if (x == y) goto LABEL If the EQ bit in CR0 is 1, jumps from the current address to IAR + iX

Otherwise, does nothing

bne Branch if Not Equal iX₂₄ if (x != y) goto LABEL If the EQ bit in CR0 is 0, jumps from the current address to IAR + iX

Otherwise, does nothing

bgt Branch if Greater Than iX₂₄ if (x > y) goto LABEL If the GT bit in CR0 is 1, jumps from the current address to IAR + iX

Otherwise, does nothing

blt Branch if Less Than iX₂₄ if (x < y) goto LABEL If the LT bit in CR0 is 1, jumps from the current address to IAR + iX

Otherwise, does nothing

bge Branch if Greater than or Equal iX₂₄ if (x >= y) goto LABEL If either the GT bit or EQ bit in CR0 is 1, jumps from the current address to IAR + iX

Otherwise, does nothing

ble Branch if Less than or Equal iX₂₄ if (x <= y) goto LABEL If either the LT bit or EQ bit in CR0 is 1, jumps from the current address to IAR + iX

Otherwise, does nothing

bng Branch if Not Greater than
bnl Branch if Not Less than
bso Branch if Summary Overflow ??? ??? ???
bns Branch if Not Summary overflow ??? ??? ???
bun Branch if UNordered ??? ??? ???
bnu Branch if Not Unordered ??? ??? ???
bctr Branch to CounT Register
bctrl Branch to CounT Register and Link
bdnz Branch if Decremented count register Not Zero
bdnzt Branch if Decremented count register Not Zero and if condition True
bdnzf Branch if Decremented count register Not Zero and if condition False
bdz Branch if Decremented count register Zero
cmp CoMPare cr#, 0, rA, rB
cmpw CoMPare Word rA, rB
cmpwi CoMPare Word Immediate rA, iX₁₆
cmplwi CoMPare Logical Word Immediate
cntlzw CouNT Leading Zeros Word
divw DIVide Word rA, rB, rC rA = rB / rC Divides the value of rB by rC and stores the result in rA. The remainder is lost.
eieio Enforce In-order Execution of I/O ??? ??? ???
eqv EQuiValent rA, rB, rC rA = rB == rC Compares if the values of rB and rC are equal and stores the result in rA (?)
extsb EXTend Sign Byte rA, rB rA = (int8_t)rB Fills the upper 24 bits of rB's value with the sign bit of the stored 8 bit value
extsh EXTend Sign Halfword rA, rB rA = (int16_t)rB Fills the upper 16 bits of rB's value with the sign bit of the stored 16 bit value
fmr Float Move Register fA, fB fA = fB Copies the value of fB into fA (Despite the instruction name, fB is preserved)
isync Instruction SYNChronize N/A Assembly-only instruction Delay all following instructions until all previous instructions required for context.
lfs Load Float Single fA, iX₁₆(rA) fA = (float)(*(rA + iX)) Loads the value at the address (rA + iX) casted to float into fA.
lfd Load Float Double fA, iX₁₆(rA) fA = (double)(*(rA + iX)) Loads the 64 bit value at the address (rA + iX) casted to double into fA.
lbz Load Byte Zero-fill rA, iX₁₆(rB) rA = (ubyte)(*(rB + iX)) Loads the 8 bit value at the address (rB + iX) into rA
lhz Load Halfword Zero-fill rA, iX₁₆(rB) rA = (ushort)(*(rB + iX)) Loads the 16 bit value at the address (rB + iX) into rA
li Load Immediate rA, iX₁₆ rA = iX Loads iX into rA
lis Load Immediate Shifted rA, iX₁₆ rA = rA | (iX << 16) Loads iX into the upper 16 bits of rA
lwz Load Word Zero-fill rA, iX₁₆(rB) rA = *(rB + iX) Loads the value at the address (rB + iX) into rA
la Load Address rA, iX₁₆(rB) rA = rB + iX Adds iX to the address stored in rB and loads the result into rA.
lwzu Load Word Zero Update rA, iX₁₆(rB)
rA = *(rB + iX);
rB = rB + iX;
Loads the value at the address (rB + iX) into rA
Then loads rB with the address (rB + iX)
lwzx Load Word Zero indeXed rA, rB, rC rA = *(rB + rC) Loads the value at the address (rB + rC) into rA
lmw * Load Multiple Words rA, iX₁₆(rB)
int EA = rB + iX;
int N = rA;
do {
    GPR[N] = *(EA);
    EA = EA + 4;
    N = N + 1;
} while (N <= 31);
Loads GPR[rA] to r31 with the value at the address (rB + iX + N),

where N starts at 0 and increments by 4 for each register loaded.


Example: Assume r0 = 29 and r1 = 0x20000000
lmw r0, 0x20(r1)
This will load the following registers like so:
r29 = *(0x20000020)
r30 = *(0x20000024)
r31 = *(0x20000028)

mr Move Register rA, rB rA = rB Copies the value of rB into rA (Despite the instruction name, rB is preserved)
mflr Move From Link Register rA rA = LR Copies the value of LR into rA
mtlr Move To Link Register rA LR = rA Copies the value of rA into the LR
mtctr Move To CounT Register rA CTR = rA Copies the value of rA into the CTR
mtspr Move To Special Purpose Register SPR, rA SPRs[SPR] = rA Copies the value of rA into the special purpose register SPR
mtfsf * Move To FpScr Fields UNK1, fA ??? Copies the value of fA into the FPSCR under the control of the field mask in UNK1
mtfsb1 Move To FpScr Bit 1 iX? FPSCR = FPSCR | 0b1 << iX - 1 Sets bit iX of the FPSCR register to 1
mullw MULtiply Low Word rA, rB, rC rA = (int64_t)(rB * rC) & 0xFFFFFFFF Multiplies the value of rB by rC and stores the low 32 bits of the result in rA
mullh MULtiply (L) High word rA, rB, rC rA = (int64_t)(rB * rC) >> 32 Multiplies the value of rB by rC and stores the high 32 bits of the result in rA
mulli MULtiply Low Immediate rA, rB, iX₁₆ rA = rB * iX Multiplies the value of rB by iX and stores the result in rA
nand NAND operation rA, rB, rC rA = ~(rB & rC) Stores in rA the negated result of (rB & rC)
neg NEGate rA, rB rA = ~rB + 1 Stores in rA the result of negated rB with 1 added to it's value afterwards
nop No OPeration N/A ; Does nothing
nor NOR operation rA, rB, rC rA = ~(rB | rC) Stores in rA the negated result of (rB | rC)
not NOT operation rA, rB rA = ~rB Stores in rA the result of negated rB
or OR operation rA, rB, rC rA = rB | rC Stores in rA the result of (rB | rC)
orc OR Complement rA, rB, rC rA = rB | ~rC Stores in rA the result of (rB | ~rC)
ori OR Immediate rA, rB, iX₁₆ rA = rB | iX Stores in rA the result of (rB | iX)
oris OR Immediate Shifted rA, rB, iX₁₆ rA = rB | (iX << 16) Stores in rA the result of (rB | (iX << 16))
rlwinm Rotate Left Word Immediate aNd Mask rA, rB, iX₅, iY₅, iZ₅
uint mask = ((uint)-1) << (31 - iZ + iY) >> iY;
rA = (rB << iX) | (rB >> (32 - iX)) & mask;
Rotates the value in rB by iX bits to the left

The result of the above is AND'ed with the mask specified by iY and iZ

iY specifies the starting bit of the 1-bits in the mask (0-indexed)

iZ specifies the end bit of the 1-bits in the mask (0-indexed)

The final result is stored in rA

sc System Call iX₇ N/A Calls upon the system to perform a service identified by iX
slw Shift Left Word rA, rB, rC rA = rB << rC Shifts the value in rB by the value in rC to the left and stores the result in rA
slwi Shift Left Word Immediate rA, rB, iX₅ rA = rB << iX Shifts the value in rB by iX to the left and stores the result in rA
srw Shift Right Word rA, rB, rC rA = (unsigned)rB >> rC Shifts the value in rB by the value in rC to the right and stores the result in rA
srwi Shift Right Word Immediate rA, rB, iX₅ rA = (unsigned)rB >> iX Shifts the value in rB by iX to the right and stores the result in rA
sraw Shift Right Algebraic Word rA, rB, rC rA = (signed)rB >> rC Shifts the value in rB by the value in rC to the right and stores the result in rA

Unlike regular zero-fill right shift operations, this one sign-fills the vacant bits

srawi Shift Right Algebraic Word Immediate rA, rB, iX₅ rA = (signed)rB >> iX Shifts the value in rB by iX to the right and stores the result in rA

Unlike regular zero-fill right shift operations, this one sign-fills the vacant bits

subf SUBtract From rA, rB, rC rA = rC - rB Subtracts the value of rB from rC and stores the result in rA.
subfic SUBtract From Immediate Carrying rA, rB, iX₅ rA = iX - rB Subtracts the value of iX from rC and stores the result in rA. (CRO is modified)
stfs STore Float Single fA, iX₁₆(rA) *(rA + iX) = (float)fA Stores the value of fA casted to float at the memory address (rA + iX)
stfd STore Float Double fA, iX₁₆(rA) *(rA + iX) = fA Stores the 64 bit value of fA at the memory address (rA + iX)
stb STore Byte rA, iX₁₆(rB) *(rB + iX) = (ubyte)rA Stores the 8 bit value of rA at the memory address (rB + iX)
sth STore Halfword rA, iX₁₆(rB) *(rB + iX) = (ushort)rA Stores the 16 bit value of rA at the memory address (rB + iX)
stw STore Word rA, iX₁₆(rB) *(rB + iX) = rA Stores the value of rA at the memory address (rB + iX)
stwu STore Word And Update rA, iX₁₆(rB) *(rB + iX) = rA

rB = rB + iX

Stores the value of rA at the memory address (rB + iX)

Stores the computed address (rB + iX) into rB

stwx STore Word indeXed rA, rB, rC *(rB + rC) = rA Stores the value of rA at the memory address (rB + rC)
stmw * STore Multiple Words
xor XOR operation rA, rB, rC rA = rB ^ rC Performs an XOR operation on rB and rC then stores the result in rA
xori XOR Immediate rA, rB, iX₁₆ rA = rB ^ iX Performs an XOR operation on rB and iX then stores the result in rA
xoris XOR Immediate Shifted rA, rB, iX₁₆ rA = rB ^ (iX << 16) Performs an XOR operation on rB and (iX << 16) then stores the result in rA

External Resources