The PowerPC 600 series, part 10: Passing parameters, function prologues and epilogues

Raymond Chen August 17, 2018 Aug 17, 2018 08/17/18

We saw a little bit of the Windows NT software convention with our introduction to the table of contents. Today we'll start looking at the conventions related to the stack. (Believe it or not, this will connect back to the table of contents, but it'll take a while before we get there.) The format of the stack is as follows: That's a big ...

The PowerPC 600 series, part 9: The table of contents

Raymond Chen August 16, 2018 Aug 16, 2018 08/16/18

We saw that the PowerPC 600 series gives you absolute addressing to the top and bottom 32KB of address space. But that doesn't buy you much on Windows NT programs, because all of those addresses are not usable by 32-bit programs. By convention, the r2 register contains a value called the table of contents, which is a pointer to a list of ...

The PowerPC 600 series, part 8: Control transfer

Raymond Chen August 15, 2018 Aug 15, 2018 08/15/18

The PowerPC 600 series has a few types of control transfer instructions. Let's look at direct branches first. The direct branch instructions perform an unconditional relative branch to the target. It has a reach of ±32MB. All the "... and link" instructions set the lr register to the return address (the instruction after the branch). ...

The PowerPC 600 series, part 7: Atomic memory access and cache coherency

Raymond Chen August 14, 2018 Aug 14, 2018 08/14/18

On the PowerPC 600 series, memory accesses to suitably-aligned locations by a single register are atomic,¹ meaning that even in the face of a conflicting operation on another processor, the result will be the entire previous value or the entire final value, never a mix of the two. To perform atomic update operations (load-modify-store, ...

The PowerPC 600 series, part 6: Memory access

Raymond Chen August 13, 2018 Aug 13, 2018 08/13/18

The PowerPC 600 series has two addressing modes. We will demonstrate them with the lwz instruction, which loads a word from memory. The regular load instruction fetches a word from a memory location specified by a register and a signed 16-bit displacement. By convention, if no displacement is given, it is assumed to be zero. The Windows ...

The PowerPC 600 series, part 5: Rotates and shifts

Raymond Chen August 10, 2018 Aug 10, 2018 08/10/18

The Swiss army knife instruction of the PowerPC 600 series instruction set is rlwinm, which stands for "rotate left word immediate and mask." This instruction does everything except wash your floor. First it takes the current value of the ra register and rotates it left by imm5a bits. Then it keeps all the bits imm5b to imm5c, inclusive, and...

The PowerPC 600 series, part 4: Bitwise operations and constants

Raymond Chen August 9, 2018 Aug 9, 2018 08/9/18

The PowerPC 600 series includes the following bitwise logical operations: Each of these instructions also comes with a dot variant that updates cr0 based on the result. There are also versions that take immediates or sometimes shifted immediates, and sometimes they update flags, and sometimes they don't. There isn't much orthogonality here. ...

The PowerPC 600 series, part 3: Arithmetic

Raymond Chen August 8, 2018 Aug 8, 2018 08/8/18

Before we start with arithmetic, we need to have a talk about carry. The PowerPC uses true carry for both addition and subtraction. This is different from the x86 family of processors, for which the carry flag is actually a borrow bit when used in subtraction. You can read more about the difference on Wikipedia. There are some instructions ...

The PowerPC 600 series, part 2: Condition registers and the integer exception register

Raymond Chen August 7, 2018 Aug 7, 2018 08/7/18

The integer exception register xer contains a bunch of stuff, but the ones that are relevant to us are Some instructions update the overflow and summary overflow bits in the xer register. When those instructions are executed, the overflow bit is updated to represent whether the operation resulted in a signed overflow. The summary overflow ...

The PowerPC 600 series, part 1: Introduction

Raymond Chen August 6, 2018 Aug 6, 2018 08/6/18

The PowerPC is a RISC processor architecture which grew out of IBM's POWER architecture. Windows NT support was introduced in Windows NT 3.51, and it didn't last long; the last version to support it was Windows NT 4.0. Despite not being supported by the flagship operating system, it continued to be supported by Windows CE, and a later version ...