Videos: Representing Control Flow

These videos about conditionals and jump instructions will especially prepare you for the second lab assignment, where you’ll have to infer the behavior of a program given only its machine code.

• Control 1: Condition codes   4:39
  Overview of x86-64 condition codes and how they’re set.

• Control 2: Interpreting condition codes   3:03
  Interpreting condition codes as number comparisons.

• Control 3: setcc, cmpx, and testx   4:46
  Instructions for using and setting condition codes.

• Control 4: Extended example for setcc   3:11
  Working backward from machine code with setcc instructions to a C source.

• Control 5: cmovccx   1:42
  The cmovcxx instruction. Although this instruction is used infrequently (for technical and historical reasons), it helps set up the idea of jumps.

• Control 6: Jumps via jcc and jmp   2:27
  Introduction to “jump” instructions to implement if branches.

• Control 7: Alternative branch patterns   1:39
  An note on implementation variants for if branches, which foreshadows implementation variants for loops.

• Control 8: Additional branch example   2:49
  Another concrete example of machine code that is generated for an if branch.

• Control 9: do–while loops   3:07
  Compiling do–while loops to jumps.

• Control 10: while loops   4:30
  Compiling while loops to jumps.

• Control 11: for loops   1:14
  Compiling for loops to jumps and why that’s essentially the same as compiling while loops.

• Control 12: Another loop exercise   2:52
  Given C code and machine code, figuring out how registers are used in the machine code to implement variables of the C code.

• Control 13: switch and jump tables   6:28
  The switch form in C and its implementation through conditions and jump tables—especially jump tables.

• Control 14: Compiler-generated jump tables   4:58
  Still more on jump tables, where the details are slightly different when generated by a compiler relative to the hand-rolled table of the previous video.