Chapter 8, Addressing Modes

• Today's code words.asm
  • This relies on MY_IO.asm
  • Which I may have broken.
• Chapter 8 is mostly review.
• Intel assembly supports three addressing modes
  • registers, simply give the register name and the contents will be accessed/changed
  • immediate, the source for some operations, does not work everywhere.
  • Memory
    • if the name is used, this is simply an address
    • Inside [], this accesses memory
• Sometimes the assembler doesn't know the size of the instruction to use
  • inc [rbx]
  • In this case we might need to "cast".
  • inc byte [rbx]
  • The choices are
    • byte
    • word 16 bits, 2 bytes
    • dword, 32 bits, 4 bytes
    • qword, 64 bits, 8 bytes
• Null terminated strings
  • label resb 'string',0
  • Better for gdb.
  • x /10s &label
• More gdb
  • b functionname
  • s step to next instruction, into functions
  • n go to next instruction, skip function calls
• Array addressing
  • base address + index * elementSize
  • For strings, the element size is 1 byte.
• More conditional control, Jorgensen P 113 (7.7.3)
  • cmp will compare two values and set flags.
  • je, jne, jump equal, jump not equal
  • jl, jle, jg, jge, jump on condition for signed values
  • jb, jbe, ja, jae for unsigned (jump below, jump above)
  • See page 114.
  • We will be back for this soon.