X86 64 Register and Instruction Quick Start

== Registers ==

General-Purpose Registers

The 64-bit versions of the 'original' x86 registers are named:

• rax - register a extended
• rbx - register b extended
• rcx - register c extended
• rdx - register d extended
• rbp - register base pointer (start of stack)
• rsp - register stack pointer (current location in stack, growing downwards)
• rsi - register source index (source for data copies)
• rdi - register destination index (destination for data copies)

The registers added for 64-bit mode are named:

• r8 - register 8
• r9 - register 9
• r10 - register 10
• r11 - register 11
• r12 - register 12
• r13 - register 13
• r14 - register 14
• r15 - register 15

These may be accessed as:

• 64-bit registers using the 'r' prefix: rax, r15
• 32-bit registers using the 'e' prefix (original registers: e_x) or 'd' suffix (added registers: r__d): eax, r15d
• 16-bit registers using no prefix (original registers: _x) or a 'd' suffix (added registers: r__d): ax, r15d
• 8-bit registers using 'h' suffix (original registers - bits 8-15: _h): ah, bh
• 8-bit registers using 'l' suffix (original registers - bits 0-7: _l) or 'b' suffix (added registers: r__b): al, bl, r15b

Usage during syscall/function call:

• First six arguments are in rdi, rsi, rdx, rcx, r8d, r9d; remaining arguments are on the stack
• For syscalls, the syscall number is in rax
• Return value is in rax
• The called routine is expected to save rsp,rbp, rbx, r12, r13, r14, and r15 but may trample any other registers

Instructions

Starter Kit

These instructions are sufficient to complete the SPO600 Assembler Lab:

add %r10,%r11                      // add r10 and r11, put result in r11
cmp %r10,%r11                      // compare register r10 with register r11
cmp $99,%r11                       // compare the number 99 with register r11
div $r10                           // divide rax by the given register (r10), places quotient into rax and remainder into rdx (rdx must be zero before this instruction)
inc %r10                           // increment r10
jmp label                          // jump to label
jeq label                          // jump to label if equal
jne label                          // jump to label if not equal
jl  label                          // jump to label if less
jg  label                          // jump to label if greater
mov %r10,%r11                      // move data from r10 to r11
mov $99,%r10                       // put the immediate value 99 into r10
mov %r10,(%r11)                    // move data from r10 to address pointed to by r11
mov (%r10),%r11                    // move data from address pointed to by r10 to r10
mul $r10                           // multiplies rax by r10, places result in rax and overflow in rdx
push %r10                          // push r10 onto the stack
pop %r10                           // pop r10 off the stack

References

• For full information on the x86_64 registers and instruction set, see the Intel manuals: http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html