View source for X86 64 Register and Instruction Quick Start

[[Category:Assembler]]== 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