memory added

x86_64/2_memory.asm

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+global _start
+
+section .data
+  str: db '0123456789',0xA
+  strSize: equ $ - str
+  stdout: equ 1
+
+section .text
+_start:
+  ; Print the string
+  mov rdx, strSize
+  mov rsi, str
+  mov rdi, stdout
+  mov rax, 1
+  syscall
+
+  ; mov byte [rsi], 3 == *rsi = 3
+  ; Move the value of 3 into the address contained in register RSI
+  ; Note the type specifier
+  ; byte, word, dword
+
+  ; The official syntax is
+  ;mov byte ptr [rsi], 3
+  ; But the ptr is implicitly meant with the []'s, so nasm allows
+  ; us to leave it out
+
+
+  mov byte [rsi], 'a'
+  mov rax, 1
+  syscall
+
+  mov word [rsi], 'bc'
+  mov rax, 1
+  syscall
+
+  mov dword [rsi], 'defg'
+  mov rax, 1
+  syscall
+
+  ; "In 64-bit mode, a memory operand can be referenced by
+	; a segment selector and an offset. [...]
+	; The offset part of a memory address in 64-bit mode can be
+	; specified directly as a static value or through an address
+	; computation made up of one or more of the following components:
+	;	Displacement -- An 8-bit, 16-bit, or 32-bit value.
+	;	Base -- The value in a 64-bit general-purpose register.
+	;	Index -- The value in a 64-bit general-purpose register.
+	;	Scale factor -- A value of 2, 4, or 8 that is multiplied
+	;	by the index value."
+	; In intel syntax, this is written as:
+	;	[base + scale * index + displacement]
+  ; Example:
+  ; [rax + 2 * rbx + 0xdeadbeef]
+	; (most of these are optional; see below).
+
+  mov byte [rsi], 'h' ; base only
+  mov rax, 1
+  syscall
+
+  mov byte [str], 'i'   ; displacement only
+  mov byte [str+1], 'j' ; displacement only too (assembler evaluates it) 
+  mov rax, 1
+  syscall
+
+  mov rbx, 3
+  mov byte [rsi+2], 'k'
+  mov byte [rsi+rbx], 'l'
+  mov byte [rsi+2*rbx], 'm'
+  mov byte [rsi+2*rbx+2], 'n'
+  mov rax, 1
+  syscall
+
+  ; Load Effective Address
+  ; Calculate the address of the expression, it does NOT load the value!
+  mov rbx, 2
+  lea rsi, [str+2*rbx] ; = rsi = str + (2 * 2)
+
+  ; Due to this powerful feature it is often used with invalid
+  ; addresses: you can use it to do generic calculations!
+  mov rbx, -2
+  lea rdx, [strSize+2*rbx] ; print (strSize - 4) characters
+  mov rax, 1
+  syscall
+
+  ; Exit
+  mov rax, 60
+  xor rdi, rdi
+  syscall