From f627ab2ec60b2b861a6adb22f7d66429439ef601 Mon Sep 17 00:00:00 2001
From: Tijmen van Nesselrooij <tijmen_222@hotmail.com>
Date: Sun, 10 Mar 2019 12:17:59 +0100
Subject: [PATCH] x86_64 added

---
 x86_64/0_basic.asm | 117 +++++++++++++++++++++++++++++++++++++++++++++
 x86_64/README.md   |  15 ++++++
 x86_64/debug.sh    |  22 +++++++++
 x86_64/makefile    |  21 ++++++++
 4 files changed, 175 insertions(+)
 create mode 100644 x86_64/0_basic.asm
 create mode 100644 x86_64/README.md
 create mode 100644 x86_64/debug.sh
 create mode 100644 x86_64/makefile

diff --git a/x86_64/0_basic.asm b/x86_64/0_basic.asm
new file mode 100644
index 0000000..b06ee22
--- /dev/null
+++ b/x86_64/0_basic.asm
@@ -0,0 +1,117 @@
+global _start
+
+; !! THIS IS INTEL STYLE ASSEMBLY !!
+
+section .data
+	; This is an array, db = declare bytes
+	my_arr: db 0x12,0x34,0x56,0x78,0x90
+
+	; Some basic types:
+	; byte = 8 bits
+	; word = 16 bits
+	; double word = dword = 32 bits
+	; quad word = qword = 64 bits
+
+	; To declare them:
+	; db
+	; dw
+	; dd
+	; dq
+
+	; Endianness examples, this will be stored in reverse
+	; e.g. 0xbeef -> 0xef 0xbe in memory
+	little_endian: dw 0xbeef
+
+	; Supplying not enough bytes means the remainder will be zero filled
+	zerod_remainder: dw 0x42 ; = 0x42 0x00 in memory
+
+	; Equ works like #define
+	; It does get a symbol however, and can thus be used by other
+	; assemblies (by making it global). This value gets inlined.
+	; Useful for constant expressions
+	PI: equ 3
+
+section .text
+
+; Entry point
+_start:
+	; Move 0 into the register RAX (64 bits)
+	mov rax, 0 
+
+	; General purpose registers (A, B, C, D, ...)
+	; rax = accumulator
+	; rbx = base
+	; rcx = counter
+	; rdx = destination
+	; rsp & rbp = stack pointer (sp) and base pointer(bp)
+	; rsi & rdi = source index (si) and destination index (di)
+	; r8 - r15  = plain old registers
+
+	; Note that for all registers except the r8-r15 speficic bits
+	; can be addressed by changing the prefix and postfix, e.g.
+	; for register A: rax, eax, ax, al and ah
+
+	mov eax, 0xdeadbeef ; Copy 32 bits, 4 bytes, 1 dword
+	mov ebx, 0xabcd ; = mov ebx, 0x0000abcd
+	mov cl, 0xFF
+	mov ch, 0x00
+	; ecx = 0x00FF
+
+	; Some basic arithmetic
+	mov rdi, 10
+	mov rsi, 7
+	mov rbx, 14
+
+	inc rdi ; increment
+	dec rsi ; decrement
+
+	; note: operator dest, src
+	add rdi, rbx ; stores the ADD result in the first operand (rdi)
+	sub rsi, rbx ; rsi = rsi - rbx
+
+	; By default all arithmetic assumes unsigned values. Prepend with I to
+	; use signed math (e.g. imul, idiv, etc.)
+
+	; Multiplication 
+	; Yields 128 bit values
+	; It multiplies the operand with the value of register A
+	; Stores the lower 64 bits in register A and the upper 64 bits in
+	; Register D
+	mov rax, 7
+	mov rdx, 4
+	mov rdi, 3
+	mul rdi ; rax = rax * rdi, rdx = 0 (because no overflow)
+
+	; Division
+	; Yields a 128 bit value 
+	; The result (64 bits) is stored in register A
+	; The remainder (64 bits) is stored in register D
+	mov rax, 22 ; divident, to be result
+	mov rdx, 0  ; to be remainder	
+	mov rdi, 5  ; divider
+
+	div rdi ; rax = 22/5 = 4, rdx = 2
+
+	; Bitwise operations
+	; AND
+	; OR
+	; XOR
+	; SHR
+	; SHL
+
+	mov rdi, 0x35
+	mov rsi, 0x44
+	
+	and rdi, rsi
+	or rdi, rsi
+	xor rdi, rsi
+
+	shr rsi, 2 ; rsi >> 2
+	shl rsi, 3 ; rsi << 3
+	
+	; There is also SAL and SAR for arithmetic left- and right shifts
+
+	mov rax, 60
+	xor rdi, rdi ; zero it
+	syscall
+
diff --git a/x86_64/README.md b/x86_64/README.md
new file mode 100644
index 0000000..d11f550
--- /dev/null
+++ b/x86_64/README.md
@@ -0,0 +1,15 @@
+# Build steps
+
+## Assembling
+Assembling with NASM
+```bash
+nasm -g -f elf64 <file.asm>
+```
+- g = include debug info
+- f = file format (elf64 -> x64)
+
+## Linking
+```bash
+ld <object-files> -o <executable-name>  # Default
+gcc <object-files> -o <executable-name> # When using C library functions
+```
diff --git a/x86_64/debug.sh b/x86_64/debug.sh
new file mode 100644
index 0000000..6f7176f
--- /dev/null
+++ b/x86_64/debug.sh
@@ -0,0 +1,22 @@
+#!/bin/bash
+
+if [ -z "$1" ]; then
+	echo "Provide the program to debug as first argument"
+	exit 1
+fi
+
+if [ ! -x "$1" ]; then
+	echo "$1 is not an executable file"
+	exit 1
+fi
+
+echo "I will launch gdbtui soon. Use \"break *<entry-address>\" to debug the program."
+echo "Use \"layout asm\" to use a more assembly friendly layout"
+echo "Use \"si\" to single step each instruction"
+echo ""
+
+echo "$(readelf -h $1 | egrep "Entry point")"
+read -p "Copy the above address and press any key to continue..."
+
+gdbtui -q $1
+
diff --git a/x86_64/makefile b/x86_64/makefile
new file mode 100644
index 0000000..7fde932
--- /dev/null
+++ b/x86_64/makefile
@@ -0,0 +1,21 @@
+CC = gcc
+AS = nasm
+LD = ld
+
+.PHONY: all clean
+
+all: build 0_basic
+
+clean:
+	-rm -r build
+	-rm 0_basic
+
+build:
+	mkdir build
+
+build/%.o: %.asm
+	$(AS) -g -f elf64 $< -o $@
+
+0_basic: build/0_basic.o
+	$(LD) $< -o $@
+