Document x86 assembly examples

x86-assembly/src/exit/exit.s

@@ -3,10 +3,14 @@
 
 _start:
 	# Store system call 1 in the EAX register.
+	# mov = instruction
+	# $1, %eax = operands
+	# %eax = register
 	mov $1, %eax
 
 	# Store the exit code 0 in the EBX register.
 	mov $0, %ebx
 
 	# Call interrupt handler 0x80 (128) -- on Linux, this is the kernel.
+	# Kernel will take over and see 1 in %eax, 0 in %ebx.
 	int $0x80

x86-assembly/src/func/func.s

@@ -14,18 +14,28 @@ _start:
 # square expects an integer on the stack, 16 bytes down from RBP.
 # The squared value is returned on %rax.
 square:
-	# Function Epilogue --> {
+	# Function Prologue --> {
 	push %rbp
         mov %rsp, %rbp
 
 	# Retrieve the parameter from the stack.
 	# 8 bytes down from RSP is the return address from square.
-	# 8 bytes down from that is the parameter to multiple.
+	# 8 bytes down from that is the parameter to multiply.
 	mov 16(%rbp), %rax
 	mul %rax
 
-	# Function Prologue --> }
+	# Function Epilogue --> }
 	mov %rbp, %rsp
         pop %rbp
-	# ret pops and return to address on stack.
+	# ret pops and returns to address on stack.
 	ret
+
+# |----------------+-----------+----------------|
+# |        Address |      Data | Stack Pointers |
+# |----------------+-----------+----------------|
+# | 0x7fffffffe8f8 |           |                |
+# | 0x7fffffffe900 | 0x0 (rbp) |                |
+# | 0x7fffffffe908 |  0x401002 |                |
+# | 0x7fffffffe910 |         3 | ←rsp           |
+# |----------------+-----------+----------------|
+#  ←rbp