Add a readme

README.md

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+# `xchg rax, rax`
+
+So I got myself a hard copy of [`xchg rax, rax`](https://www.xorpd.net/pages/xchg_rax/snip_00.html).
+Now I have to learn enough `x86_64` assembler to read it.
+And probably also some `gdb` or `lldb` to inspect the running program.
+
+I'll try to do that.
+
+## Build
+
+Individual chapters are in their respective `0x??.asm` files, probably with added comments.
+They can be build using `make`:
+
+```
+make 0x00
+```
+
+Resulting in a binary file `0x00`
+
+## Debug
+
+Break on main, inspect the registers, run the full thing and inspect it again.
+
+```
+gdb 0x00
+(gdb) break main
+(gdb) run
+(gdb) info registers
+rax            0x401110            4198672
+rbx            0x7fffffffc968      140737488341352
+rcx            0x403e00            4210176
+rdx            0x7fffffffc978      140737488341368
+rsi            0x7fffffffc968      140737488341352
+rdi            0x1                 1
+rbp            0x1                 0x1
+-- snip --
+(gdb) continue
+```
+
+| Command | Short | Meaning |
+| ------- | ----- | ------- |
+| break main | b main | Set a breakpoint on the entry of function `main` |
+| run | r | Run the program until a breakpoint or end |
+| info registers | i r | Show values of all registers |
+| continue | c | Continue running the program |

template.asm

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 	global main
 
 main:
-	xor eax, eax