Chapter 1 notes/room for improvement

[Oakchris1955]

I spent some time today completing chapter 1 and I gathered the following notes:

1.1. Making a Stand Alone Binary

• Better to specify target in .cargo/config.toml in the following matter:

[build]
target = "x86_64-unknown-none"

1.2. Booting Our Binary

• json-target-spec = true must be added under [unstable] in .cargo/config.toml
• Rust doesn't like JSON comments, they should be removed from 16bit_target.json
• hexdump should be run on target/16bit_target/release/<project_name>. I believe it would be useful for the reader to know which file to run hexdump to. The binary path can also be obtained by running cargo build --release --message-format=json. There last JSON output should contain an executable field with the binary path.
• Better to test qemu-system-x86_64 by running it with the --version flag
  Not sure about that one, since we need to run it to compare before and after passing our binary. Do what you think is best.
• About the QEMU command: Perhaps it should be specified that the \ is
  to allow multiple lines (or it could also be removed)? Just saying because I got a bit confused about it.
• &ch: u8 in msg is incorrect syntax; has been fixed in the repo, not in the book
• Instead of passing --target, we can just set .cargo/config.toml build.target to 16bit_target.json
• The hlt command doesn't actually halt the system: it halts it until an interrupt
  is fired. I don't know if it is just me, but even with hlt, QEMU still uses 100% of one
  of my cores, because apparently it is checking for interrupts the entire time
  (source)
  but when I invoke the cli instruction (CLear Interrupt flag) before hlt, the CPU usage drops to almost zero.