From 359a92f770e621828e628f319290bb5736b1f67b Mon Sep 17 00:00:00 2001
From: Akshay <nerdypepper@tuta.io>
Date: Sun, 9 Feb 2020 10:24:03 +0530
Subject: new styles, new post!

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+My 4th semester involves ARM programming. And proprietary
+tooling (Keil C). But we don't do that here.
+
+### Building
+
+Assembling and linking ARM binaries on non-ARM architecture
+devices is fairly trivial. I went along with the GNU cross
+bare metal toolchain binutils, which provides `arm-as` and
+`arm-ld` (among a bunch of other utils that I don't care
+about for now). 
+
+Assemble `.s` files with:
+
+```shell
+arm-none-eabi-as main.s -g -march=armv8.1-a -o main.out
+```
+
+The `-g` flag generates extra debugging information that
+`gdb` picks up. The `-march` option establishes target
+architecture.
+
+Link `.o` files with:
+
+```shell
+arm-none-eabi-ld main.out -o main
+```
+
+### Running (and Debugging)
+
+Things get interesting here. `gdb` on your x86 machine
+cannot read nor execute binaries compiled for ARM. So, we
+simulate an ARM processor using `qemu`. Now qemu allows you
+to run `gdbserver` on startup. Connecting our local `gdb`
+instance to `gdbserver` gives us a view into the program's
+execution. Easy!
+
+Run `qemu`, with `gdbserver` on port `1234`, with our ARM
+binary, `main`:
+
+```shell
+qemu-arm -singlestep -g 1234 main
+```
+
+Start up `gdb` on your machine, and connect to `qemu`'s
+`gdbserver`:
+
+```
+(gdb) set architecture armv8-a
+(gdb) target remote localhost:1234
+(gdb) file main
+Reading symbols from main...  # yay!
+```
+
+### GDB Enhanced
+
+`gdb` is cool, but it's not nearly as comfortable as well
+fleshed out emulators/IDEs like Keil. Watching registers,
+CPSR and memory chunks update *is* pretty fun. 
+
+I came across `gdb`'s TUI mode (hit `C-x C-a` or type `tui
+enable` at the prompt). TUI mode is a godsend. It highlights
+the current line of execution, shows you disassembly
+outputs, updated registers, active breakpoints and more.
+
+*But*, it is an absolute eyesore.
+
+Say hello to [GEF](https://github.com/hugsy/gef)! "GDB
+Enhanced Features" teaches our old dog some cool new tricks.
+Here are some additions that made my ARM debugging
+experience loads better:
+
+ - Memory watches
+ - Register watches, with up to 7 levels of deref (overkill,
+   I agree)
+ - Stack tracing
+
+And its pretty! See for yourself:
+
+![gef.png](https://u.peppe.rs/wq.png)
+
+### Editing
+
+Vim, with `syntax off` because it
+dosen't handle GNU ARM syntax too well.
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