From ab696eca8ec4f84692bf74ab4418b9445418804f Mon Sep 17 00:00:00 2001
From: Berkus Decker <berkus+github@metta.systems>
Date: Tue, 27 Oct 2020 13:38:59 +0200
Subject: [PATCH] Implement Error type for traps module

Recommended by the clippy lint
https://rust-lang.github.io/rust-clippy/master/index.html#result_unit_err

Using snafu because it already has a no_std feature
unlike thiserror.
---
 Cargo.lock                        | 63 +++++++++++++++++++++++++++++++
 nucleus/Cargo.toml                |  1 +
 nucleus/src/arch/aarch64/traps.rs | 13 ++++++-
 3 files changed, 75 insertions(+), 2 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 2ead162..5418063 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -27,12 +27,36 @@ dependencies = [
  "register",
 ]
 
+[[package]]
+name = "doc-comment"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fea41bba32d969b513997752735605054bc0dfa92b4c56bf1189f2e174be7a10"
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e0704ee1a7e00d7bb417d0770ea303c1bccbabf0ef1667dae92b5967f5f8a71"
+dependencies = [
+ "unicode-xid",
+]
+
 [[package]]
 name = "qemu-exit"
 version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b73ae13954572c7ca0ec48ba9fe6a59c0392066eba62f8cb384ffd5addf538c5"
 
+[[package]]
+name = "quote"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa563d17ecb180e500da1cfd2b028310ac758de548efdd203e18f283af693f37"
+dependencies = [
+ "proc-macro2",
+]
+
 [[package]]
 name = "r0"
 version = "1.0.0"
@@ -54,12 +78,50 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fc874b127765f014d792f16763a81245ab80500e2ad921ed4ee9e82481ee08fe"
 
+[[package]]
+name = "snafu"
+version = "0.6.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9c4e6046e4691afe918fd1b603fd6e515bcda5388a1092a9edbada307d159f09"
+dependencies = [
+ "doc-comment",
+ "snafu-derive",
+]
+
+[[package]]
+name = "snafu-derive"
+version = "0.6.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7073448732a89f2f3e6581989106067f403d378faeafb4a50812eb814170d3e5"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "syn"
+version = "1.0.48"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cc371affeffc477f42a221a1e4297aedcea33d47d19b61455588bd9d8f6b19ac"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-xid",
+]
+
 [[package]]
 name = "tock-registers"
 version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "70323afdb8082186c0986da0e10f6e4ed103d681c921c00597e98d9806dac20f"
 
+[[package]]
+name = "unicode-xid"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7fe0bb3479651439c9112f72b6c505038574c9fbb575ed1bf3b797fa39dd564"
+
 [[package]]
 name = "usize_conversions"
 version = "0.2.0"
@@ -84,6 +146,7 @@ dependencies = [
  "r0",
  "register",
  "rlibc",
+ "snafu",
  "usize_conversions",
  "ux",
 ]
diff --git a/nucleus/Cargo.toml b/nucleus/Cargo.toml
index 76fc81d..8eca98b 100644
--- a/nucleus/Cargo.toml
+++ b/nucleus/Cargo.toml
@@ -31,3 +31,4 @@ bit_field = "0.10.0"
 register = "0.5.1"
 bitflags = "1.2.1"
 cfg-if = "1.0"
+snafu = { version = "0.6", default-features = false }
diff --git a/nucleus/src/arch/aarch64/traps.rs b/nucleus/src/arch/aarch64/traps.rs
index 8fc3986..86f7d33 100644
--- a/nucleus/src/arch/aarch64/traps.rs
+++ b/nucleus/src/arch/aarch64/traps.rs
@@ -55,19 +55,28 @@ use {
         barrier,
         regs::{RegisterReadOnly, RegisterReadWrite, ESR_EL1, FAR_EL1, VBAR_EL1},
     },
+    snafu::Snafu,
 };
 
 global_asm!(include_str!("vectors.S"));
 
+/// Errors possibly returned from the traps module.
+#[derive(Debug, Snafu)]
+pub enum Error {
+    /// IVT address is unaligned.
+    #[snafu(display("Unaligned base address for interrupt vector table"))]
+    Unaligned,
+}
+
 /// Configure base address of interrupt vectors table.
 /// Checks that address is properly 2KiB aligned.
 ///
 /// # Safety
 ///
 /// Totally unsafe in the land of the hardware.
-pub unsafe fn set_vbar_el1_checked(vec_base_addr: u64) -> Result<(), ()> {
+pub unsafe fn set_vbar_el1_checked(vec_base_addr: u64) -> Result<(), Error> {
     if vec_base_addr.trailing_zeros() < 11 {
-        return Err(());
+        return Err(Error::Unaligned);
     }
 
     VBAR_EL1.set(vec_base_addr);