Use Tock's QEMU instead of our own QEMU.

I also switched to using `cargo clean` in the Makefile rather than manually removing `target/` and `Cargo.lock`, as that seems like a more correct and maintainable design.

.gitignore

diff --git a/.gitignore b/.gitignore
index 798463e..ae858ab 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,3 @@
-/build
 /Cargo.lock
 /layout.ld
 /platform

Cargo.toml

diff --git a/Cargo.toml b/Cargo.toml
index ee68117..0016e7a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -58,6 +58,7 @@
 debug = true
 
 [workspace]
+exclude = [ "tock" ]
 members = [
     "codegen",
     "core",

Makefile

diff --git a/Makefile b/Makefile
index ae326fb..cf1a305 100644
--- a/Makefile
+++ b/Makefile
@@ -41,18 +41,11 @@
 	cargo install elf2tab --version 0.4.0
 	cargo install stack-sizes
 
-# Downloads a version of QEMU with patches needed to support Tock on HiFive.
-# Builds QEMU and installs it into build/.
+# Sets up QEMU in the tock/ directory. We use Tock's QEMU which may contain
+# patches to better support boards that Tock supports.
 .PHONY: setup-qemu
 setup-qemu:
-	mkdir -p build
-	cd build                                              && \
-	git clone https://github.com/alistair23/qemu.git         \
-	          -b riscv-tock.next --depth 1                && \
-	cd qemu                                               && \
-	./configure --prefix=$(CURDIR)/build                     \
-	            --target-list=arm-softmmu,riscv32-softmmu && \
-	$(MAKE) install
+	$(MAKE) -C tock emulation-setup
 
 # Builds a Tock kernel for the HiFive board for use by QEMU tests.
 .PHONY: kernel-hifive
@@ -62,7 +55,7 @@
 
 # Runs the libtock_test tests in QEMU on a simulated HiFive board.
 .PHONY: test-qemu-hifive
-test-qemu-hifive: kernel-hifive
+test-qemu-hifive: kernel-hifive setup-qemu
 	PLATFORM=hifive1 cargo rrv32imac --example libtock_test --features=alloc \
 		--features=__internal_disable_gpio_in_integration_test
 	cargo run -p test-runner
@@ -136,5 +129,5 @@
 
 .PHONY: clean
 clean:
-	rm -rf target
-	rm Cargo.lock
+	cargo clean
+	$(MAKE) -C tock clean

test-runner/src/main.rs

diff --git a/test-runner/src/main.rs b/test-runner/src/main.rs
index b08d97b..e297e8e 100644
--- a/test-runner/src/main.rs
+++ b/test-runner/src/main.rs
@@ -14,7 +14,7 @@
 async fn perform_tests() -> Result<(), Box<dyn std::error::Error>> {
     let mut failed_tests = Vec::new();
 
-    let  tests = Command::new("build/bin/qemu-system-riscv32")
+    let tests = Command::new("tock/tools/qemu/riscv32-softmmu/qemu-system-riscv32")
         .arg("-M")
         .arg("sifive_e,revb=true")
         .arg("-kernel")