Build ROM_EXT signer by default

Signed-off-by: Alphan Ulusoy <alphan@google.com>
diff --git a/ci/install-package-dependencies.sh b/ci/install-package-dependencies.sh
index a3cc3b7..b16378d 100755
--- a/ci/install-package-dependencies.sh
+++ b/ci/install-package-dependencies.sh
@@ -134,11 +134,12 @@
 sudo mkdir -p /tools/verible
 sudo chmod 777 /tools/verible
 tar -C /tools/verible -xf "$verible_tar" --strip-components=1
-
-# Propagate PATH changes to all subsequent steps of the job
-echo "##vso[task.setvariable variable=PATH]/tools/verible/bin:$PATH"
+export PATH=/tools/verible/bin:$PATH
 
 # Install Rust
 sw/vendor/rustup/rustup-init.sh -y \
     --default-toolchain "${RUST_VERSION}"
-export PATH="$HOME/.cargo/bin:$PATH"
+export PATH=$HOME/.cargo/bin:$PATH
+
+# Propagate PATH changes to all subsequent steps of the job
+echo "##vso[task.setvariable variable=PATH]$PATH"
diff --git a/doc/ug/install_instructions/index.md b/doc/ug/install_instructions/index.md
index 4497dae..e44c160 100644
--- a/doc/ug/install_instructions/index.md
+++ b/doc/ug/install_instructions/index.md
@@ -58,7 +58,7 @@
 * Cmake 2.8.11
 * Perl 5.6.1
 * [Go](https://golang.org/) 1.10
-* [Rust](https://www.rust-lang.org/) 1.52.1
+* [Rust](https://www.rust-lang.org/) {{< tool_version "rust" >}} (x86_64-unknown-linux-gnu)
 
 To synthesize and simulate the hardware components of OpenTitan multiple EDA tools are supported.
 Depending on how you interact with the OpenTitan hardware code, one of more of the following tools need to be available.
diff --git a/sw/host/rom_ext_image_tools/signer/meson.build b/sw/host/rom_ext_image_tools/signer/meson.build
index 0a00996..7bae63e 100644
--- a/sw/host/rom_ext_image_tools/signer/meson.build
+++ b/sw/host/rom_ext_image_tools/signer/meson.build
@@ -31,8 +31,8 @@
 # The cargo invocation script.
 cargo_invoke_cmd = meson.source_root() / 'util/invoke_cargo.sh'
 
-rom_ext_signer_raw = custom_target(
-  'rom_ext_signer_raw',
+rom_ext_signer = custom_target(
+  'rom_ext_signer',
   command: [
     cargo_invoke_cmd,
     cargo,
@@ -49,15 +49,14 @@
   output: '.',
   console: true,
   build_always_stale: true,
-  build_by_default: false,
+  build_by_default: true,
 )
 
-rom_ext_signer_elf = custom_target(
-  'rom_ext_signer_elf',
+rom_ext_signer_export = custom_target(
+  'rom_ext_signer_export',
   command: ['cp', '@INPUT@' / build_type / 'rom_ext_signer', '@OUTPUT@'],
-  depends: rom_ext_signer_raw,
-  input: rom_ext_signer_raw,
-  output: 'rom_ext_signer.elf',
+  input: rom_ext_signer,
+  output: 'rom_ext_signer',
   build_always_stale: true,
-  build_by_default: false,
+  build_by_default: true,
 )
diff --git a/tool_requirements.py b/tool_requirements.py
index 922ce5e..770b698 100644
--- a/tool_requirements.py
+++ b/tool_requirements.py
@@ -36,5 +36,9 @@
     'vcs': {
         'min_version': '2020.03-SP2',
         'as_needed': True
-    }
+    },
+    'rust': {
+        'min_version': '1.52.1',
+        'as_needed': True
+    },
 }