Put unused syscalls behind features

CounterClient and CryptoClient::attest are not currently used by the
solo2 or nk3 firmwares, but due to the indirect dispatch of Trussed
requests, they cannot be optimized out by the linker.  This patch
introduces feature flags for these syscalls that are enabled by default.

CHANGELOG.md

@@ -39,6 +39,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Made `postcard_deserialize`, `postcard_serialize` and
   `postcard_serialize_bytes` private.
 - Changed `&PathBuf` to `&Path` where possible.
+- Put `CounterClient` and `CryptoClient::attest` behind feature flags (enabled
+  by default).
 
 ### Fixed
 

Cargo.toml

@@ -60,7 +60,7 @@ serde_cbor = { feature = "0.11.2", features = ["std"] }
 # rand_core = { version = "0.5", features = ["getrandom"] }
 
 [features]
-default = ["default-mechanisms", "clients-5"]
+default = ["default-mechanisms", "default-syscalls", "clients-5"]
 serde-extensions = []
 std = []
 verbose-tests = ["littlefs2/ll-assertions"]
@@ -75,7 +75,6 @@ log-warn = []
 log-error = []
 
 # mechanisms
-# default-mechanisms = ["aes256-cbc", "chacha8-poly1305", "ed255", "hmac-sha256", "p256", "sha256", "trng"]
 default-mechanisms = [
     "aes256-cbc",
     "chacha8-poly1305",
@@ -107,6 +106,11 @@ tdes = ["des"]
 totp = ["sha-1"]
 trng = ["sha-1"]
 
+# syscalls
+default-syscalls = ["counter-client", "crypto-client-attest"]
+counter-client = []
+crypto-client-attest = []
+
 clients-1 = []
 clients-2 = []
 clients-3 = []

src/client.rs

@@ -305,6 +305,7 @@ pub trait CryptoClient: PollClient {
         })
     }
 
+    #[cfg(feature = "crypto-client-attest")]
     fn attest(
         &mut self,
         signing_mechanism: Mechanism,
@@ -568,13 +569,15 @@ pub trait CryptoClient: PollClient {
 
 /// Create counters, increment existing counters.
 pub trait CounterClient: PollClient {
+    #[cfg(feature = "counter-client")]
     fn create_counter(
         &mut self,
         location: Location,
     ) -> ClientResult<'_, reply::CreateCounter, Self> {
         self.request(request::CreateCounter { location })
     }
 
+    #[cfg(feature = "counter-client")]
     fn increment_counter(
         &mut self,
         id: CounterId,

src/service.rs

@@ -150,6 +150,7 @@ impl<P: Platform> ServiceResources<P> {
 
         let keystore = once(|this, ctx| this.keystore(ctx.path.clone()));
         let certstore = once(|this, ctx| this.certstore(ctx));
+        #[cfg(feature = "counter-client")]
         let counterstore = once(|this, ctx| this.counterstore(ctx));
 
         let filestore = &mut self.filestore(ctx.path.clone());
@@ -170,6 +171,7 @@ impl<P: Platform> ServiceResources<P> {
                 }.map(Reply::Agree)
             },
 
+            #[cfg(feature = "crypto-client-attest")]
             Request::Attest(request) => {
                 let mut attn_keystore: ClientKeystore<P::S> = ClientKeystore::new(
                     PathBuf::from("attn"),
@@ -179,6 +181,9 @@ impl<P: Platform> ServiceResources<P> {
                 attest::try_attest(&mut attn_keystore, &mut certstore(self, ctx)?, &mut keystore(self, ctx)?, request).map(Reply::Attest)
             }
 
+            #[cfg(not(feature = "crypto-client-attest"))]
+            Request::Attest(_) => Err(Error::RequestNotAvailable),
+
             Request::Decrypt(request) => {
                 match request.mechanism {
 
@@ -609,16 +614,24 @@ impl<P: Platform> ServiceResources<P> {
                 Ok(Reply::SetCustomStatus(reply::SetCustomStatus {}))
             }
 
+            #[cfg(feature = "counter-client")]
             Request::CreateCounter(request) => {
                 counterstore(self, ctx)?.create(request.location)
                     .map(|id| Reply::CreateCounter(reply::CreateCounter { id } ))
             }
 
+            #[cfg(not(feature = "counter-client"))]
+            Request::CreateCounter(_) => Err(Error::RequestNotAvailable),
+
+            #[cfg(feature = "counter-client")]
             Request::IncrementCounter(request) => {
                 counterstore(self, ctx)?.increment(request.id)
                     .map(|counter| Reply::IncrementCounter(reply::IncrementCounter { counter } ))
             }
 
+            #[cfg(not(feature = "counter-client"))]
+            Request::IncrementCounter(_) => Err(Error::RequestNotAvailable),
+
             Request::DeleteCertificate(request) => {
                  certstore(self, ctx)?.delete_certificate(request.id)
                     .map(|_| Reply::DeleteCertificate(reply::DeleteCertificate {} ))

tests/counter.rs

@@ -1,4 +1,5 @@
 #![cfg(feature = "virt")]
+#![cfg(feature = "counter-client")]
 
 mod client;
 mod store;