flipperzero: Enable Miri to start running the tests

It doesn't *successfully* run the tests because Miri doesn't yet support
FFI, but these changes enable the following command to actually start:

    MIRI_NO_STD=1 cargo miri test --target thumbv7em-none-eabihf

Part of #100.

crates/.cargo/config.toml

@@ -1,6 +1,10 @@
+# Equivalent to [target.thumbv7em-none-eabihf] but also disabing the runner for Miri.
+# Until target_abi is stable, this also permits thumbv7em-none-eabi.
+[target.'cfg(all(target_arch = "arm", target_feature = "thumb2", target_feature = "v7", target_feature = "dsp", target_os = "none", not(miri)))']
+runner = "python3 ../cargo-runner.py"
+
 [target.thumbv7em-none-eabihf]
 linker = "./fap-lld.py"
-runner = "python3 ../cargo-runner.py"
 rustflags = [
     # CPU is Cortex-M4 (STM32WB55)
     "-C", "target-cpu=cortex-m4",

crates/flipperzero/src/lib.rs

@@ -5,7 +5,8 @@
 //!
 
 #![no_std]
-#![cfg_attr(test, no_main)]
+#![cfg_attr(all(test, not(miri)), no_main)]
+#![cfg_attr(all(test, miri), feature(start))]
 #![cfg_attr(docsrs, feature(doc_cfg))]
 #![deny(rustdoc::broken_intra_doc_links)]
 

crates/rt/src/lib.rs

@@ -34,6 +34,7 @@ macro_rules! entry {
     ($path:path) => {
         // Force the section to `.text` instead of `.text.main`.
         // lld seems not to automatically rename `.rel.text.main` properly.
+        #[cfg(not(miri))]
         #[export_name = "main"]
         pub unsafe fn __main(args: *mut u8) -> i32 {
             // type check the entry function

crates/sys/src/lib.rs

@@ -5,13 +5,16 @@
 
 // Features that identify thumbv7em-none-eabihf.
 // Until target_abi is stable, this also permits thumbv7em-none-eabi.
-#[cfg(not(all(
-    target_arch = "arm",
-    target_feature = "thumb2",
-    target_feature = "v7",
-    target_feature = "dsp",
-    target_os = "none",
-    //target_abi = "eabihf",
+#[cfg(not(any(
+    all(
+        target_arch = "arm",
+        target_feature = "thumb2",
+        target_feature = "v7",
+        target_feature = "dsp",
+        target_os = "none",
+        //target_abi = "eabihf",
+    ),
+    miri
 )))]
 core::compile_error!("This crate requires `--target thumbv7em-none-eabihf`");
 

crates/test/macros/src/lib.rs

@@ -131,14 +131,27 @@ fn tests_runner_impl(args: TokenStream) -> parse::Result<TokenStream> {
             }
 
             // Test runner entry point
-            fn main(args: Option<&::core::ffi::CStr>) -> i32 {
+            pub(super) fn main(args: Option<&::core::ffi::CStr>) -> i32 {
                 let args = ::flipperzero_test::__macro_support::Args::parse(args);
                 match ::flipperzero_test::__macro_support::run_tests(test_count(), test_list(), args) {
                     Ok(()) => 0,
                     Err(e) => e,
                 }
             }
         }
+
+        #[cfg(all(test, miri))]
+        #[start]
+        fn main(argc: isize, argv: *const *const u8) -> isize {
+            // TODO: Is there any benefit to Miri in hooking up the binary arguments to
+            // the test runner?
+            let ret = __test_runner::main(None);
+
+            // Clean up app state.
+            ::flipperzero_rt::__macro_support::__wait_for_thread_completion();
+
+            ret.try_into().unwrap_or(isize::MAX)
+        }
     )
     .into())
 }