Introduce current the read counters SBI call

The READ_COUNTERS SBI call returns the performance counters as recorded
by the benchmark module. The specific ABI and counters returns depend
on the benchmark module compiled with Miralis.


Co-authored-by: Charly Castes <charly.castes@epfl.ch>

Author: francois141

crates/core/src/lib.rs

@@ -24,6 +24,8 @@ pub mod abi {
     pub const MIRALIS_LOG_FID: usize = 2;
     /// Benchmark prints and exit.
     pub const MIRALIS_BENCHMARK_FID: usize = 3;
+    /// Returns the performance counters managed by Miralis.
+    pub const MIRALIS_READ_COUNTERS_FID: usize = 4;
 
     /// Log level constants, with the same semantic as the `log` crate.
     pub mod log {

src/benchmark/default.rs

@@ -4,10 +4,12 @@
 //! the number of instruction for example.
 use spin::Mutex;
 
-use crate::arch::{Arch, Architecture, Csr};
+use crate::arch::{Arch, Architecture, Csr, Register};
 use crate::benchmark::{BenchmarkModule, Counter, Scope};
 use crate::config;
 use crate::platform::{Plat, Platform};
+use crate::virt::traits::*;
+use crate::virt::VirtContext;
 
 #[macro_export]
 macro_rules! _benchmark_print {
@@ -180,6 +182,19 @@ impl BenchmarkModule for DefaultBenchmark {
         BENCH.lock().counters[index] += 1;
     }
 
+    fn read_counters(ctx: &mut VirtContext) {
+        let benchmark = BENCH.lock();
+
+        ctx.set(
+            Register::X10,
+            benchmark.counters[Counter::FirmwareExits as usize],
+        );
+        ctx.set(
+            Register::X11,
+            benchmark.counters[Counter::WorldSwitches as usize],
+        );
+    }
+
     /// Print formated string with value of the counters
     fn display_counters() {
         let bench = BENCH.lock();

src/benchmark/empty.rs

@@ -1,5 +1,6 @@
 use crate::benchmark::default::IntervalCounter;
 use crate::benchmark::{BenchmarkModule, Counter, Scope};
+use crate::virt::VirtContext;
 
 pub struct EmptyBenchmark {}
 
@@ -26,6 +27,8 @@ impl BenchmarkModule for EmptyBenchmark {
     ) {
     }
 
+    fn read_counters(_ctx: &mut VirtContext) {}
+
     fn display_counters() {}
 
     fn get_counter_value(_counter: Counter) -> usize {

src/benchmark/mod.rs

@@ -8,6 +8,7 @@ mod empty;
 use config_select::select_env;
 
 use crate::benchmark::default::IntervalCounter;
+use crate::virt::VirtContext;
 
 pub type Benchmark = select_env!["MIRALIS_BENCHMARK_TYPE":
     "default"      => default::DefaultBenchmark
@@ -28,9 +29,15 @@ pub trait BenchmarkModule {
         scope: &Scope,
         value: usize,
     );
+
     /// Print formated string with value of the counters
     fn display_counters();
 
+    /// Read the performance counters into the virtual registers.
+    ///
+    /// Note: the specific ABI is depends on the benchmark back-end.
+    fn read_counters(ctx: &mut VirtContext);
+
     fn get_counter_value(counter: Counter) -> usize;
 }
 

src/config.rs

@@ -103,7 +103,7 @@ pub const TARGET_PAYLOAD_ADDRESS: usize =
 pub const TARGET_STACK_SIZE: usize =
     parse_usize_or(option_env!("MIRALIS_TARGET_STACK_SIZE"), 0x8000);
 
-/// The choosen policy name
+/// The chosen policy name
 ///
 /// For now this variable is unused, but we keep it still to force re-compilation when the policy
 /// name changes. We can get rid of it once it becomes possible to track dependencies on

src/lib.rs

@@ -51,7 +51,7 @@ pub unsafe fn main_loop(ctx: &mut VirtContext, mctx: &mut MiralisContext, policy
         Benchmark::stop_interval_counters(Scope::RunVCPU);
         Benchmark::start_interval_counters(Scope::HandleTrap);
 
-        if handle_trap(ctx, mctx, policy) == ExitResult::Donne {
+        if handle_trap(ctx, mctx, policy) == ExitResult::Done {
             return;
         }
 

src/virt/emulator.rs

@@ -26,7 +26,7 @@ pub enum ExitResult {
     /// Continue execution of the virtual firmware or payload.
     Continue,
     /// Terminate execution successfully.
-    Donne,
+    Done,
 }
 
 impl VirtContext {
@@ -510,7 +510,7 @@ impl VirtContext {
                 log::info!("Success!");
                 log::info!("Number of exits: {}", self.nb_exits);
                 // Terminate execution
-                return ExitResult::Donne;
+                return ExitResult::Done;
             }
             abi::MIRALIS_LOG_FID => {
                 let log_level = self.get(Register::X10);
@@ -533,18 +533,21 @@ impl VirtContext {
                     }
                 }
 
-                // For now we don't return error code or the lenght written
+                // For now we don't return error code or the length written
                 self.set(Register::X10, 0);
                 self.set(Register::X11, 0);
-                self.pc += 4;
             }
             abi::MIRALIS_BENCHMARK_FID => {
                 Benchmark::display_counters();
                 Plat::exit_success();
             }
+            abi::MIRALIS_READ_COUNTERS_FID => {
+                Benchmark::read_counters(self);
+            }
             _ => panic!("Invalid Miralis FID: 0x{:x}", fid),
         }
 
+        self.pc += 4;
         ExitResult::Continue
     }
 }