Add perf_counters test

- At the moment, this only tests mcycle / mcycleh. As Kelvin gets more
  perf counters, we can expand this test suite.

Change-Id: Ia96b183ffd323fa9333bfa3792aa051e66714a84

tests/kelvin_isa/BUILD

diff --git a/tests/kelvin_isa/BUILD b/tests/kelvin_isa/BUILD
index 52865ac..1584d83 100644
--- a/tests/kelvin_isa/BUILD
+++ b/tests/kelvin_isa/BUILD
@@ -25,6 +25,17 @@
 )
 
 kelvin_test(
+    name = "perf_counters",
+    srcs = [
+        "perf_counters.cc",
+    ],
+    hw_test_size = "small",
+    deps = [
+        ":kelvin_test",
+    ],
+)
+
+kelvin_test(
     name = "acset",
     srcs = [
         "acset.cc",

tests/kelvin_isa/perf_counters.cc

diff --git a/tests/kelvin_isa/perf_counters.cc b/tests/kelvin_isa/perf_counters.cc
new file mode 100644
index 0000000..937f820
--- /dev/null
+++ b/tests/kelvin_isa/perf_counters.cc
@@ -0,0 +1,56 @@
+/*
+ * Copyright 2024 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <cstdio>
+#include <cstdint>
+
+#include "tests/kelvin_isa/kelvin_test.h"
+
+inline uint64_t mcycle_read(void) {
+  uint32_t cycle_low = 0;
+  uint32_t cycle_high = 0;
+  asm volatile(
+      "1:"
+      "  csrr %0, mcycleh;"  // Read `mcycleh`.
+      "  csrr %1, mcycle;"   // Read `mcycle`.
+      : "=r"(cycle_high), "=r"(cycle_low)
+      :);
+  return static_cast<uint64_t>(cycle_high) << 32 | cycle_low;
+}
+
+int main(void) {
+    // Set the cycle counter to 0x1ffffffff.
+    asm volatile (" \
+        csrwi mcycleh, 1; \
+        li a0, 0xfffffffd; \
+        csrrw a0, mcycle, a0;" : /* no outputs*/ : /* no inputs */ : /* clobbers */"a0");
+    uint64_t cycle = mcycle_read();
+    uint64_t cycle2 = mcycle_read();
+    uint32_t cycle_lo, cycle_hi, cycle2_lo, cycle2_hi;
+    cycle_lo = cycle & 0xFFFFFFFF;
+    cycle2_lo = cycle2 & 0xFFFFFFFF;
+    cycle_hi = cycle >> 32;
+    cycle2_hi = cycle2 >> 32;
+    if (cycle2_hi == cycle_hi) {
+        printf("mcycleh did not increment\r\n");
+        exit(-1);
+    }
+    if (cycle2_lo > cycle_lo) {
+        printf("mcycle did not wrap");
+        exit(-1);
+    }
+    return 0;
+}