From dbd8d9d474ed12aa618e888415fff345f4d7bca1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fran=C3=A7ois=20Costa?= <frankost.costa@gmail.com>
Date: Sat, 30 Nov 2024 23:09:20 +0100
Subject: [PATCH] SailBugfix: scounteren is read-only except for IR, TMP, and
 CY fields

This commit makes all bits in the mcounteren register read-only, except for the aforementioned IR, TMP, and CY fields, which remain writable.
---
 src/virt/csr.rs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/virt/csr.rs b/src/virt/csr.rs
index 4d9c65a2..34823049 100644
--- a/src/virt/csr.rs
+++ b/src/virt/csr.rs
@@ -520,7 +520,10 @@ impl HwRegisterContextSetter<Csr> for VirtContext {
                     }
                 }
             }
-            Csr::Scounteren => (), // Read-only 0
+            Csr::Scounteren => {
+                // Only show IR, TM and CY (for cycle, time and instret counters)
+                self.csr.scounteren = (self.csr.scounteren & !0b111) | (value & 0b111) as u32
+            }
             Csr::Senvcfg => self.csr.senvcfg = value,
             Csr::Sscratch => self.csr.sscratch = value,
             Csr::Sepc => {