From ed0d99f10cfbdff629a3578d1c29882613143029 Mon Sep 17 00:00:00 2001
From: Greg Chadwick <gac@lowrisc.org>
Date: Wed, 16 Nov 2022 16:45:14 +0000
Subject: [PATCH] Attempt access on every byte of an unaligned access

To match Ibex behaviour this updates the spike unaligned load/store
behaviour to try accessing all bytes rather than stopping as soon as an
error is seen. If one or more errors are seen whilst accessing these
bytes the first one is thrown.
---
 riscv/mmu.h | 41 +++++++++++++++++++++++++++++++++++++----
 1 file changed, 37 insertions(+), 4 deletions(-)

diff --git a/riscv/mmu.h b/riscv/mmu.h
index b3c38c230b..b4abc2e3d0 100644
--- a/riscv/mmu.h
+++ b/riscv/mmu.h
@@ -56,8 +56,25 @@ class mmu_t
   {
 #ifdef RISCV_ENABLE_MISALIGNED
     reg_t res = 0;
-    for (size_t i = 0; i < size; i++)
-      res += (reg_t)load_uint8(addr + (target_big_endian? size-1-i : i)) << (i * 8);
+    bool caught_fault = false;
+    trap_load_access_fault fault(false, 0, 0, 0);
+    for (size_t i = 0; i < size; i++) {
+      try {
+        res += (reg_t)load_uint8(addr + (target_big_endian? size-1-i : i)) << (i * 8);
+      } catch (trap_load_access_fault& f) {
+        if (!caught_fault) {
+          // Catch first fault seen on unaligned access and proceed with other bytes of the access.
+          fault = f;
+          caught_fault = true;
+        }
+      }
+    }
+
+    if (caught_fault) {
+      // Throw a fault if we saw onw
+      throw fault;
+    }
+
     return res;
 #else
     bool gva = ((proc) ? proc->state.v : false) || (RISCV_XLATE_VIRT & xlate_flags);
@@ -68,8 +85,24 @@ class mmu_t
   inline void misaligned_store(reg_t addr, reg_t data, size_t size, uint32_t xlate_flags, bool actually_store=true)
   {
 #ifdef RISCV_ENABLE_MISALIGNED
-    for (size_t i = 0; i < size; i++)
-      store_uint8(addr + (target_big_endian? size-1-i : i), data >> (i * 8), actually_store);
+    bool caught_fault = false;
+    trap_store_access_fault fault(false, 0, 0, 0);
+    for (size_t i = 0; i < size; i++) {
+      try {
+        store_uint8(addr + (target_big_endian? size-1-i : i), data >> (i * 8), actually_store);
+      } catch (trap_store_access_fault& f) {
+        if (!caught_fault) {
+          // Catch first fault seen on unaligned access and proceed with other bytes of the access.
+          fault = f;
+          caught_fault = true;
+        }
+      }
+    }
+
+    if (caught_fault) {
+      // Throw a fault if we saw onw
+      throw fault;
+    }
 #else
     bool gva = ((proc) ? proc->state.v : false) || (RISCV_XLATE_VIRT & xlate_flags);
     throw trap_store_address_misaligned(gva, addr, 0, 0);