Fix PLIC on big-endian hosts

2 files changed, 26 insertions, 3 deletions

diff --git a/riscv/devices.h b/riscv/devices.h
index 0fa8885..f7e631e 100644
--- a/riscv/devices.h
+++ b/riscv/devices.h
@@ -10,6 +10,7 @@
 #include <queue>
 #include <vector>
 #include <utility>
+#include <cassert>
 
 class processor_t;
 class sim_t;
@@ -170,4 +171,26 @@ class mmio_plugin_device_t : public abstract_device_t {
   void* user_data;
 };
 
+template<typename T>
+void write_little_endian_reg(T* word, reg_t addr, size_t len, const uint8_t* bytes)
+{
+  assert(len <= sizeof(T));
+
+  for (size_t i = 0; i < len; i++) {
+    const int shift = 8 * ((addr + i) % sizeof(T));
+    *word = (*word & ~(T(0xFF) << shift)) | (T(bytes[i]) << shift);
+  }
+}
+
+template<typename T>
+void read_little_endian_reg(T word, reg_t addr, size_t len, uint8_t* bytes)
+{
+  assert(len <= sizeof(T));
+
+  for (size_t i = 0; i < len; i++) {
+    const int shift = 8 * ((addr + i) % sizeof(T));
+    bytes[i] = word >> shift;
+  }
+}
+
 #endif
diff --git a/riscv/plic.cc b/riscv/plic.cc
index 57355ef..515451a 100644
--- a/riscv/plic.cc
+++ b/riscv/plic.cc
@@ -329,7 +329,7 @@ bool plic_t::load(reg_t addr, size_t len, uint8_t* bytes)
     }
   }
 
-  memcpy(bytes, (uint8_t *)&val, len);
+  read_little_endian_reg(val, addr, len, bytes);
 
   return ret;
 }
@@ -337,7 +337,7 @@ bool plic_t::load(reg_t addr, size_t len, uint8_t* bytes)
 bool plic_t::store(reg_t addr, size_t len, const uint8_t* bytes)
 {
   bool ret = false;
-  uint32_t val;
+  uint32_t val = 0;
 
   switch (len) {
     case 4:
@@ -350,7 +350,7 @@ bool plic_t::store(reg_t addr, size_t len, const uint8_t* bytes)
       return false;
   }
 
-  memcpy((uint8_t *)&val, bytes, len);
+  write_little_endian_reg(&val, addr, len, bytes);
 
   if (PRIORITY_BASE <= addr && addr < ENABLE_BASE) {
     ret = priority_write(addr, val);