From ae7348b246bc091f5af844a7bdaf1044cac90635 Mon Sep 17 00:00:00 2001
From: Marcus Comstedt <marcus@mc.pp.se>
Date: Wed, 16 Jun 2021 22:49:50 +0200
Subject: Set desired endianness at boot time (#247)

---
 machine/mentry.S | 11 +++++++++++
 machine/minit.c  | 16 ++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/machine/mentry.S b/machine/mentry.S
index e71745c..4cf9685 100644
--- a/machine/mentry.S
+++ b/machine/mentry.S
@@ -255,6 +255,17 @@ do_reset:
   li x31, 0
   csrw mscratch, x0
 
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+  # fixup endianness before making any loads or stores
+#if __riscv_xlen == 32
+  li t0, MSTATUSH_MBE
+  csrs CSR_MSTATUSH, t0
+#else
+  li t0, MSTATUS_MBE
+  csrs CSR_MSTATUS, t0
+#endif
+#endif
+
   # write mtvec and make sure it sticks
   la t0, trap_vector
   csrw mtvec, t0
diff --git a/machine/minit.c b/machine/minit.c
index c519926..d35f9df 100644
--- a/machine/minit.c
+++ b/machine/minit.c
@@ -24,6 +24,19 @@ void* kernel_end;
 static void mstatus_init()
 {
   uintptr_t mstatus = 0;
+#if __riscv_xlen == 32
+  uint32_t mstatush = 0;
+#endif
+
+  // Set endianness
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#if __riscv_xlen == 32
+  mstatush |= MSTATUSH_SBE | MSTATUSH_MBE;
+#else
+  mstatus |= MSTATUS_SBE | MSTATUS_MBE;
+#endif
+  mstatus |= MSTATUS_UBE;
+#endif
 
   // Enable FPU
   if (supports_extension('F'))
@@ -34,6 +47,9 @@ static void mstatus_init()
     mstatus |= MSTATUS_VS;
 
   write_csr(mstatus, mstatus);
+#if __riscv_xlen == 32 && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+  write_csr(0x310, mstatush); /* mstatush is not known to gas */
+#endif
 
   // Enable user/supervisor use of perf counters
   if (supports_extension('S'))
-- 
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