From 27498013ad7684a5f22a99790ac29badea205a3f Mon Sep 17 00:00:00 2001
From: Palmer Dabbelt <palmer@dabbelt.com>
Date: Thu, 2 Nov 2017 18:22:37 -0700
Subject: Check if we have extensions before using them

---
 machine/minit.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/machine/minit.c b/machine/minit.c
index a324d06..5f98501 100644
--- a/machine/minit.c
+++ b/machine/minit.c
@@ -19,22 +19,28 @@ size_t plic_ndevs;
 static void mstatus_init()
 {
   // Enable FPU
-  write_csr(mstatus, MSTATUS_FS);
+  if (supports_extension('D') || supports_extension('F'))
+    write_csr(mstatus, MSTATUS_FS);
 
   // Enable user/supervisor use of perf counters
-  write_csr(scounteren, -1);
+  if (supports_extension('S'))
+    write_csr(scounteren, -1);
   write_csr(mcounteren, -1);
 
   // Enable software interrupts
   write_csr(mie, MIP_MSIP);
 
   // Disable paging
-  write_csr(sptbr, 0);
+  if (supports_extension('S'))
+    write_csr(sptbr, 0);
 }
 
 // send S-mode interrupts and most exceptions straight to S-mode
 static void delegate_traps()
 {
+  if (!supports_extension('S'))
+    return;
+
   uintptr_t interrupts = MIP_SSIP | MIP_STIP | MIP_SEIP;
   uintptr_t exceptions =
     (1U << CAUSE_MISALIGNED_FETCH) |
@@ -53,11 +59,12 @@ static void delegate_traps()
 
 static void fp_init()
 {
+  if (!supports_extension('D') && !supports_extension('F'))
+    return;
+
   assert(read_csr(mstatus) & MSTATUS_FS);
 
 #ifdef __riscv_flen
-  if (!supports_extension('D'))
-    die("FPU not found; recompile pk with -msoft-float");
   for (int i = 0; i < 32; i++)
     init_fp_reg(i);
   write_csr(fcsr, 0);
-- 
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