Stop using mtohost/mfromhost registers

2 files changed, 16 insertions, 30 deletions

diff --git a/v/entry.S b/v/entry.S
index 64d9606..460428a 100644
--- a/v/entry.S
+++ b/v/entry.S
@@ -22,13 +22,6 @@ nmi_vector:
   j wtf
 
 trap_vector:
-  # we can safely clobber caller-saved registers here, because we were
-  # either invoked via do_tohost or we are about to bail out
-  csrr t0, mcause
-  li t1, CAUSE_SUPERVISOR_ECALL
-  beq t0, t1, handle_tohost
-  li t1, CAUSE_MACHINE_ECALL
-  beq t0, t1, handle_tohost
   j wtf
 
 handle_reset:
@@ -128,25 +121,3 @@ trap_entry:
 
   move  a0, sp
   j handle_trap
-
-  .global do_tohost
-do_tohost:
-  ecall
-  ret
-
-handle_tohost:
-1:csrrw t0, mtohost, a0
-  bnez t0, 1b
-
-1:csrrw t0, mfromhost, x0
-  bnez t0, 1b
-
-  csrr t0, mepc
-  addi t0, t0, 4
-  csrw mepc, t0
-  mret
-
-wtf:
-  li a0, 841
-1:csrw mtohost, a0
-  j 1b
diff --git a/v/vm.c b/v/vm.c
index ef1f733..5fd1b11 100644
--- a/v/vm.c
+++ b/v/vm.c
@@ -8,7 +8,17 @@
 
 void trap_entry();
 void pop_tf(trapframe_t*);
-void do_tohost(long tohost_value);
+
+volatile uint64_t tohost __attribute__((aligned(64)));
+volatile uint64_t fromhost __attribute__((aligned(64)));
+
+static void do_tohost(uint64_t tohost_value)
+{
+  tohost = tohost_value;
+  while (fromhost == 0)
+    ;
+  fromhost = 0;
+}
 
 #define pa2kva(pa) ((void*)(pa) - DRAM_BASE - MEGAPAGE_SIZE)
 #define uva2kva(pa) ((void*)(pa) - MEGAPAGE_SIZE)
@@ -36,6 +46,11 @@ static void terminate(int code)
   while (1);
 }
 
+void wtf()
+{
+  terminate(841);
+}
+
 #define stringify1(x) #x
 #define stringify(x) stringify1(x)
 #define assert(x) do { \