From 43599293d347be1b30d8feb22c4a8c0091ad80b9 Mon Sep 17 00:00:00 2001
From: Andrew Waterman <waterman@eecs.berkeley.edu>
Date: Thu, 6 Feb 2014 03:06:06 -0800
Subject: Improve trap entry code

---
 v/entry.S | 32 ++++++--------------------------
 1 file changed, 6 insertions(+), 26 deletions(-)

(limited to 'v/entry.S')

diff --git a/v/entry.S b/v/entry.S
index 6933771..662c92f 100644
--- a/v/entry.S
+++ b/v/entry.S
@@ -10,10 +10,12 @@
 # define REGBYTES 4
 #endif
 
+#define STACK_TOP (_end + 131072)
+
   .text
   .global _start
 _start:
-  la sp, stack_top
+  la sp, STACK_TOP
   li a1, 1337
   la a0, userstart
   j vm_boot
@@ -66,22 +68,6 @@ save_tf:  # write the trap frame onto the stack
   csrr   x3,cause        # cause
   STORE  x3,35*REGBYTES(x2)
 
-  # get faulting insn, if it wasn't a fetch-related trap
-  li    x5, CAUSE_MISALIGNED_FETCH
-  li    x6, CAUSE_FAULT_FETCH
-  beq   x3, x5, 1f
-  beq   x3, x6, 1f
-  lh    x5,0(x4)
-  lh    x6,2(x4)
-  sh    x5,  36*REGBYTES(x2)
-  sh    x6,2+36*REGBYTES(x2)
-1:
-
-  bge   x3, x0, 1f
-  vxcptcause x3
-  STORE  x3,37*REGBYTES(x2)
-1:
-
   ret
 
   .globl  pop_tf
@@ -143,7 +129,7 @@ trap_entry:
   bnez  ra, 1f
 
   # no, so start at the top of the stack
-  la    x2,stack_top-SIZEOF_TRAPFRAME_T
+  la    x2,STACK_TOP-SIZEOF_TRAPFRAME_T
   jal   save_tf
   move  sp,x2
   csrs  status,SR_EI
@@ -151,7 +137,7 @@ trap_entry:
   csrr  ra,status
   and   ra,ra,SR_EA
   beqz  ra, 2f
-  addi  x2,x2,38*REGBYTES
+  addi  x2,x2,36*REGBYTES
 
   # rocket currently doesn't support vxcptsave/vxcptrestore natively
   csrr  x3,impl 
@@ -177,10 +163,4 @@ trap_entry:
   csrs  status,SR_EI
   move  a0,x2
   jal   handle_trap
-
-  .bss
-  .global stack_bot
-  .global stack_top
-stack_bot:
-  .skip  32768
-stack_top:
+  unimp
-- 
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