Synced up PK with supervisor changes/asm syntax

You must upgrade to the latest compiler and ISA
simulator to build and run this version of the PK.

10 files changed, 229 insertions, 274 deletions

diff --git a/pk/entry.S b/pk/entry.S
index 6f0d1a0..ee47b41 100644
--- a/pk/entry.S
+++ b/pk/entry.S
@@ -15,60 +15,60 @@
 save_tf:  # write the trap frame onto the stack
 
   # save gprs
-  STORE  $x3,3*REGBYTES($x2)
-  STORE  $x4,4*REGBYTES($x2)
-  STORE  $x5,5*REGBYTES($x2)
-  STORE  $x6,6*REGBYTES($x2)
-  STORE  $x7,7*REGBYTES($x2)
-  STORE  $x8,8*REGBYTES($x2)
-  STORE  $x9,9*REGBYTES($x2)
-  STORE  $x10,10*REGBYTES($x2)
-  STORE  $x11,11*REGBYTES($x2)
-  STORE  $x12,12*REGBYTES($x2)
-  STORE  $x13,13*REGBYTES($x2)
-  STORE  $x14,14*REGBYTES($x2)
-  STORE  $x15,15*REGBYTES($x2)
-  STORE  $x16,16*REGBYTES($x2)
-  STORE  $x17,17*REGBYTES($x2)
-  STORE  $x18,18*REGBYTES($x2)
-  STORE  $x19,19*REGBYTES($x2)
-  STORE  $x20,20*REGBYTES($x2)
-  STORE  $x21,21*REGBYTES($x2)
-  STORE  $x22,22*REGBYTES($x2)
-  STORE  $x23,23*REGBYTES($x2)
-  STORE  $x24,24*REGBYTES($x2)
-  STORE  $x25,25*REGBYTES($x2)
-  STORE  $x26,26*REGBYTES($x2)
-  STORE  $x27,27*REGBYTES($x2)
-  STORE  $x28,28*REGBYTES($x2)
-  STORE  $x29,29*REGBYTES($x2)
-  STORE  $x30,30*REGBYTES($x2)
-  STORE  $x31,31*REGBYTES($x2)
+  STORE  x3,3*REGBYTES(x2)
+  STORE  x4,4*REGBYTES(x2)
+  STORE  x5,5*REGBYTES(x2)
+  STORE  x6,6*REGBYTES(x2)
+  STORE  x7,7*REGBYTES(x2)
+  STORE  x8,8*REGBYTES(x2)
+  STORE  x9,9*REGBYTES(x2)
+  STORE  x10,10*REGBYTES(x2)
+  STORE  x11,11*REGBYTES(x2)
+  STORE  x12,12*REGBYTES(x2)
+  STORE  x13,13*REGBYTES(x2)
+  STORE  x14,14*REGBYTES(x2)
+  STORE  x15,15*REGBYTES(x2)
+  STORE  x16,16*REGBYTES(x2)
+  STORE  x17,17*REGBYTES(x2)
+  STORE  x18,18*REGBYTES(x2)
+  STORE  x19,19*REGBYTES(x2)
+  STORE  x20,20*REGBYTES(x2)
+  STORE  x21,21*REGBYTES(x2)
+  STORE  x22,22*REGBYTES(x2)
+  STORE  x23,23*REGBYTES(x2)
+  STORE  x24,24*REGBYTES(x2)
+  STORE  x25,25*REGBYTES(x2)
+  STORE  x26,26*REGBYTES(x2)
+  STORE  x27,27*REGBYTES(x2)
+  STORE  x28,28*REGBYTES(x2)
+  STORE  x29,29*REGBYTES(x2)
+  STORE  x30,30*REGBYTES(x2)
+  STORE  x31,31*REGBYTES(x2)
 
-  mfpcr  $x3,ASM_CR(PCR_K0)
-  STORE  $x3,1*REGBYTES($x2)          # $x1 is in $PCR_K0
-  mfpcr  $x3,ASM_CR(PCR_K1)
-  STORE  $x3,2*REGBYTES($x2)          # $x2 is in $PCR_K1
+  mfpcr  x3,ASM_CR(PCR_K0)
+  STORE  x3,1*REGBYTES(x2)          # x1 is in PCR_K0
+  mfpcr  x3,ASM_CR(PCR_K1)
+  STORE  x3,2*REGBYTES(x2)          # x2 is in PCR_K1
 
   # get sr, epc, badvaddr, cause
-  mfpcr  $x3,ASM_CR(PCR_SR)          # sr
-  STORE  $x3,32*REGBYTES($x2)
-  mfpcr  $x4,ASM_CR(PCR_EPC)          # epc
-  STORE  $x4,33*REGBYTES($x2)
-  mfpcr  $x3,ASM_CR(PCR_BADVADDR)      # badvaddr
-  STORE  $x3,34*REGBYTES($x2)
-  mfpcr  $x3,ASM_CR(PCR_CAUSE)        # cause
-  STORE  $x3,35*REGBYTES($x2)
+  mfpcr  x3,ASM_CR(PCR_SR)          # sr
+  STORE  x3,32*REGBYTES(x2)
+  mfpcr  x4,ASM_CR(PCR_EPC)          # epc
+  STORE  x4,33*REGBYTES(x2)
+  mfpcr  x3,ASM_CR(PCR_BADVADDR)      # badvaddr
+  STORE  x3,34*REGBYTES(x2)
+  mfpcr  x3,ASM_CR(PCR_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    $x3,0($x4)
-  lh    $x4,2($x4)
-  sh    $x3,  36*REGBYTES($x2)
-  sh    $x4,2+36*REGBYTES($x2)
+  li    x5, CAUSE_MISALIGNED_FETCH
+  li    x6, CAUSE_FAULT_FETCH
+  beq   x3, x5, 1f
+  beq   x3, x6, 1f
+  lh    x3,0(x4)
+  lh    x4,2(x4)
+  sh    x3,  36*REGBYTES(x2)
+  sh    x4,2+36*REGBYTES(x2)
 1:
   ret
   .end  save_tf
@@ -77,68 +77,68 @@ save_tf:  # write the trap frame onto the stack
   .ent  pop_tf
 pop_tf:  # write the trap frame onto the stack
   # restore gprs
-  LOAD  $t0,32*REGBYTES($a0)  # restore sr (should disable interrupts)
-  mtpcr  $t0,ASM_CR(PCR_SR)
+  LOAD  t0,32*REGBYTES(a0)  # restore sr (should disable interrupts)
+  mtpcr  t0,ASM_CR(PCR_SR)
 
-  LOAD  $x1,1*REGBYTES($a0)
-  mtpcr  $x1,ASM_CR(PCR_K0)
-  LOAD  $x1,2*REGBYTES($a0)
-  mtpcr $x1,ASM_CR(PCR_K1)
-  move  $x1,$a0
-  LOAD  $x3,3*REGBYTES($x1)
-  LOAD  $x4,4*REGBYTES($x1)
-  LOAD  $x5,5*REGBYTES($x1)
-  LOAD  $x6,6*REGBYTES($x1)
-  LOAD  $x7,7*REGBYTES($x1)
-  LOAD  $x8,8*REGBYTES($x1)
-  LOAD  $x9,9*REGBYTES($x1)
-  LOAD  $x10,10*REGBYTES($x1)
-  LOAD  $x11,11*REGBYTES($x1)
-  LOAD  $x12,12*REGBYTES($x1)
-  LOAD  $x13,13*REGBYTES($x1)
-  LOAD  $x14,14*REGBYTES($x1)
-  LOAD  $x15,15*REGBYTES($x1)
-  LOAD  $x16,16*REGBYTES($x1)
-  LOAD  $x17,17*REGBYTES($x1)
-  LOAD  $x18,18*REGBYTES($x1)
-  LOAD  $x19,19*REGBYTES($x1)
-  LOAD  $x20,20*REGBYTES($x1)
-  LOAD  $x21,21*REGBYTES($x1)
-  LOAD  $x22,22*REGBYTES($x1)
-  LOAD  $x23,23*REGBYTES($x1)
-  LOAD  $x24,24*REGBYTES($x1)
-  LOAD  $x25,25*REGBYTES($x1)
-  LOAD  $x26,26*REGBYTES($x1)
-  LOAD  $x27,27*REGBYTES($x1)
-  LOAD  $x28,28*REGBYTES($x1)
-  LOAD  $x29,29*REGBYTES($x1)
-  LOAD  $x30,30*REGBYTES($x1)
-  LOAD  $x31,31*REGBYTES($x1)
+  LOAD  x1,1*REGBYTES(a0)
+  mtpcr  x1,ASM_CR(PCR_K0)
+  LOAD  x1,2*REGBYTES(a0)
+  mtpcr x1,ASM_CR(PCR_K1)
+  move  x1,a0
+  LOAD  x3,3*REGBYTES(x1)
+  LOAD  x4,4*REGBYTES(x1)
+  LOAD  x5,5*REGBYTES(x1)
+  LOAD  x6,6*REGBYTES(x1)
+  LOAD  x7,7*REGBYTES(x1)
+  LOAD  x8,8*REGBYTES(x1)
+  LOAD  x9,9*REGBYTES(x1)
+  LOAD  x10,10*REGBYTES(x1)
+  LOAD  x11,11*REGBYTES(x1)
+  LOAD  x12,12*REGBYTES(x1)
+  LOAD  x13,13*REGBYTES(x1)
+  LOAD  x14,14*REGBYTES(x1)
+  LOAD  x15,15*REGBYTES(x1)
+  LOAD  x16,16*REGBYTES(x1)
+  LOAD  x17,17*REGBYTES(x1)
+  LOAD  x18,18*REGBYTES(x1)
+  LOAD  x19,19*REGBYTES(x1)
+  LOAD  x20,20*REGBYTES(x1)
+  LOAD  x21,21*REGBYTES(x1)
+  LOAD  x22,22*REGBYTES(x1)
+  LOAD  x23,23*REGBYTES(x1)
+  LOAD  x24,24*REGBYTES(x1)
+  LOAD  x25,25*REGBYTES(x1)
+  LOAD  x26,26*REGBYTES(x1)
+  LOAD  x27,27*REGBYTES(x1)
+  LOAD  x28,28*REGBYTES(x1)
+  LOAD  x29,29*REGBYTES(x1)
+  LOAD  x30,30*REGBYTES(x1)
+  LOAD  x31,31*REGBYTES(x1)
 
   # gtfo!
-  LOAD  $x2,33*REGBYTES($x1)
-  mtpcr $x2,ASM_CR(PCR_EPC)
-  mfpcr $x1,ASM_CR(PCR_K0)
-  mfpcr $x2,ASM_CR(PCR_K1)
+  LOAD  x2,33*REGBYTES(x1)
+  mtpcr x2,ASM_CR(PCR_EPC)
+  mfpcr x1,ASM_CR(PCR_K0)
+  mfpcr x2,ASM_CR(PCR_K1)
   eret
   .end  pop_tf
 
   .global  trap_entry
   .ent  trap_entry
 trap_entry:
-  mtpcr $ra,ASM_CR(PCR_K0)
-  mtpcr $x2,ASM_CR(PCR_K1)
+  mtpcr ra,ASM_CR(PCR_K0)
+  mtpcr x2,ASM_CR(PCR_K1)
 
   # when coming from kernel, continue below its stack
-  mfpcr $ra,ASM_CR(PCR_SR)
-  and   $ra,$ra,SR_PS
-  add   $x2, $sp, -320
-  bnez  $ra, 1f
-  la    $x2,stack_top-320
+  mfpcr ra,ASM_CR(PCR_SR)
+  and   ra,ra,SR_PS
+  add   x2, sp, -320
+  bnez  ra, 1f
+  la    x2,stack_top-320
 
 1:jal   save_tf
-  move  $sp,$x2
-  move  $a0,$x2
+  move  sp,x2
+  move  a0,x2
   jal    handle_trap
   .end  trap_entry
 
diff --git a/pk/fp_asm.S b/pk/fp_asm.S
index c6c8bba..0c2df13 100644
--- a/pk/fp_asm.S
+++ b/pk/fp_asm.S
@@ -5,40 +5,40 @@
 	.ent	get_fp_state
 get_fp_state:
 
-	mffsr	$v0
+	mffsr	v0
 
-	fsd		$f0 ,  0($a0)
-	fsd		$f1 ,  8($a0)
-	fsd		$f2 , 16($a0)
-	fsd		$f3 , 24($a0)
-	fsd		$f4 , 32($a0)
-	fsd		$f5 , 40($a0)
-	fsd		$f6 , 48($a0)
-	fsd		$f7 , 56($a0)
-	fsd		$f8 , 64($a0)
-	fsd		$f9 , 72($a0)
-	fsd		$f10, 80($a0)
-	fsd		$f11, 88($a0)
-	fsd		$f12, 96($a0)
-	fsd		$f13,104($a0)
-	fsd		$f14,112($a0)
-	fsd		$f15,120($a0)
-	fsd		$f16,128($a0)
-	fsd		$f17,136($a0)
-	fsd		$f18,144($a0)
-	fsd		$f19,152($a0)
-	fsd		$f20,160($a0)
-	fsd		$f21,168($a0)
-	fsd		$f22,176($a0)
-	fsd		$f23,184($a0)
-	fsd		$f24,192($a0)
-	fsd		$f25,200($a0)
-	fsd		$f26,208($a0)
-	fsd		$f27,216($a0)
-	fsd		$f28,224($a0)
-	fsd		$f29,232($a0)
-	fsd		$f30,240($a0)
-	fsd		$f31,248($a0)
+	fsd		f0 ,  0(a0)
+	fsd		f1 ,  8(a0)
+	fsd		f2 , 16(a0)
+	fsd		f3 , 24(a0)
+	fsd		f4 , 32(a0)
+	fsd		f5 , 40(a0)
+	fsd		f6 , 48(a0)
+	fsd		f7 , 56(a0)
+	fsd		f8 , 64(a0)
+	fsd		f9 , 72(a0)
+	fsd		f10, 80(a0)
+	fsd		f11, 88(a0)
+	fsd		f12, 96(a0)
+	fsd		f13,104(a0)
+	fsd		f14,112(a0)
+	fsd		f15,120(a0)
+	fsd		f16,128(a0)
+	fsd		f17,136(a0)
+	fsd		f18,144(a0)
+	fsd		f19,152(a0)
+	fsd		f20,160(a0)
+	fsd		f21,168(a0)
+	fsd		f22,176(a0)
+	fsd		f23,184(a0)
+	fsd		f24,192(a0)
+	fsd		f25,200(a0)
+	fsd		f26,208(a0)
+	fsd		f27,216(a0)
+	fsd		f28,224(a0)
+	fsd		f29,232(a0)
+	fsd		f30,240(a0)
+	fsd		f31,248(a0)
 
 	ret
 
@@ -48,40 +48,40 @@ get_fp_state:
 	.ent	put_fp_state
 put_fp_state:
 
-	fld		$f0 ,  0($a0)
-	fld		$f1 ,  8($a0)
-	fld		$f2 , 16($a0)
-	fld		$f3 , 24($a0)
-	fld		$f4 , 32($a0)
-	fld		$f5 , 40($a0)
-	fld		$f6 , 48($a0)
-	fld		$f7 , 56($a0)
-	fld		$f8 , 64($a0)
-	fld		$f9 , 72($a0)
-	fld		$f10, 80($a0)
-	fld		$f11, 88($a0)
-	fld		$f12, 96($a0)
-	fld		$f13,104($a0)
-	fld		$f14,112($a0)
-	fld		$f15,120($a0)
-	fld		$f16,128($a0)
-	fld		$f17,136($a0)
-	fld		$f18,144($a0)
-	fld		$f19,152($a0)
-	fld		$f20,160($a0)
-	fld		$f21,168($a0)
-	fld		$f22,176($a0)
-	fld		$f23,184($a0)
-	fld		$f24,192($a0)
-	fld		$f25,200($a0)
-	fld		$f26,208($a0)
-	fld		$f27,216($a0)
-	fld		$f28,224($a0)
-	fld		$f29,232($a0)
-	fld		$f30,240($a0)
-	fld		$f31,248($a0)
+	fld		f0 ,  0(a0)
+	fld		f1 ,  8(a0)
+	fld		f2 , 16(a0)
+	fld		f3 , 24(a0)
+	fld		f4 , 32(a0)
+	fld		f5 , 40(a0)
+	fld		f6 , 48(a0)
+	fld		f7 , 56(a0)
+	fld		f8 , 64(a0)
+	fld		f9 , 72(a0)
+	fld		f10, 80(a0)
+	fld		f11, 88(a0)
+	fld		f12, 96(a0)
+	fld		f13,104(a0)
+	fld		f14,112(a0)
+	fld		f15,120(a0)
+	fld		f16,128(a0)
+	fld		f17,136(a0)
+	fld		f18,144(a0)
+	fld		f19,152(a0)
+	fld		f20,160(a0)
+	fld		f21,168(a0)
+	fld		f22,176(a0)
+	fld		f23,184(a0)
+	fld		f24,192(a0)
+	fld		f25,200(a0)
+	fld		f26,208(a0)
+	fld		f27,216(a0)
+	fld		f28,224(a0)
+	fld		f29,232(a0)
+	fld		f30,240(a0)
+	fld		f31,248(a0)
 
-	mtfsr	$a1
+	mtfsr	a1
 
 	ret
 
diff --git a/pk/handlers.c b/pk/handlers.c
index ebc8f2a..fee9a51 100644
--- a/pk/handlers.c
+++ b/pk/handlers.c
@@ -99,30 +99,9 @@ void handle_fault_store(trapframe_t* tf)
   panic("Faulting store!");
 }
 
-static void handle_bad_interrupt(trapframe_t* tf, int interrupt)
-{
-  panic("Bad interrupt %d!",interrupt);
-}
-
 static void handle_timer_interrupt(trapframe_t* tf)
 {
-  mtpcr(PCR_COMPARE, mfpcr(PCR_COMPARE)+TIMER_PERIOD);
-}
-
-static void handle_interrupt(trapframe_t* tf)
-{
-  int interrupts = (tf->cause & CAUSE_IP) >> CAUSE_IP_SHIFT;
-
-  for(int i = 0; interrupts; interrupts >>= 1, i++)
-  {
-    if(interrupts & 1)
-    {
-      if(i == TIMER_IRQ)
-        handle_timer_interrupt(tf);
-      else
-        handle_bad_interrupt(tf,i);
-    }
-  }
+  panic("Timer interrupt!");
 }
 
 static void handle_syscall(trapframe_t* tf)
@@ -148,7 +127,6 @@ void handle_trap(trapframe_t* tf)
     [CAUSE_ILLEGAL_INSTRUCTION] = handle_illegal_instruction,
     [CAUSE_PRIVILEGED_INSTRUCTION] = handle_privileged_instruction,
     [CAUSE_FP_DISABLED] = handle_fp_disabled,
-    [CAUSE_INTERRUPT] = handle_interrupt,
     [CAUSE_SYSCALL] = handle_syscall,
     [CAUSE_BREAKPOINT] = handle_breakpoint,
     [CAUSE_MISALIGNED_LOAD] = handle_misaligned_load,
@@ -158,12 +136,12 @@ void handle_trap(trapframe_t* tf)
     [CAUSE_VECTOR_DISABLED] = handle_vector_disabled,
     [CAUSE_VECTOR_BANK] = handle_vector_bank,
     [CAUSE_VECTOR_ILLEGAL_INSTRUCTION] = handle_vector_illegal_instruction,
+    [CAUSE_IRQ0 + TIMER_IRQ] = handle_timer_interrupt,
   };
 
-  int exccode = (tf->cause & CAUSE_EXCCODE) >> CAUSE_EXCCODE_SHIFT;
-  kassert(exccode < ARRAY_SIZE(trap_handlers));
+  kassert(tf->cause < ARRAY_SIZE(trap_handlers) && trap_handlers[tf->cause]);
 
-  trap_handlers[exccode](tf);
+  trap_handlers[tf->cause](tf);
 
   pop_tf(tf);
 }
diff --git a/pk/pcr.h b/pk/pcr.h
index b463a16..c70b6c4 100644
--- a/pk/pcr.h
+++ b/pk/pcr.h
@@ -1,8 +1,6 @@
 #ifndef _RISCV_COP0_H
 #define _RISCV_COP0_H
 
-#include "config.h"
-
 #define SR_ET    0x0000000000000001
 #define SR_EF    0x0000000000000002
 #define SR_EV    0x0000000000000004
@@ -12,6 +10,9 @@
 #define SR_UX    0x0000000000000040
 #define SR_SX    0x0000000000000080
 #define SR_IM    0x000000000000FF00
+#define SR_VM    0x0000000000010000
+
+#define SR_IM_SHIFT 8
 
 #define PCR_SR       0
 #define PCR_EPC      1
@@ -20,32 +21,24 @@
 #define PCR_COUNT    4
 #define PCR_COMPARE  5
 #define PCR_CAUSE    6
-#define PCR_MEMSIZE  8
+#define PCR_PTBR     7
+#define PCR_SEND_IPI 8
+#define PCR_CLR_IPI  9
+#define PCR_COREID   10
+#define PCR_K0       12
+#define PCR_K1       13
 #define PCR_TOHOST   16
 #define PCR_FROMHOST 17
 #define PCR_CONSOLE  18
-#define PCR_K0       24
-#define PCR_K1       25
-
-#define CR_FSR       0
-#define CR_TID       29
-
-#define MEMSIZE_SHIFT 12
 
-#define TIMER_PERIOD 0x1000
+#define IPI_IRQ   5
 #define TIMER_IRQ 7
 
-#define CAUSE_EXCCODE 0x000000FF
-#define CAUSE_IP      0x0000FF00
-#define CAUSE_EXCCODE_SHIFT 0
-#define CAUSE_IP_SHIFT      8
-
 #define CAUSE_MISALIGNED_FETCH 0
 #define CAUSE_FAULT_FETCH 1
 #define CAUSE_ILLEGAL_INSTRUCTION 2
 #define CAUSE_PRIVILEGED_INSTRUCTION 3
 #define CAUSE_FP_DISABLED 4
-#define CAUSE_INTERRUPT 5
 #define CAUSE_SYSCALL 6
 #define CAUSE_BREAKPOINT 7
 #define CAUSE_MISALIGNED_LOAD 8
@@ -55,25 +48,26 @@
 #define CAUSE_VECTOR_DISABLED 12
 #define CAUSE_VECTOR_BANK 13
 #define CAUSE_VECTOR_ILLEGAL_INSTRUCTION 14
-#define NUM_CAUSES 15
+#define CAUSE_IRQ0 16
+#define CAUSE_IRQ1 17
+#define CAUSE_IRQ2 18
+#define CAUSE_IRQ3 19
+#define CAUSE_IRQ4 20
+#define CAUSE_IRQ5 21
+#define CAUSE_IRQ6 22
+#define CAUSE_IRQ7 23
+#define NUM_CAUSES 24
 
 #define ASM_CR(r)   _ASM_CR(r)
-#define _ASM_CR(r)  $cr##r
+#define _ASM_CR(r)  cr##r
 
 #ifndef __ASSEMBLER__
 
 #define mtpcr(reg,val) ({ long __tmp = (long)(val); \
-          asm volatile ("mtpcr %0,$cr%1"::"r"(__tmp),"i"(reg)); })
+          asm volatile ("mtpcr %0,cr%1"::"r"(__tmp),"i"(reg)); })
 
 #define mfpcr(reg) ({ long __tmp; \
-          asm volatile ("mfpcr %0,$cr%1" : "=r"(__tmp) : "i"(reg)); \
-          __tmp; })
-
-#define mtcr(reg,val) ({ long __tmp = (long)(val); \
-          asm volatile ("mtcr %0,$cr%1"::"r"(__tmp),"i"(reg)); })
-
-#define mfcr(reg) ({ long __tmp; \
-          asm volatile ("mfcr %0,$cr%1" : "=r"(__tmp) : "i"(reg)); \
+          asm volatile ("mfpcr %0,cr%1" : "=r"(__tmp) : "i"(reg)); \
           __tmp; })
 
 #define irq_disable() asm volatile("di")
diff --git a/pk/pk.c b/pk/pk.c
index 7260601..33b0bda 100644
--- a/pk/pk.c
+++ b/pk/pk.c
@@ -164,14 +164,20 @@ static void jump_usrstart(const char* fn, long sp)
   pop_tf(&tf);
 }
 
+uint32_t mem_mb;
+
 void boot()
 {
   bss_init();
   file_init();
 
-  long stack_top = (mfpcr(PCR_MEMSIZE) << MEMSIZE_SHIFT);
-  if(stack_top >= 0x80000000)
-    stack_top = 0x80000000;
+  // word 0 of memory contains # of MB of memory
+  mem_mb = *(uint32_t*)0;
+
+  unsigned long stack_top = 0x80000000;
+  if (mem_mb < stack_top / (1024 * 1024))
+    stack_top = mem_mb * (1024 * 1024);
+
   stack_top -= USER_MAINVARS_SIZE;
 
   struct args* args = mainvars_init(stack_top);
diff --git a/pk/pk.h b/pk/pk.h
index f7cee78..4c343a5 100644
--- a/pk/pk.h
+++ b/pk/pk.h
@@ -28,6 +28,7 @@ extern "C" {
 
 extern int have_fp;
 extern int have_vector;
+extern uint32_t mem_mb;
 int emulate_fp(trapframe_t*);
 void init_fp(trapframe_t* tf);
 
diff --git a/pk/pk.ld b/pk/pk.ld
index 5be7ab8..5f00253 100644
--- a/pk/pk.ld
+++ b/pk/pk.ld
@@ -1,6 +1,6 @@
-OUTPUT_ARCH( "mips:riscv" )
+OUTPUT_ARCH( "riscv" )
 
-ENTRY( __start )
+ENTRY( _start )
 
 SECTIONS
 {
@@ -10,7 +10,7 @@ SECTIONS
   /*--------------------------------------------------------------------*/
 
   /* Begining of code and text segment */
-  . = 0x00000000;
+  . = 0x00002000;
   _ftext = .;
   PROVIDE( eprol = . );
 
@@ -56,18 +56,6 @@ SECTIONS
     *(.gnu.linkonce.d.*)
   }
 
-  /* lit4: Single precision floating point constants created by gas */
-  .lit4 : 
-  {
-    *(.lit4)
-  }
-
-  /* lit8: Double precision floating point constants created by gas */
-  .lit8 : 
-  {
-    *(.lit8)
-  }
-
   /* End of initialized data segment */
   . = ALIGN(4);
   PROVIDE( edata = . );
@@ -83,14 +71,6 @@ SECTIONS
 
   /* sbss: Uninitialized writeable small data section */
   . = .;
-  _sbss_start = .;
-  .sbss : 
-  {
-    *(.sbss)
-    *(.sbss.*)
-    *(.gnu.linkonce.sb.*)
-    *(.scommon)
-  }
 
   /* bss: Uninitialized writeable data section */
   . = .;
diff --git a/pk/riscv-opc.h b/pk/riscv-opc.h
index 276d3fb..0bab6c4 100644
--- a/pk/riscv-opc.h
+++ b/pk/riscv-opc.h
@@ -124,13 +124,13 @@
 #define MATCH_VSSEGSTB 0x80f
 #define  MASK_VSSEGSTB 0xfff
 #define MATCH_MFTX_D 0x1c0d3
-#define  MASK_MFTX_D 0x7c1ffff
+#define  MASK_MFTX_D 0x3fffff
 #define MATCH_DIV 0x633
 #define  MASK_DIV 0x1ffff
 #define MATCH_C_LD 0x9
 #define  MASK_C_LD 0x1f
 #define MATCH_MFTX_S 0x1c053
-#define  MASK_MFTX_S 0x7c1ffff
+#define  MASK_MFTX_S 0x3fffff
 #define MATCH_VSSEGSTH 0x88f
 #define  MASK_VSSEGSTH 0xfff
 #define MATCH_VVCFGIVL 0xf3
@@ -154,7 +154,7 @@
 #define MATCH_VSB 0xf
 #define  MASK_VSB 0x3fffff
 #define MATCH_MFFSR 0x1d053
-#define  MASK_MFFSR 0x7ffffff
+#define  MASK_MFFSR 0x3fffff
 #define MATCH_FDIV_S 0x3053
 #define  MASK_FDIV_S 0x1f1ff
 #define MATCH_VLSTBU 0x120b
diff --git a/pk/riscv-pk.S b/pk/riscv-pk.S
index 6b91787..a27df82 100644
--- a/pk/riscv-pk.S
+++ b/pk/riscv-pk.S
@@ -2,37 +2,33 @@
 #include "pk.h"
 
 .section .text,"ax",@progbits
-.globl __start
-.ent __start
-__start:
+.globl _start
+.ent _start
+_start:
 
-  lui $sp, %hi(stack_top)
-  add $sp, $sp, %lo(stack_top)
+  lui sp, %hi(stack_top)
+  add sp, sp, %lo(stack_top)
 
-  lui $t0, %hi(trap_entry)
-  add $t0, $t0, %lo(trap_entry)
-  mtpcr $t0, ASM_CR(PCR_EVEC)
+  lui t0, %hi(trap_entry)
+  add t0, t0, %lo(trap_entry)
+  mtpcr t0, ASM_CR(PCR_EVEC)
 
-  mtpcr $x0, ASM_CR(PCR_COUNT)
-  li    $t0, TIMER_PERIOD
-  mtpcr $t0, ASM_CR(PCR_COMPARE)
-
-  li $t0, SR_S | SR_PS | SR_ET | SR_EC | SR_SX
-  or $t1, $t0, SR_EF | SR_EV
-  mtpcr $t1, ASM_CR(PCR_SR)
-  mfpcr $t1, ASM_CR(PCR_SR)
-  mtpcr $t0, ASM_CR(PCR_SR)
+  li t0, SR_S | SR_PS | SR_ET | SR_EC | SR_SX
+  or t1, t0, SR_EF | SR_EV
+  mtpcr t1, ASM_CR(PCR_SR)
+  mfpcr t1, ASM_CR(PCR_SR)
+  mtpcr t0, ASM_CR(PCR_SR)
   
-  and $t2, $t1, SR_EF
-  lui $t0, %hi(have_fp)
-  sw  $t2, %lo(have_fp)($t0)
+  and t2, t1, SR_EF
+  lui t0, %hi(have_fp)
+  sw  t2, %lo(have_fp)(t0)
   
-  and $t2, $t1, SR_EV
-  lui $t0, %hi(have_vector)
-  sw  $t2, %lo(have_vector)($t0)
+  and t2, t1, SR_EV
+  lui t0, %hi(have_vector)
+  sw  t2, %lo(have_vector)(t0)
 
-  lui $t0, %hi(boot)
-  jalr.j $t0, %lo(boot)
+  lui t0, %hi(boot)
+  jalr.j t0, %lo(boot)
   #j boot
 
-.end __start
+.end _start
diff --git a/pk/syscall.c b/pk/syscall.c
index 85c853b..f4c4f92 100644
--- a/pk/syscall.c
+++ b/pk/syscall.c
@@ -95,7 +95,7 @@ sysret_t sys_unlink(const char* name, size_t len)
 
 sysret_t sys_brk(size_t pos)
 {
-  if(pos > (mfpcr(PCR_MEMSIZE) << MEMSIZE_SHIFT))
+  if(pos / (1024 * 1024) >= mem_mb)
     return (sysret_t){-1, ENOMEM};
   return (sysret_t){0,0};
 }