diff --git a/.gitignore b/.gitignore
index 6b63016..9c95afb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,3 +4,5 @@
 /printstack
 /env
 /hexdump
+/prtest
+*.o
diff --git a/Makefile b/Makefile
index 7808680..b345799 100644
--- a/Makefile
+++ b/Makefile
@@ -9,11 +9,13 @@ all: true false cat env hexdump
 #all: echo
 
 %: %.o
-	$(LD) -o $@ $<
+	$(LD) -o $@ $(filter %.o, $^)
 
 %.o: %.s
 	$(AS) -o $@ $<
 
+prtest: prtest.o lib/printregs.o lib/hex.o
+
 .PHONY: test
 test:
 	@BIN=. test/true.sh
diff --git a/lib/hex.s b/lib/hex.s
new file mode 100644
index 0000000..28bd8a3
--- /dev/null
+++ b/lib/hex.s
@@ -0,0 +1,53 @@
+.global u64hex
+.global u32hex
+.global u8hex
+
+.macro hexnibble src, shift, dest
+    slli t1, \src, 64-\shift-4 # put high nibble of s7 in t1
+    srli t1, t1, 64-4
+    addi t2, t1, 0x30 # convert to decimal digit
+    bgt t5, t1, 0f # if digit >= 10, switch to alpha
+    addi t2, t1, 0x61-10
+0:
+    # copy digit to writebuf
+    sb t2, \dest
+.endm
+
+.macro hexbyte src, shift, dest
+    hexnibble \src, (\shift+4), \dest
+    hexnibble \src, \shift, 1+\dest
+.endm
+
+# arguments:
+# a0 - buffer (8, 16 bytes)
+# a1 - int (32, 64 bits)
+#
+# clobbers: t1, t2, t5
+# leaves a0 and a1 unchanged
+
+u64hex:
+    li t5, 10
+    hexbyte a1, 56, 0(a0)
+    hexbyte a1, 48, 2(a0)
+    hexbyte a1, 40, 4(a0)
+    hexbyte a1, 32, 6(a0)
+    hexbyte a1, 24, 8(a0)
+    hexbyte a1, 16, 10(a0)
+    hexbyte a1,  8, 12(a0)
+    hexbyte a1,  0, 14(a0)
+    ret
+
+u32hex:
+    li t5, 10
+    hexbyte a1, 24, 0(a0)
+    hexbyte a1, 16, 2(a0)
+    hexbyte a1, 8, 4(a0)
+    hexbyte a1, 0, 6(a0)
+    ret
+
+u8hex:
+    li t5, 10
+    hexbyte s7, 0, 6(a0)
+    ret
+    
+
diff --git a/lib/printregs.s b/lib/printregs.s
new file mode 100644
index 0000000..7cbc115
--- /dev/null
+++ b/lib/printregs.s
@@ -0,0 +1,207 @@
+.global printregs
+.extern u64hex
+
+.option rvc
+.option norelax # don't depend on gp being set correctly
+
+.data
+
+regmsg:
+.ascii " x1/ra=0x................   x5/t0=0x................   x8/s0=0x................\n"
+.ascii " x2/sp=0x................   x6/t1=0x................   x9/s1=0x................\n"
+.ascii " x3/gp=0x................   x7/t2=0x................\n"
+.ascii " x4/tp=0x................                             x18/s2=0x................\n"
+.ascii "                           x14/a4=0x................  x19/s3=0x................\n"
+.ascii "x10/a0=0x................  x15/a5=0x................  x20/s4=0x................\n"
+.ascii "x11/a1=0x................  x16/a6=0x................  x21/s5=0x................\n"
+.ascii "x12/a2=0x................  x17/a7=0x................\n"
+.ascii "x13/a3=0x................                             x28/t3=0x................\n"
+.ascii "                          x25/ s9=0x................  x29/t4=0x................\n"
+.ascii "x22/s6=0x................ x26/s10=0x................  x30/t5=0x................\n"
+.ascii "x23/s7=0x................ x27/s11=0x................  x31/t6=0x................\n"
+.ascii "x24/s8=0x................\n"
+.equ regmsg_size, (.) - regmsg
+
+#  x1 ra      x5 t0    x8 s0/fp
+#  x2 sp      x6 t1    x9 s1
+#  x3 gp      x7 t2
+#  x4 tp               x18 s2
+#             x14 a4   x19 s3
+#  x10 a0     x15 a5   x20 s4
+#  x11 a1     x16 a6   x21 s5
+#  x12 a2     x17 a7
+#  x13 a3              x28 t3
+#            x25 s9    x29 t4
+#  x22 s6    x26 s10   x30 t5
+#  x23 s7    x27 s11   x31 t6
+#  x24 s8
+#
+
+
+#  x1 ra     
+#  x2 sp      x5 t0    
+#  x3 gp      x6 t1    x8 s0/fp
+#  x4 tp      x7 t2    x9 s1
+#                               
+#  x10 a0     x14 a4   x18 s2
+#  x11 a1     x15 a5   x19 s3
+#  x12 a2     x16 a6   x20 s4
+#  x13 a3     x17 a7   
+#                      x28 t3
+#  x21 s5    x25 s9    x29 t4
+#  x22 s6    x26 s10   x30 t5
+#  x23 s7    x27 s11   x31 t6
+#  x24 s8    
+
+.text
+
+printregs:
+    # this routine is meant for debugging,
+    # so we treat all registers as callee-save
+
+    # TODO: consider saving to globals instead of the stack
+
+    # huh. it seems impossible to do anything useful
+    # with atomics without using registers
+    #
+    #    li           t0, 1        # Initialize swap value.
+    #  0:lw           t1, (a0)     # Check if lock is held.
+    #    bnez         t1, again    # Retry if held.
+    #    amoswap.w.aq t1, t0, (a0) # Attempt to acquire lock.
+    #    bnez         t1, 0b       # Retry if held.
+
+    # save regs to stack
+    sd sp, -8(sp)
+    addi sp, sp, -8*7
+    sd a0, 0(sp)
+    sd a1, 8(sp)
+    sd t1, 16(sp)
+    sd t2, 24(sp)
+    sd t5, 32(sp)
+    sd ra, 40(sp)
+
+    # copy string to stack?
+
+    # write registers to string
+    la a0, regmsg+9
+    ld a1, 40(sp) # x1 / ra
+    call u64hex
+    addi a0, a0, 16+11
+    mv a1, x5 # t0
+    call u64hex
+    addi a0, a0, 16+11
+    mv a1, x8 # s0
+    call u64hex
+
+    addi a0, a0, 16+10
+    ld a1, 48(sp) # x2/sp
+    call u64hex
+    addi a0, a0, 16+11
+    ld a1, 16(sp) # x6/t1
+    call u64hex
+    addi a0, a0, 16+11
+    mv a1, x9 # s1
+    call u64hex
+
+    addi a0, a0, 16+10
+    mv a1, x3 # gp
+    call u64hex
+    addi a0, a0, 16+11
+    ld a1, 24(sp) # x7/t2
+    call u64hex
+
+    addi a0, a0, 16+10
+    mv a1, x4 # tp
+    call u64hex
+    addi a0, a0, 16+11 + 16+11
+    mv a1, x18 # s2
+    call u64hex
+
+    addi a0, a0, 16+10 + 16+11
+    mv a1, x14 # a4
+    call u64hex
+    addi a0, a0, 16+11
+    mv a1, x19 # s3
+    call u64hex
+
+    addi a0, a0, 16+10
+    ld a1, 0(sp) # x10/a0
+    call u64hex
+    addi a0, a0, 16+11
+    mv a1, x15 # a5
+    call u64hex
+    addi a0, a0, 16+11
+    mv a1, x20 # s4
+    call u64hex
+
+    addi a0, a0, 16+10
+    ld a1, 8(sp) # a1
+    call u64hex
+    addi a0, a0, 16+11
+    mv a1, x16 # a6
+    call u64hex
+    addi a0, a0, 16+11
+    mv a1, x21 # s5
+    call u64hex
+
+    addi a0, a0, 16+10
+    mv a1, x12 # a2
+    call u64hex
+    addi a0, a0, 16+11
+    mv a1, x17 # a7
+    call u64hex
+
+    addi a0, a0, 16+10
+    mv a1, x13 # a3
+    call u64hex
+    addi a0, a0, 16+11 + 16+11
+    mv a1, x28 # t3
+    call u64hex
+
+    addi a0, a0, 16+10 + 16+11
+    mv a1, x25 # s9
+    call u64hex
+    addi a0, a0, 16+11
+    mv a1, x29 # t4
+    call u64hex
+
+    addi a0, a0, 16+10
+    mv a1, x22 # s6
+    call u64hex
+    addi a0, a0, 16+11
+    mv a1, x26 # s10
+    call u64hex
+    addi a0, a0, 16+11
+    ld a1, 32(sp) # x30 / t5
+    call u64hex
+
+    addi a0, a0, 16+10
+    mv a1, x23 # s7
+    call u64hex
+    addi a0, a0, 16+11
+    mv a1, x27 # s11
+    call u64hex
+    addi a0, a0, 16+11
+    mv a1, x31 # t6
+    call u64hex
+
+    addi a0, a0, 16+10
+    mv a1, x24 # s8
+    call u64hex
+
+    # print string
+    li a7, 64 # sys_write
+    li a0, 1 # stdout
+    la a1, regmsg
+    li a2, regmsg_size
+    ecall
+    
+    # restore saved registers
+    ld a0, 0(sp)
+    ld a1, 8(sp)
+    ld t1, 16(sp)
+    ld t2, 24(sp)
+    ld t5, 32(sp)
+    ld ra, 40(sp)
+    ld sp, 48(sp)
+    ret
diff --git a/prtest.s b/prtest.s
new file mode 100644
index 0000000..7b93cb9
--- /dev/null
+++ b/prtest.s
@@ -0,0 +1,39 @@
+
+.globl _start
+.extern printregs
+
+.text
+
+_start:
+    li x5, 5
+    li x6, 6
+    li x7, 7
+    li x8, 8
+    li x9, 9
+    li x10, 10
+    li x11, 11
+    li x12, 12
+    li x13, 13
+    li x14, 14
+    li x15, 15
+    li x16, 16
+    li x17, 17
+    li x18, 18
+    li x19, 19
+    li x20, 20
+    li x21, 21
+    li x22, 22
+    li x23, 23
+    li x24, 24
+    li x25, 25
+    li x26, 26
+    li x27, 27
+    li x28, 28
+    li x29, 29
+    li x30, 30
+    li x31, 31
+    call printregs
+    li a7, 93 # sys_exit
+    li a0, 0
+    ecall
+