From 947f1fca89da7296d0e91353a8304e01d45654d1 Mon Sep 17 00:00:00 2001
From: Wesley Moore <wes@wezm.net>
Date: Mon, 10 Feb 2025 14:00:44 +1000
Subject: [PATCH] Attempt to print register values in regdump
---
calc.s | 63 ++++++++++++++++++++++++++++++++++++++++++----------------
hex.s | 8 ++++++--
2 files changed, 52 insertions(+), 19 deletions(-)
diff --git a/calc.s b/calc.s
index d1be333..22b58df 100644
--- a/calc.s
+++ b/calc.s
@@ -4,6 +4,8 @@
# Provide program starting address to linker
.global _start
+.extern tohex
+
/* newlib system calls */
.set SYSEXIT, 93
.set SYSWRITE, 64
@@ -54,7 +56,7 @@ end:
li a1, 1 # 1
li a2, 0x80000000 # 0.5
li a3, 1 # 1
- jal add64
+ # jal add64
#add t1, a0, 0 # copy a0 to t0 as end with overwrite it
jal regdump
@@ -83,11 +85,25 @@ add64:
# Print values of all registers (in hex)
# write syscall uses t0, a0, a1, a2
regdump:
- addi sp, sp, -16 # allocate stack space
- sw a0, 12(sp) # save contents of a0
- sw a1, 8(sp) # save contents of a0
- sw a2, 4(sp) # save contents of a0
- sw t0, 0(sp) # save contents of a0
+ # save all registers to preserve their state when entering the function
+ # except sp, which will be offset by -64
+ addi sp, sp, -64 # allocate stack space to stash all registers
+ sw x0, 0(sp)
+ sw x1, 4(sp)
+ sw x2, 8(sp)
+ sw x3, 12(sp)
+ sw x4, 16(sp)
+ sw x5, 20(sp)
+ sw x6, 24(sp)
+ sw x7, 28(sp)
+ sw x8, 32(sp)
+ sw x9, 36(sp)
+ sw x10, 40(sp)
+ sw x11, 44(sp)
+ sw x12, 48(sp)
+ sw x13, 52(sp)
+ sw x14, 56(sp)
+ sw x15, 60(sp)
li t0, SYSWRITE # "write" syscall
li a0, 1 # 1 = standard output (stdout)
@@ -107,32 +123,45 @@ regdump_loop:
# copy regname to buf
la a0, buf # load address of buf into a0 as dest
li a2, 2 # copy 2 bytes
-
- addi sp, sp, -4 # allocate stack space
- sw ra, 0(sp) # save contents of ra
+ addi sp, sp, -4 # allocate stack space
+ sw ra, 0(sp) # save contents of ra
jal memcpy
- lw ra, 0(sp) # save contents of ra
- addi sp, sp, 4 # deallocate stack space
- # append ': \n'
+ lw ra, 0(sp) # restore contents of ra
+ addi sp, sp, 4 # deallocate stack space
+ # append ': '
li t0, ':
sb t0, 0(a0)
li t0, 0x20
sb t0, 1(a0)
- li t0, '\n
- sb t0, 2(a0)
+ addi a0, a0, 2 # bump a0 address over ': ' text
+ mv a1, a0 # load address of output buffer to a1
+ slli a2, s0, 2 # calculate the offset of the register value relative to sp
+ add a2, a2, sp # a2 = sp + (s0 * 4)
+ lw a0, 0(a2) # load register value to format into a0
+ addi sp, sp, -8 # allocate stack space
+ sw a1, 4(sp) # save contents of a1
+ sw ra, 0(sp) # save contents of ra
+ jal tohex
+ lw ra, 0(sp) # restore contents of ra
+ lw a1, 4(sp) # restore contents of a1 (buffer)
+ addi sp, sp, 8 # deallocate stack space
+ li t0, '\n # append newline
+ sb t0, 8(a1)
- # print the register name
+ # print the register name and value
li t0, SYSWRITE # "write" syscall
li a0, 1 # 1 = standard output (stdout)
la a1, buf
- li a2, 5 # length of register name string
+ li a2, 4+8+1 # length of register name string:
+ # rr: 12345678\n
ecall # invoke syscall to print the string
addi s0, s0, 1
j regdump_loop
regdump_done:
- addi sp, sp, 16 # deallocate stack space
+ # TODO: Restore s0 & s1
+ addi sp, sp, 64 # deallocate stack space
ret
diff --git a/hex.s b/hex.s
index 034f72e..dc9c696 100644
--- a/hex.s
+++ b/hex.s
@@ -16,10 +16,12 @@ hexchars:
# return:
# none
tohex:
+ addi sp, sp, -20 # allocate stack space
+ sw s0, 12(sp) # save contents of s0
+ sw s1, 8(sp) # save contents of s1
li s0, 0 # set up loop variables
li s1, 4
addi a1, a1, 6 # offset output address to end chars
- addi sp, sp, -12 # allocate stack space
tohex_loop:
sw ra, 8(sp) # save contents of ra
sw a0, 4(sp) # save contents of ra
@@ -33,7 +35,9 @@ tohex_loop:
addi a1, a1, -2 # decrement output buffer address
addi s0, s0, 1 # increment loop counter
blt s0, s1, tohex_loop # TODO: we don't need the loop counter and output addr
- addi sp, sp, 12 # deallocate stack space
+ lw s0, 12(sp) # restore s0 & s1
+ lw s1, 8(sp)
+ addi sp, sp, 20 # deallocate stack space
ret
# Convert byte to ASCII hex