From 2490a4e4dfb3fd0ea334ab510c10aefb45a5f02b Mon Sep 17 00:00:00 2001
From: Imbus <>
Date: Thu, 26 Jun 2025 02:57:34 +0200
Subject: [PATCH] Register clearing as a separate assembly routine in entry.S

---
 entry.S | 73 +++++++++++++++++++++++++++++++++------------------------
 1 file changed, 42 insertions(+), 31 deletions(-)

diff --git a/entry.S b/entry.S
index 377f81f..f32657c 100644
--- a/entry.S
+++ b/entry.S
@@ -1,10 +1,46 @@
 .section .text
 .globl _start
 _start:
-    li x1, 0x0
-    li x2, 0x0
-    li x3, 0x0
-    li x4, 0x0
+    # Both call and j will work here, but since ra will be cleared,
+    # we will need a jump instruction back (from _clear) to continue.
+    call _clear
+
+continue:
+    li t0, 0x10000000    # UART base address
+    li t1, 'E'           # Character to print
+    sb t1, 0(t0)
+    li t1, 'n'
+    sb t1, 0(t0)
+    li t1, 't'
+    sb t1, 0(t0)
+    li t1, 'r'
+    sb t1, 0(t0)
+    li t1, 'y'
+    sb t1, 0(t0)
+    li t1, '\n'
+    sb t1, 0(t0)
+
+    # Set up a stack for C.
+    la sp, stack0
+    li a0, 1024*4       # a0 = 4096
+    csrr a1, mhartid    # a1 = hart id
+    addi a1, a1, 1      # hartid + 1
+    mul a0, a0, a1      # a0 *= hartid+1
+    add sp, sp, a0      # sp += a0
+
+    # Jump to start() in start.c
+    call start
+
+1:
+    j 1b                 # Infinite loop
+
+.section .text
+.globl _clear
+_clear:
+    li x1, 0x0 # ra: Return address
+    li x2, 0x0 # sp: Stack points
+    li x3, 0x0 # gp: Global pointer
+    li x4, 0x0 # tp: Thread pointer
     li x5, 0x0
     li x6, 0x0
     li x7, 0x0
@@ -33,30 +69,5 @@ _start:
     li x30, 0x0
     li x31, 0x0
 
-    li t0, 0x10000000    # UART base address
-    li t1, 'E'           # Character to print
-    sb t1, 0(t0)
-    li t1, 'n'
-    sb t1, 0(t0)
-    li t1, 't'
-    sb t1, 0(t0)
-    li t1, 'r'
-    sb t1, 0(t0)
-    li t1, 'y'
-    sb t1, 0(t0)
-    li t1, '\n'
-    sb t1, 0(t0)
-
-    # Set up a stack for C.
-    la sp, stack0
-    li a0, 1024*4       # a0 = 4096
-    csrr a1, mhartid    # a1 = hart id
-    addi a1, a1, 1      # hartid + 1
-    mul a0, a0, a1      # a0 *= hartid+1
-    add sp, sp, a0      # sp += a0
-
-    # Jump to start() in start.c
-    call start
-
-1:
-    j 1b                 # Infinite loop
+    # ret wont work here since we cleared x1
+    j continue