From 08a9d991eb38c7f9c8eef7462a0456230a0c556b Mon Sep 17 00:00:00 2001
From: Rohan Bafna <rbafna3@gatech.edu>
Date: Sun, 12 Jan 2025 16:54:42 -0500
Subject: [PATCH] Add sentinel ebp values

---
 kernel/src/asm/entry.S      | 3 +++
 kernel/src/asm/entryother.S | 3 +++
 kernel/src/asm/trapasm.S    | 3 +++
 kernel/src/proc.c           | 2 ++
 4 files changed, 11 insertions(+)

diff --git a/kernel/src/asm/entry.S b/kernel/src/asm/entry.S
index b3f1afc..eceb260 100644
--- a/kernel/src/asm/entry.S
+++ b/kernel/src/asm/entry.S
@@ -55,6 +55,9 @@ entry:
   orl     $(CR0_PG|CR0_WP), %eax
   movl    %eax, %cr0
 
+  # LAB 1: Set sentinel value of %ebp
+  movl    $0xF00, %ebp
+
   # Set up the stack pointer.
   movl $(stack + KSTACKSIZE), %esp
 
diff --git a/kernel/src/asm/entryother.S b/kernel/src/asm/entryother.S
index 757e7f9..0d36df6 100644
--- a/kernel/src/asm/entryother.S
+++ b/kernel/src/asm/entryother.S
@@ -67,6 +67,9 @@ start32:
   orl     $(CR0_PE|CR0_PG|CR0_WP), %eax
   movl    %eax, %cr0
 
+  # LAB 1: Set sentinel value of %ebp
+  movl    $0xF00, %ebp
+
   # Switch to the stack allocated by startothers()
   movl    (start-4), %esp
   # Call mpenter()
diff --git a/kernel/src/asm/trapasm.S b/kernel/src/asm/trapasm.S
index da8aefc..c0d061a 100644
--- a/kernel/src/asm/trapasm.S
+++ b/kernel/src/asm/trapasm.S
@@ -15,6 +15,9 @@ alltraps:
   movw %ax, %ds
   movw %ax, %es
 
+  # LAB 1: Set sentinel value of %ebp
+  movl $0xF00, %ebp
+
   # Call trap(tf), where tf=%esp
   pushl %esp
   call trap
diff --git a/kernel/src/proc.c b/kernel/src/proc.c
index c140f40..64d3fdf 100644
--- a/kernel/src/proc.c
+++ b/kernel/src/proc.c
@@ -113,6 +113,8 @@ found:
   p->context = (struct context*)sp;
   memset(p->context, 0, sizeof *p->context);
   p->context->eip = (uint)forkret;
+  // LAB 1: Set sentinel value of %ebp
+  p->context->ebp = 0xF00;
 
   return p;
 }
-- 
2.47.3