From 085857a900ce5a890ea06a35cd9f5e2aeea6d63c Mon Sep 17 00:00:00 2001
From: Mathieu Maret <mathieu.maret@gmail.com>
Date: Fri, 16 Nov 2018 14:47:21 +0100
Subject: [PATCH] Add backtrace function

---
 Makefile     |  6 ++++--
 core/stack.c | 28 ++++++++++++++++++++++++++++
 core/stack.h |  3 +++
 3 files changed, 35 insertions(+), 2 deletions(-)
 create mode 100644 core/stack.c
 create mode 100644 core/stack.h

diff --git a/Makefile b/Makefile
index c64f685..6eb59de 100644
--- a/Makefile
+++ b/Makefile
@@ -2,9 +2,11 @@
 CPPFLAGS = -MMD
 AS=nasm
 ASFLAGS += -f elf32
+#LDFLAGS += -m32 -nostdlib -mkernel -fno-stack-protector
 LDFLAGS += -m32 -nostdlib -static -fno-common -fno-use-cxa-atexit -fno-exceptions -fno-non-call-exceptions -fno-weak -fno-rtti -fno-stack-protector
 CFLAGS += -m32 -Wall -Wextra -Werror -ffreestanding  -fno-exceptions -fno-pie -fno-stack-protector
 CXXFLAGS += -m32 -Wall -Wextra -Werror -ffreestanding  -fno-exceptions -fno-rtti -fno-pie
+DEBUG_FLAGS += -g -Og -DDEBUG -fno-omit-frame-pointer
 
 SUBDIRS := core drivers tests
 
@@ -44,8 +46,8 @@ self_test: clean kernel
 test:kernel
 	qemu-system-x86_64 -kernel $<
 
-debug: CFLAGS += -g -Og
-debug: CXXFLAGS += -g -Og
+debug: CFLAGS += $(DEBUG_FLAGS)
+debug: CXXFLAGS += $(DEBUG_FLAGS)
 debug:kernel kernel.sym
 	qemu-system-x86_64 -s -S -kernel kernel&
 	gdb -s kernel.sym -ex "target remote localhost:1234"
diff --git a/core/stack.c b/core/stack.c
new file mode 100644
index 0000000..b6a79ab
--- /dev/null
+++ b/core/stack.c
@@ -0,0 +1,28 @@
+#include "stack.h"
+#include "vga.h"
+
+void printStackTrace(unsigned int maxFrames){
+#ifdef DEBUG
+	// Now on Stack:
+	// 	( potential second function argument )
+	//	first function argument (maxFrames)
+	//	return address from caller
+	//	EBP (Extended Base Pointer) of calling function
+	unsigned int * ebp = &maxFrames - 2;
+	for (unsigned int frame = 0 ; frame < maxFrames; frame ++){
+		unsigned int eip = ebp [1];
+		if (eip == 0){
+			// No caller on stack
+			break;
+		}
+		ebp = (unsigned int *)(ebp[0]);
+		//unsigned int * arguments = &ebp[2];
+		printf("    0x%x\n", eip);
+	}
+#else
+	printf("Must be compiled with -fno-omit-frame-pointer for full stack\n");
+	unsigned int * ebp = &maxFrames - 2;
+	unsigned int eip = ebp [1];
+	printf("Caller:    0x%x\n", eip);
+#endif
+}
diff --git a/core/stack.h b/core/stack.h
new file mode 100644
index 0000000..a0265cd
--- /dev/null
+++ b/core/stack.h
@@ -0,0 +1,3 @@
+#pragma once
+
+void printStackTrace(unsigned int maxFrame);