From 9072c2a277c0da298b977cf4fb3dbebb5481abd0 Mon Sep 17 00:00:00 2001
From: Fabian Imhof <fabian.imhof@ost.ch>
Date: Sun, 1 Dec 2024 13:34:46 +0000
Subject: implement clear_memory_block_header

---
 .../arch/memory/heap/linked_list_allocator.hpp     |  3 +++
 arch/x86_64/src/kernel/main.cpp                    |  8 +++++---
 .../src/memory/heap/linked_list_allocator.cpp      | 22 +++++++++++++++-------
 3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/arch/x86_64/include/arch/memory/heap/linked_list_allocator.hpp b/arch/x86_64/include/arch/memory/heap/linked_list_allocator.hpp
index 236d366..7432561 100644
--- a/arch/x86_64/include/arch/memory/heap/linked_list_allocator.hpp
+++ b/arch/x86_64/include/arch/memory/heap/linked_list_allocator.hpp
@@ -59,6 +59,9 @@ namespace teachos::arch::memory::heap
     auto coalesce_free_memory_block(memory_block *& previous_block, memory_block *& current_block, void * pointer,
                                     std::size_t size) -> void;
 
+    // We cannot call delete, because it causes "undefined reference to `sbrk`".
+    auto clear_memory_block_header(void * pointer) -> void;
+
     std::size_t heap_start;  ///< Start of the allocatable heap area
     std::size_t heap_end;    ///< End of the allocatable heap area
     memory_block * first;    ///< First free entry in our memory
diff --git a/arch/x86_64/src/kernel/main.cpp b/arch/x86_64/src/kernel/main.cpp
index ea18232..a4f138c 100644
--- a/arch/x86_64/src/kernel/main.cpp
+++ b/arch/x86_64/src/kernel/main.cpp
@@ -26,8 +26,8 @@ namespace teachos::arch::kernel
                                                        memory::heap::HEAP_START + memory::heap::HEAP_SIZE};
     auto test = heap_allocator.allocate(1024);
     auto test2 = new (test) memory::multiboot::memory_information{};
-    test = static_cast<void *>(static_cast<memory::multiboot::memory_information *>(test) + 1);
-    auto test3 = new (test) memory::multiboot::memory_information{};
+    auto test3 = new (static_cast<void *>(static_cast<memory::multiboot::memory_information *>(test) + 1))
+        memory::multiboot::memory_information{};
     auto test4 = *test2;
     auto test5 = *test3;
     test4.kernel_end = 5000;
@@ -39,6 +39,8 @@ namespace teachos::arch::kernel
     {
       video::vga::text::write("Kernel remapping successfull", video::vga::text::common_attributes::green_on_black);
     }
+
+    heap_allocator.deallocate(test, 1024);
   }
 
   auto main() -> void
@@ -50,6 +52,6 @@ namespace teachos::arch::kernel
     memory::initialize_memory_management();
 
     // stack_overflow_test(0);
-    heap_test();
+    // heap_test();
   }
 }  // namespace teachos::arch::kernel
diff --git a/arch/x86_64/src/memory/heap/linked_list_allocator.cpp b/arch/x86_64/src/memory/heap/linked_list_allocator.cpp
index 63a762e..07d7e5e 100644
--- a/arch/x86_64/src/memory/heap/linked_list_allocator.cpp
+++ b/arch/x86_64/src/memory/heap/linked_list_allocator.cpp
@@ -3,6 +3,8 @@
 #include "arch/exception_handling/assert.hpp"
 #include "arch/exception_handling/panic.hpp"
 
+#include <string.h>
+
 #include <algorithm>
 
 namespace teachos::arch::memory::heap
@@ -14,7 +16,7 @@ namespace teachos::arch::memory::heap
   {
     auto const heap_size = heap_end - heap_start;
     exception_handling::assert(
-        heap_size < min_allocatable_size(),
+        heap_size > min_allocatable_size(),
         "[Linked List Allocator] Total heap size can not be smaller than minimum of 16 bytes to hold "
         "atleast one memory hole entry");
     first = new (reinterpret_cast<void *>(heap_start)) memory_block(heap_size, nullptr);
@@ -22,7 +24,7 @@ namespace teachos::arch::memory::heap
 
   auto linked_list_allocator::allocate(std::size_t size) -> void *
   {
-    exception_handling::assert(size < min_allocatable_size(),
+    exception_handling::assert(size > min_allocatable_size(),
                                "[Linked List Allocator] Allocated memory cannot be smaller than 16 bytes");
 
     auto & previous = first;
@@ -34,7 +36,8 @@ namespace teachos::arch::memory::heap
       {
         return split_free_memory_block(current, size);
       }
-      else if (current->size >= size)
+
+      if (current->size >= size)
       {
         if (previous != current)
         {
@@ -42,10 +45,10 @@ namespace teachos::arch::memory::heap
         }
         else
         {
-          current = current->next;
+          first = current->next;
         }
 
-        delete current;
+        clear_memory_block_header(current);
         return static_cast<void *>(current);
       }
 
@@ -57,7 +60,7 @@ namespace teachos::arch::memory::heap
 
   auto linked_list_allocator::deallocate(void * pointer, std::size_t size) -> void
   {
-    exception_handling::assert(size < min_allocatable_size(),
+    exception_handling::assert(size > min_allocatable_size(),
                                "[Linked List Allocator] Allocated memory cannot be smaller than 16 bytes");
 
     auto const start_address = reinterpret_cast<std::size_t>(pointer);
@@ -118,7 +121,7 @@ namespace teachos::arch::memory::heap
       block_size += current_block->size;
       next_block = current_block->next;
 
-      delete current_block;
+      clear_memory_block_header(current_block);
     }
 
     // If the block we want to deallocate is behind another free block and we can therefore combine both into one.
@@ -137,4 +140,9 @@ namespace teachos::arch::memory::heap
     previous_block->next = new_block;
   }
 
+  auto linked_list_allocator::clear_memory_block_header(void * pointer) -> void
+  {
+    memset(pointer, 0, min_allocatable_size());
+  }
+
 }  // namespace teachos::arch::memory::heap
-- 
cgit v1.2.3