luna, kernel: Replace some uses of char by truly 1-byte wide types

(avoid division and modulo, division is slow)
Fortunately, GCC will optimize divisions by powers of two to simple bitwise shifts :)

kernel/src/arch/Timer.cpp

@@ -2,8 +2,10 @@
 #include "Log.h"
 #include "arch/Serial.h"
 #include "boot/bootboot.h"
+#include <luna/TypeTraits.h>
 
-// FIXME: Storing these values as unsigned integers doesn't allow for pre-epoch times.
+// NOTE: Storing these values as unsigned integers doesn't allow for pre-epoch times.
+// We are in 2023 anyway, not sure why anybody would want to set their computer's time to 1945.
 static u64 timer_ticks = 0;
 static u64 boot_timestamp;
 
@@ -134,8 +136,9 @@ namespace Timer
     }
 }
 
+static_assert(IsPowerOfTwo<usize, ARCH_TIMER_FREQ>, "ARCH_TIMER_FREQ must be a power of two");
+
 bool should_invoke_scheduler()
 {
-    // FIXME: Modulo is SLOW. We're calling this every tick.
     return (timer_ticks % ARCH_TIMER_FREQ) == 0;
 }

kernel/src/arch/x86_64/Timer.h

@@ -1,4 +1,4 @@
 #pragma once
 #include <luna/Types.h>
 
-const usize ARCH_TIMER_FREQ = 5;
+const usize ARCH_TIMER_FREQ = 4;

kernel/src/memory/MemoryManager.cpp

@@ -433,7 +433,7 @@ namespace MemoryManager
         uintptr_t user_ptr = (uintptr_t)user;
         uintptr_t user_page = align_down<ARCH_PAGE_SIZE>(user_ptr);
 
-        const char* kernel_ptr = (const char*)kernel;
+        const u8* kernel_ptr = (const u8*)kernel;
 
         // Userspace pointer not aligned on page boundary
         if (user_ptr != user_page)
@@ -449,7 +449,7 @@ namespace MemoryManager
                 if (!validate_user_writable_page(user_ptr)) return false;
             }
 
-            *(char*)user_ptr = *kernel_ptr++;
+            *(u8*)user_ptr = *kernel_ptr++;
             user_ptr++;
         }
 
@@ -461,7 +461,7 @@ namespace MemoryManager
         uintptr_t user_ptr = (uintptr_t)user;
         uintptr_t user_page = align_down<ARCH_PAGE_SIZE>(user_ptr);
 
-        char* kernel_ptr = (char*)kernel;
+        u8* kernel_ptr = (u8*)kernel;
 
         // Userspace pointer not aligned on page boundary
         if (user_ptr != user_page)
@@ -477,7 +477,7 @@ namespace MemoryManager
                 if (!validate_user_readable_page(user_ptr)) return false;
             }
 
-            *kernel_ptr++ = *(const char*)user_ptr;
+            *kernel_ptr++ = *(const u8*)user_ptr;
             user_ptr++;
         }
 

luna/include/luna/Alignment.h

@@ -49,5 +49,5 @@ static_assert(get_blocks_from_size(0, 256) == 0);
 // arithmetic.
 template <typename T, typename Offset> constexpr T* offset_ptr(T* ptr, Offset offset)
 {
-    return (T*)((char*)ptr + offset);
+    return (T*)((u8*)ptr + offset);
 }

luna/src/Heap.cpp

@@ -27,8 +27,8 @@ static constexpr int BLOCK_END_MEM = 1 << 2;
 static constexpr usize BLOCK_MAGIC = 0x6d616c6c6f63210a; // echo 'malloc!' | hexdump -C (includes a newline)
 static constexpr usize BLOCK_DEAD = 0xdeaddeaddeaddead;
 
-static constexpr u8 KMALLOC_SCRUB_BYTE = 0xac;
-static constexpr u8 KFREE_SCRUB_BYTE = 0xde;
+static constexpr u8 MALLOC_SCRUB_BYTE = 0xac;
+static constexpr u8 FREE_SCRUB_BYTE = 0xde;
 
 static constexpr usize MINIMUM_PAGES_PER_ALLOCATION = 4;
 
@@ -221,7 +221,7 @@ Result<void*> malloc_impl(usize size, bool should_scrub)
     current->req_size = size;
     current->status |= BLOCK_USED;
 
-    if (should_scrub) { memset(get_pointer_from_heap_block(current), KMALLOC_SCRUB_BYTE, size); }
+    if (should_scrub) { memset(get_pointer_from_heap_block(current), MALLOC_SCRUB_BYTE, size); }
 
     return get_pointer_from_heap_block(current);
 }
@@ -237,7 +237,7 @@ Result<void> free_impl(void* ptr)
     {
         if (block->magic == BLOCK_DEAD) { dbgln("ERROR: Attempt to free memory at %p, which was already freed", ptr); }
         else
-            dbgln("ERROR: Attempt to free memory at %p, which wasn't allocated with kmalloc", ptr);
+            dbgln("ERROR: Attempt to free memory at %p, which wasn't allocated with malloc", ptr);
 
         return err(EFAULT);
     }
@@ -250,7 +250,7 @@ Result<void> free_impl(void* ptr)
     else
         block->status &= ~BLOCK_USED;
 
-    memset(ptr, KFREE_SCRUB_BYTE, block->req_size);
+    memset(ptr, FREE_SCRUB_BYTE, block->req_size);
 
     auto maybe_next = heap.next(block);
     if (maybe_next.has_value() && is_block_free(maybe_next.value()))
@@ -295,7 +295,7 @@ Result<void*> realloc_impl(void* ptr, usize size)
             dbgln("ERROR: Attempt to realloc memory at %p, which was already freed", ptr);
         }
         else
-            dbgln("ERROR: Attempt to realloc memory at %p, which wasn't allocated with kmalloc", ptr);
+            dbgln("ERROR: Attempt to realloc memory at %p, which wasn't allocated with malloc", ptr);
 
         return err(EFAULT);
     }
@@ -311,7 +311,16 @@ Result<void*> realloc_impl(void* ptr, usize size)
     if (block->full_size >= size)
     {
         // This block is already large enough!
-        // FIXME: Scrub this if necessary.
+        if (size > block->req_size)
+        {
+            // If the new size is larger, scrub the newly allocated space.
+            memset(offset_ptr(ptr, block->req_size), MALLOC_SCRUB_BYTE, size - block->req_size);
+        }
+        else if (size < block->req_size)
+        {
+            // If the new size is smaller, scrub the removed space as if it was freed.
+            memset(offset_ptr(ptr, size), FREE_SCRUB_BYTE, block->req_size - size);
+        }
         block->req_size = size;
         return ptr;
     }
@@ -322,7 +331,7 @@ Result<void*> realloc_impl(void* ptr, usize size)
     memcpy(new_ptr, ptr, old_size > size ? size : old_size);
     TRY(free_impl(ptr));
 
-    if (old_size < size) { memset(offset_ptr(new_ptr, old_size), KMALLOC_SCRUB_BYTE, size - old_size); }
+    if (old_size < size) { memset(offset_ptr(new_ptr, old_size), MALLOC_SCRUB_BYTE, size - old_size); }
 
     return new_ptr;
 }