Kernel: Fix memset() on x86_64

Previously memset() only set half of the bytes to the requested value.

AK/Types.h

@@ -65,14 +65,24 @@ namespace std {
 using nullptr_t = decltype(nullptr);
 }
 
-static constexpr u32 explode_byte(u8 b)
+static constexpr FlatPtr explode_byte(u8 b)
 {
-    return b << 24 | b << 16 | b << 8 | b;
+#if ARCH(I386)
+    return (u32)b << 24 | (u32)b << 16 | (u32)b << 8 | (u32)b;
+#else
+    return (u64)b << 56 | (u64)b << 48 | (u64)b << 40 | (u64)b << 32 | (u64)b << 24 | (u64)b << 16 | (u64)b << 8 | (u64)b;
+#endif
 }
 
+#if ARCH(I386)
 static_assert(explode_byte(0xff) == 0xffffffff);
 static_assert(explode_byte(0x80) == 0x80808080);
 static_assert(explode_byte(0x7f) == 0x7f7f7f7f);
+#else
+static_assert(explode_byte(0xff) == 0xffffffffffffffff);
+static_assert(explode_byte(0x80) == 0x8080808080808080);
+static_assert(explode_byte(0x7f) == 0x7f7f7f7f7f7f7f7f);
+#endif
 static_assert(explode_byte(0) == 0);
 
 constexpr size_t align_up_to(const size_t value, const size_t alignment)

Kernel/Arch/x86/common/Interrupts.cpp

@@ -356,12 +356,12 @@ void page_fault_handler(TrapFrame* trap)
             regs.exception_code & PageFaultFlags::InstructionFetch ? "instruction fetch / " : "",
             regs.exception_code & PageFaultFlags::Write ? "write to" : "read from",
             VirtualAddress(fault_address));
-        u32 malloc_scrub_pattern = explode_byte(MALLOC_SCRUB_BYTE);
-        u32 free_scrub_pattern = explode_byte(FREE_SCRUB_BYTE);
-        u32 kmalloc_scrub_pattern = explode_byte(KMALLOC_SCRUB_BYTE);
-        u32 kfree_scrub_pattern = explode_byte(KFREE_SCRUB_BYTE);
-        u32 slab_alloc_scrub_pattern = explode_byte(SLAB_ALLOC_SCRUB_BYTE);
-        u32 slab_dealloc_scrub_pattern = explode_byte(SLAB_DEALLOC_SCRUB_BYTE);
+        FlatPtr malloc_scrub_pattern = explode_byte(MALLOC_SCRUB_BYTE);
+        FlatPtr free_scrub_pattern = explode_byte(FREE_SCRUB_BYTE);
+        FlatPtr kmalloc_scrub_pattern = explode_byte(KMALLOC_SCRUB_BYTE);
+        FlatPtr kfree_scrub_pattern = explode_byte(KFREE_SCRUB_BYTE);
+        FlatPtr slab_alloc_scrub_pattern = explode_byte(SLAB_ALLOC_SCRUB_BYTE);
+        FlatPtr slab_dealloc_scrub_pattern = explode_byte(SLAB_DEALLOC_SCRUB_BYTE);
         if ((fault_address & 0xffff0000) == (malloc_scrub_pattern & 0xffff0000)) {
             dbgln("Note: Address {} looks like it may be uninitialized malloc() memory", VirtualAddress(fault_address));
         } else if ((fault_address & 0xffff0000) == (free_scrub_pattern & 0xffff0000)) {