Use modern C++ attributes instead of __attribute__ voodoo.

This is quite nice, although I wish [[gnu::always_inline]] implied inline.
Also "gnu::" is kind of a wart, but whatcha gonna do.

34 files changed, 99 insertions, 124 deletions

diff --git a/AK/Compiler.h b/AK/Compiler.h
deleted file mode 100644
index 78e43498e7..0000000000
--- a/AK/Compiler.h
+++ /dev/null
@@ -1,11 +0,0 @@
-#pragma once
-
-#define PACKED __attribute__ ((packed))
-#define NORETURN __attribute__ ((noreturn))
-#define FLATTEN __attribute__ ((flatten))
-#undef ALWAYS_INLINE
-#define ALWAYS_INLINE inline __attribute__ ((always_inline))
-#define NEVER_INLINE __attribute__ ((noinline))
-#define MALLOC_ATTR __attribute__ ((malloc))
-#define PURE __attribute__ ((pure))
-#define WARN_UNUSED_RESULT __attribute__ ((warn_unused_result))
diff --git a/AK/Lock.h b/AK/Lock.h
index da5a2e1de9..d5ebaf6041 100644
--- a/AK/Lock.h
+++ b/AK/Lock.h
@@ -44,10 +44,10 @@ private:
 
 class Locker {
 public:
-    ALWAYS_INLINE explicit Locker(Lock& l) : m_lock(l) { lock(); }
-    ALWAYS_INLINE ~Locker() { unlock(); }
-    ALWAYS_INLINE void unlock() { m_lock.unlock(); }
-    ALWAYS_INLINE void lock() { m_lock.lock(); }
+    [[gnu::always_inline]] explicit Locker(Lock& l) : m_lock(l) { lock(); }
+    [[gnu::always_inline]] ~Locker() { unlock(); }
+    [[gnu::always_inline]] void unlock() { m_lock.unlock(); }
+    [[gnu::always_inline]] void lock() { m_lock.lock(); }
 
 private:
     Lock& m_lock;
diff --git a/AK/RetainPtr.h b/AK/RetainPtr.h
index b98278ccee..4a831276e3 100644
--- a/AK/RetainPtr.h
+++ b/AK/RetainPtr.h
@@ -1,6 +1,5 @@
 #pragma once
 
-#include "Compiler.h"
 #include "Types.h"
 
 namespace AK {
diff --git a/AK/StdLibExtras.h b/AK/StdLibExtras.h
index b5e7515d29..d4a03a95d5 100644
--- a/AK/StdLibExtras.h
+++ b/AK/StdLibExtras.h
@@ -11,7 +11,7 @@
 
 void* mmx_memcpy(void* to, const void* from, size_t);
 
-ALWAYS_INLINE void fast_dword_copy(dword* dest, const dword* src, size_t count)
+[[gnu::always_inline]] inline void fast_dword_copy(dword* dest, const dword* src, size_t count)
 {
     if (count >= 256) {
         mmx_memcpy(dest, src, count * sizeof(count));
@@ -25,7 +25,7 @@ ALWAYS_INLINE void fast_dword_copy(dword* dest, const dword* src, size_t count)
     );
 }
 
-ALWAYS_INLINE void fast_dword_fill(dword* dest, dword value, size_t count)
+[[gnu::always_inline]] inline void fast_dword_fill(dword* dest, dword value, size_t count)
 {
     asm volatile(
         "rep stosl\n"
diff --git a/AK/kmalloc.h b/AK/kmalloc.h
index 3c8102c0fd..f02e591dfd 100644
--- a/AK/kmalloc.h
+++ b/AK/kmalloc.h
@@ -1,7 +1,5 @@
 #pragma once
 
-#include "Compiler.h"
-
 #if defined(SERENITY) && defined(KERNEL)
 #define AK_MAKE_ETERNAL \
 public: \
@@ -18,11 +16,10 @@ private:
 
 extern "C" {
 
-void* kcalloc(size_t nmemb, size_t size);
-void* kmalloc(size_t size) MALLOC_ATTR;
+[[gnu::malloc, gnu::returns_nonnull]] void* kmalloc(size_t size);
+[[gnu::malloc, gnu::returns_nonnull]] void* kmalloc_eternal(size_t);
+[[gnu::returns_nonnull]] void* krealloc(void* ptr, size_t size);
 void kfree(void* ptr);
-void* krealloc(void* ptr, size_t size);
-void* kmalloc_eternal(size_t) MALLOC_ATTR;
 
 }
 
diff --git a/AK/printf.cpp b/AK/printf.cpp
index b40ee07ca7..831ab41169 100644
--- a/AK/printf.cpp
+++ b/AK/printf.cpp
@@ -2,7 +2,7 @@ typedef unsigned char byte;
 typedef unsigned short word;
 typedef unsigned int dword;
 
-ALWAYS_INLINE size_t strlen(const char* str)
+[[gnu::always_inline]] inline size_t strlen(const char* str)
 {
     size_t len = 0;
     while (*(str++))
@@ -13,7 +13,7 @@ ALWAYS_INLINE size_t strlen(const char* str)
 static constexpr const char* h = "0123456789abcdef";
 
 template<typename PutChFunc>
-ALWAYS_INLINE int print_hex(PutChFunc putch, char*& bufptr, dword number, byte fields)
+[[gnu::always_inline]] int print_hex(PutChFunc putch, char*& bufptr, dword number, byte fields)
 {
     int ret = 0;
     byte shr_count = fields * 4;
@@ -26,7 +26,7 @@ ALWAYS_INLINE int print_hex(PutChFunc putch, char*& bufptr, dword number, byte f
 }
 
 template<typename PutChFunc>
-ALWAYS_INLINE int print_number(PutChFunc putch, char*& bufptr, dword number, bool leftPad, bool zeroPad, dword fieldWidth)
+[[gnu::always_inline]] int print_number(PutChFunc putch, char*& bufptr, dword number, bool leftPad, bool zeroPad, dword fieldWidth)
 {
     dword divisor = 1000000000;
     char ch;
@@ -67,7 +67,7 @@ ALWAYS_INLINE int print_number(PutChFunc putch, char*& bufptr, dword number, boo
 }
 
 template<typename PutChFunc>
-ALWAYS_INLINE int print_octal_number(PutChFunc putch, char*& bufptr, dword number, bool leftPad, bool zeroPad, dword fieldWidth)
+[[gnu::always_inline]] int print_octal_number(PutChFunc putch, char*& bufptr, dword number, bool leftPad, bool zeroPad, dword fieldWidth)
 {
     dword divisor = 134217728;
     char ch;
@@ -108,7 +108,7 @@ ALWAYS_INLINE int print_octal_number(PutChFunc putch, char*& bufptr, dword numbe
 }
 
 template<typename PutChFunc>
-ALWAYS_INLINE int print_string(PutChFunc putch, char*& bufptr, const char* str, bool leftPad, dword fieldWidth)
+[[gnu::always_inline]] int print_string(PutChFunc putch, char*& bufptr, const char* str, bool leftPad, dword fieldWidth)
 {
     size_t len = strlen(str);
     if (!fieldWidth || fieldWidth < len)
@@ -129,7 +129,7 @@ ALWAYS_INLINE int print_string(PutChFunc putch, char*& bufptr, const char* str,
 
 
 template<typename PutChFunc>
-ALWAYS_INLINE int print_signed_number(PutChFunc putch, char*& bufptr, int number, bool leftPad, bool zeroPad, dword fieldWidth)
+[[gnu::always_inline]] int print_signed_number(PutChFunc putch, char*& bufptr, int number, bool leftPad, bool zeroPad, dword fieldWidth)
 {
     if (number < 0) {
         putch(bufptr, '-');
@@ -139,7 +139,7 @@ ALWAYS_INLINE int print_signed_number(PutChFunc putch, char*& bufptr, int number
 }
 
 template<typename PutChFunc>
-ALWAYS_INLINE int printf_internal(PutChFunc putch, char* buffer, const char*& fmt, char*& ap)
+[[gnu::always_inline]] int printf_internal(PutChFunc putch, char* buffer, const char*& fmt, char*& ap)
 {
     const char *p;
 
diff --git a/Applications/Terminal/Terminal.cpp b/Applications/Terminal/Terminal.cpp
index 3e169505f4..97b6ea5e6f 100644
--- a/Applications/Terminal/Terminal.cpp
+++ b/Applications/Terminal/Terminal.cpp
@@ -481,27 +481,26 @@ void Terminal::on_char(byte ch)
             return;
         }
         m_escape_state = ExpectXtermFinal;
-        // fall through
+        [[fallthrough]];
     case ExpectXtermFinal:
         m_escape_state = Normal;
         if (ch == '\007')
             execute_xterm_command();
         return;
-
     case ExpectParameter:
         if (is_valid_parameter_character(ch)) {
             m_parameters.append(ch);
             return;
         }
         m_escape_state = ExpectIntermediate;
-        // fall through
+        [[fallthrough]];
     case ExpectIntermediate:
         if (is_valid_intermediate_character(ch)) {
             m_intermediates.append(ch);
             return;
         }
         m_escape_state = ExpectFinal;
-        // fall through
+        [[fallthrough]];
     case ExpectFinal:
         if (is_valid_final_character(ch)) {
             m_escape_state = Normal;
diff --git a/Kernel/Console.h b/Kernel/Console.h
index 4ef6a4684e..2d3cc77009 100644
--- a/Kernel/Console.h
+++ b/Kernel/Console.h
@@ -1,7 +1,6 @@
 #pragma once
 
 #include <AK/CircularQueue.h>
-#include <AK/Compiler.h>
 #include <AK/Vector.h>
 #include <Kernel/CharacterDevice.h>
 
@@ -14,7 +13,7 @@ public:
 class Console final : public CharacterDevice {
     AK_MAKE_ETERNAL
 public:
-    static Console& the() PURE;
+    static Console& the();
 
     Console();
     virtual ~Console() override;
diff --git a/Kernel/DevPtsFS.h b/Kernel/DevPtsFS.h
index 94587e0031..33a08f0c70 100644
--- a/Kernel/DevPtsFS.h
+++ b/Kernel/DevPtsFS.h
@@ -8,7 +8,7 @@ class SlavePTY;
 
 class DevPtsFS final : public SynthFS {
 public:
-    static DevPtsFS& the() PURE;
+    [[gnu::pure]] static DevPtsFS& the();
 
     virtual ~DevPtsFS() override;
     static RetainPtr<DevPtsFS> create();
diff --git a/Kernel/KSyms.cpp b/Kernel/KSyms.cpp
index 9bc26ddb8b..b5913b582c 100644
--- a/Kernel/KSyms.cpp
+++ b/Kernel/KSyms.cpp
@@ -74,11 +74,11 @@ static void load_ksyms_from_data(const ByteBuffer& buffer)
 void dump_backtrace(bool use_ksyms)
 {
     if (!current) {
-        HANG;
+        hang();
         return;
     }
     if (use_ksyms && !ksyms_ready) {
-        HANG;
+        hang();
         return;
     }
     struct RecognizedSymbol {
diff --git a/Kernel/KSyms.h b/Kernel/KSyms.h
index d0551c5307..a7f8c33fa3 100644
--- a/Kernel/KSyms.h
+++ b/Kernel/KSyms.h
@@ -8,7 +8,7 @@ struct KSym {
     const char* name;
 };
 
-const KSym* ksymbolicate(dword address) PURE;
+const KSym* ksymbolicate(dword address);
 void load_ksyms();
 void init_ksyms();
 
diff --git a/Kernel/Keyboard.h b/Kernel/Keyboard.h
index 6cf580b801..35bda98164 100644
--- a/Kernel/Keyboard.h
+++ b/Kernel/Keyboard.h
@@ -29,7 +29,7 @@ public:
         bool is_press() const { return flags & Is_Press; }
     };
 
-    static Keyboard& the() PURE;
+    [[gnu::pure]] static Keyboard& the();
 
     virtual ~Keyboard() override;
     Keyboard();
diff --git a/Kernel/MemoryManager.h b/Kernel/MemoryManager.h
index a7243d5b97..4cf90b3df8 100644
--- a/Kernel/MemoryManager.h
+++ b/Kernel/MemoryManager.h
@@ -217,7 +217,7 @@ class MemoryManager {
     friend class VMObject;
     friend ByteBuffer procfs$mm(InodeIdentifier);
 public:
-    static MemoryManager& the() PURE;
+    [[gnu::pure]] static MemoryManager& the();
 
     static void initialize();
 
diff --git a/Kernel/ProcFS.h b/Kernel/ProcFS.h
index 9c5591bff0..c57e08fdd1 100644
--- a/Kernel/ProcFS.h
+++ b/Kernel/ProcFS.h
@@ -11,7 +11,7 @@ class ProcFSInode;
 class ProcFS final : public FS {
     friend class ProcFSInode;
 public:
-    static ProcFS& the() PURE;
+    [[gnu::pure]] static ProcFS& the();
 
     virtual ~ProcFS() override;
     static RetainPtr<ProcFS> create();
diff --git a/Kernel/Process.h b/Kernel/Process.h
index f030acdf24..66c7528966 100644
--- a/Kernel/Process.h
+++ b/Kernel/Process.h
@@ -171,8 +171,8 @@ public:
     int sys$lseek(int fd, off_t, int whence);
     int sys$kill(pid_t pid, int sig);
     int sys$geterror() { return m_error; }
-    void sys$exit(int status) NORETURN;
-    void sys$sigreturn() NORETURN;
+    [[noreturn]] void sys$exit(int status);
+    [[noreturn]] void sys$sigreturn();
     pid_t sys$waitpid(pid_t, int* wstatus, int options);
     void* sys$mmap(const Syscall::SC_mmap_params*);
     int sys$munmap(void*, size_t size);
@@ -230,8 +230,8 @@ public:
 
     static void initialize();
 
-    void crash() NORETURN;
-    static int reap(Process&) WARN_UNUSED_RESULT;
+    [[noreturn]] void crash();
+    [[nodiscard]] static int reap(Process&);
 
     const TTY* tty() const { return m_tty; }
     void set_tty(TTY* tty) { m_tty = tty; }
diff --git a/Kernel/StdLib.cpp b/Kernel/StdLib.cpp
index 87e1df0506..03c02e0ae9 100644
--- a/Kernel/StdLib.cpp
+++ b/Kernel/StdLib.cpp
@@ -125,8 +125,7 @@ int memcmp(const void* v1, const void* v2, size_t n)
     return 0;
 }
 
-void __cxa_pure_virtual() NORETURN;
-void __cxa_pure_virtual()
+[[noreturn]] void __cxa_pure_virtual()
 {
     ASSERT_NOT_REACHED();
 }
diff --git a/Kernel/TSS.h b/Kernel/TSS.h
index 676750e454..f3e370439e 100644
--- a/Kernel/TSS.h
+++ b/Kernel/TSS.h
@@ -2,7 +2,7 @@
 
 #include <AK/Types.h>
 
-struct TSS32 {
+struct [[gnu::packed]] TSS32 {
     word backlink, __blh;
     dword esp0;
     word ss0, __ss0h;
@@ -20,4 +20,4 @@ struct TSS32 {
     word gs, __gsh;
     word ldt, __ldth;
     word trace, iomapbase;
-} PACKED;
+};
diff --git a/Kernel/VirtualFileSystem.h b/Kernel/VirtualFileSystem.h
index 6c3fe71c40..7887005c73 100644
--- a/Kernel/VirtualFileSystem.h
+++ b/Kernel/VirtualFileSystem.h
@@ -54,7 +54,7 @@ public:
         RetainPtr<FS> m_guest_fs;
     };
 
-    static VFS& the() PURE;
+    [[gnu::pure]] static VFS& the();
 
     VFS();
     ~VFS();
diff --git a/Kernel/i386.cpp b/Kernel/i386.cpp
index 1336b8aa11..ccf27c9f33 100644
--- a/Kernel/i386.cpp
+++ b/Kernel/i386.cpp
@@ -10,10 +10,10 @@
 
 //#define PAGE_FAULT_DEBUG
 
-struct DescriptorTablePointer {
+struct [[gnu::packed]] DescriptorTablePointer {
     word size;
     void* address;
-} PACKED;
+};
 
 static DescriptorTablePointer s_idtr;
 static DescriptorTablePointer s_gdtr;
@@ -144,9 +144,9 @@ void exception_6_handler(RegisterDump& regs)
 
     if (current->is_ring0()) {
         kprintf("Oh shit, we've crashed in ring 0 :(\n");
-        HANG;
+        hang();
     }
-    HANG;
+    hang();
 
     current->crash();
 }
@@ -219,7 +219,7 @@ void exception_13_handler(RegisterDumpWithExceptionCode& regs)
 
     if (current->is_ring0()) {
         kprintf("Oh shit, we've crashed in ring 0 :(\n");
-        HANG;
+        hang();
     }
 
     current->crash();
@@ -313,7 +313,7 @@ void exception_14_handler(RegisterDumpWithExceptionCode& regs)
         asm ("movl %%cr3, %%eax":"=a"(cr3)); \
         asm ("movl %%cr4, %%eax":"=a"(cr4)); \
         kprintf("CR0=%x CR2=%x CR3=%x CR4=%x\n", cr0, cr2, cr3, cr4); \
-        HANG; \
+        hang(); \
     }
 
 EH(0, "Divide error")
@@ -385,7 +385,7 @@ void gdt_init()
 static void unimp_trap()
 {
     kprintf("Unhandled IRQ.");
-    HANG;
+    hang();
 }
 
 void register_irq_handler(byte irq, IRQHandler& handler)
diff --git a/Kernel/i386.h b/Kernel/i386.h
index bede94a97c..4dc56620d4 100644
--- a/Kernel/i386.h
+++ b/Kernel/i386.h
@@ -6,7 +6,7 @@
 #define PAGE_SIZE 4096
 #define PAGE_MASK 0xfffff000
 
-union Descriptor {
+union [[gnu::packed]] Descriptor {
     struct {
         word limit_lo;
         word base_lo;
@@ -55,7 +55,7 @@ union Descriptor {
         limit_lo = (dword)l & 0xffff;
         limit_hi = ((dword)l >> 16) & 0xff;
     }
-} PACKED;
+};
 
 class IRQHandler;
 
@@ -73,7 +73,12 @@ void gdt_free_entry(word);
 Descriptor& get_gdt_entry(word selector);
 void write_gdt_entry(word selector, Descriptor&);
 
-#define HANG asm volatile( "cli; hlt" );
+[[noreturn]] static inline void hang()
+{
+    asm volatile("cli; hlt");
+    for (;;) { }
+}
+
 #define LSW(x) ((dword)(x) & 0xFFFF)
 #define MSW(x) (((dword)(x) >> 16) & 0xFFFF)
 #define LSB(x) ((x) & 0xFF)
@@ -182,7 +187,7 @@ private:
     LinearAddress m_laddr;
 };
 
-struct RegisterDump {
+struct [[gnu::packed]] RegisterDump {
     word ss;
     word gs;
     word fs;
@@ -202,9 +207,9 @@ struct RegisterDump {
     dword eflags;
     dword esp_if_crossRing;
     word ss_if_crossRing;
-} PACKED;
+};
 
-struct RegisterDumpWithExceptionCode {
+struct [[gnu::packed]] RegisterDumpWithExceptionCode {
     word ss;
     word gs;
     word fs;
@@ -226,7 +231,7 @@ struct RegisterDumpWithExceptionCode {
     dword eflags;
     dword esp_if_crossRing;
     word ss_if_crossRing;
-} PACKED;
+};
 
 struct FPUState {
     dword cwd;
diff --git a/Kernel/init.cpp b/Kernel/init.cpp
index 632c00b2f4..2c68fc80bd 100644
--- a/Kernel/init.cpp
+++ b/Kernel/init.cpp
@@ -44,8 +44,7 @@ NullDevice* dev_null;
 VFS* vfs;
 
 #ifdef STRESS_TEST_SPAWNING
-static void spawn_stress() NORETURN;
-static void spawn_stress()
+[[noreturn]] static void spawn_stress()
 {
     dword last_sum_alloc = sum_alloc;
 
@@ -62,8 +61,7 @@ static void spawn_stress()
 }
 #endif
 
-static void init_stage2() NORETURN;
-static void init_stage2()
+[[noreturn]] static void init_stage2()
 {
     Syscall::initialize();
 
@@ -135,8 +133,7 @@ static void init_stage2()
     ASSERT_NOT_REACHED();
 }
 
-void init() NORETURN;
-void init()
+[[noreturn]] void init()
 {
     cli();
 
diff --git a/Kernel/kassert.h b/Kernel/kassert.h
index f799f90c72..774afe2a62 100644
--- a/Kernel/kassert.h
+++ b/Kernel/kassert.h
@@ -3,7 +3,7 @@
 #include "kprintf.h"
 #include "i386.h"
 
-void __assertion_failed(const char* msg, const char* file, unsigned line, const char* func) NORETURN;
+[[noreturn]] void __assertion_failed(const char* msg, const char* file, unsigned line, const char* func);
 
 #define ASSERT(expr) (static_cast<bool>(expr) ? (void)0 : __assertion_failed(#expr, __FILE__, __LINE__, __PRETTY_FUNCTION__))
 #define CRASH() do { asm volatile("ud2"); } while(0)
diff --git a/Kernel/kmalloc.cpp b/Kernel/kmalloc.cpp
index a61a1b48a0..2447914459 100644
--- a/Kernel/kmalloc.cpp
+++ b/Kernel/kmalloc.cpp
@@ -14,11 +14,10 @@
 
 #define SANITIZE_KMALLOC
 
-typedef struct
-{
+struct [[gnu::packed]] allocation_t {
     dword start;
     dword nchunk;
-} PACKED allocation_t;
+};
 
 #define CHUNK_SIZE  128
 #define POOL_SIZE   (1024 * 1024)
@@ -103,8 +102,7 @@ void* kmalloc_impl(dword size)
 
     if (sum_free < real_size) {
         kprintf("%s<%u> kmalloc(): PANIC! Out of memory (sucks, dude)\nsum_free=%u, real_size=%x\n", current->name().characters(), current->pid(), sum_free, real_size);
-        HANG;
-        return 0L;
+        hang();
     }
 
     chunks_needed = real_size / CHUNK_SIZE;
@@ -164,9 +162,7 @@ void* kmalloc_impl(dword size)
     }
 
     kprintf("%s<%u> kmalloc(): PANIC! Out of memory (no suitable block for size %u)\n", current->name().characters(), current->pid(), size);
-    HANG;
-
-    return nullptr;
+    hang();
 }
 
 void kfree(void *ptr)
diff --git a/Kernel/kmalloc.h b/Kernel/kmalloc.h
index 82c47e3354..19e9fb9644 100644
--- a/Kernel/kmalloc.h
+++ b/Kernel/kmalloc.h
@@ -1,12 +1,14 @@
 #pragma once
 
+#include <AK/Types.h>
+
 //#define KMALLOC_DEBUG_LARGE_ALLOCATIONS
 
 void kmalloc_init();
-void* kmalloc_impl(dword size) __attribute__ ((malloc));
-void* kmalloc_eternal(size_t) __attribute__ ((malloc));
-void* kmalloc_page_aligned(size_t) __attribute__ ((malloc));
-void* kmalloc_aligned(size_t, size_t alignment) __attribute__ ((malloc));
+[[gnu::malloc, gnu::returns_nonnull, gnu::alloc_size(1)]] void* kmalloc_impl(size_t);
+[[gnu::malloc, gnu::returns_nonnull, gnu::alloc_size(1)]] void* kmalloc_eternal(size_t);
+[[gnu::malloc, gnu::returns_nonnull, gnu::alloc_size(1)]] void* kmalloc_page_aligned(size_t);
+[[gnu::malloc, gnu::returns_nonnull, gnu::alloc_size(1)]] void* kmalloc_aligned(size_t, size_t alignment);
 void kfree(void*);
 void kfree_aligned(void*);
 
@@ -20,7 +22,7 @@ extern volatile size_t kmalloc_sum_page_aligned;
 inline void* operator new(size_t, void* p) { return p; }
 inline void* operator new[](size_t, void* p) { return p; }
 
-ALWAYS_INLINE void* kmalloc(size_t size)
+[[gnu::always_inline]] inline void* kmalloc(size_t size)
 {
 #ifdef KMALLOC_DEBUG_LARGE_ALLOCATIONS
     // Any kernel allocation >= 1M is 99.9% a bug.
diff --git a/Kernel/kprintf.h b/Kernel/kprintf.h
index 2406b9c07d..29c2d15bd4 100644
--- a/Kernel/kprintf.h
+++ b/Kernel/kprintf.h
@@ -1,7 +1,5 @@
 #pragma once
 
-#include <AK/Compiler.h>
-
 extern "C" {
 int dbgprintf(const char *fmt, ...);
 int kprintf(const char *fmt, ...);
diff --git a/Kernel/types.h b/Kernel/types.h
index 45cd0bb45d..efa5a31977 100644
--- a/Kernel/types.h
+++ b/Kernel/types.h
@@ -1,11 +1,7 @@
 #pragma once
 
-#include <AK/Compiler.h>
 #include <AK/Types.h>
 
-#define PACKED __attribute__ ((packed))
-#define PURE __attribute__ ((pure))
-
 typedef dword __u32;
 typedef word __u16;
 typedef byte __u8;
@@ -43,10 +39,10 @@ typedef dword nlink_t;
 typedef dword blksize_t;
 typedef dword blkcnt_t;
 
-struct FarPtr {
+struct [[gnu::packed]] FarPtr {
     dword offset { 0 };
     word selector { 0 };
-} PACKED;
+};
 
 class PhysicalAddress {
 public:
diff --git a/LibC/assert.h b/LibC/assert.h
index 25ea654db6..36be4b57f0 100644
--- a/LibC/assert.h
+++ b/LibC/assert.h
@@ -4,7 +4,7 @@
 
 __BEGIN_DECLS
 
-void __assertion_failed(const char* msg, const char* file, unsigned line, const char* func) __attribute__ ((noreturn));
+[[noreturn]] void __assertion_failed(const char* msg, const char* file, unsigned line, const char* func);
 
 #define assert(expr) ((expr) ? (void)0 : __assertion_failed(#expr, __FILE__, __LINE__, __PRETTY_FUNCTION__))
 #define CRASH() do { asm volatile("ud2"); } while(0)
diff --git a/LibC/ctype.h b/LibC/ctype.h
index 41178f5cb4..f3ac9d2218 100644
--- a/LibC/ctype.h
+++ b/LibC/ctype.h
@@ -4,41 +4,41 @@
 
 __BEGIN_DECLS
 
-ALWAYS_INLINE int isascii(int ch)
+[[gnu::always_inline]] inline int isascii(int ch)
 {
     return (ch & ~0x7f) == 0;
 }
 
-ALWAYS_INLINE int isspace(int ch)
+[[gnu::always_inline]] inline int isspace(int ch)
 {
     return ch == ' ' || ch == '\f' || ch == '\n' || ch == '\r' || ch == '\t' || ch == '\v';
 }
 
-ALWAYS_INLINE int islower(int c)
+[[gnu::always_inline]] inline int islower(int c)
 {
     return c >= 'a' && c <= 'z';
 }
 
-ALWAYS_INLINE int isupper(int c)
+[[gnu::always_inline]] inline int isupper(int c)
 {
     return c >= 'A' && c <= 'Z';
 }
 
-ALWAYS_INLINE int tolower(int c)
+[[gnu::always_inline]] inline int tolower(int c)
 {
     if (isupper(c))
         return c | 0x20;
     return c;
 }
 
-ALWAYS_INLINE int toupper(int c)
+[[gnu::always_inline]] inline int toupper(int c)
 {
     if (islower(c))
         return c & ~0x20;
     return c;
 }
 
-ALWAYS_INLINE int isdigit(int c)
+[[gnu::always_inline]] inline int isdigit(int c)
 {
     return c >= '0' && c <= '9';
 }
diff --git a/LibC/dirent.cpp b/LibC/dirent.cpp
index c511b9dad6..ef1ec33bc2 100644
--- a/LibC/dirent.cpp
+++ b/LibC/dirent.cpp
@@ -35,7 +35,7 @@ int closedir(DIR* dirp)
     return rc;
 }
 
-struct sys_dirent {
+struct [[gnu::packed]] sys_dirent {
     ino_t ino;
     byte file_type;
     size_t namelen;
@@ -44,7 +44,7 @@ struct sys_dirent {
     {
         return sizeof(ino_t) + sizeof(byte) + sizeof(size_t) + sizeof(char) * namelen;
     }
-} __attribute__ ((packed));
+};
 
 dirent* readdir(DIR* dirp)
 {
diff --git a/LibC/entry.cpp b/LibC/entry.cpp
index ec610296f9..591c85a969 100644
--- a/LibC/entry.cpp
+++ b/LibC/entry.cpp
@@ -3,15 +3,17 @@
 #include <Kernel/Syscall.h>
 #include <AK/StringImpl.h>
 
-extern "C" int main(int, char**);
+extern "C" {
+
+int main(int, char**);
 
 int errno;
 char** environ;
 
-extern "C" void __malloc_init();
-extern "C" void __stdio_init();
+void __malloc_init();
+void __stdio_init();
 
-extern "C" int _start()
+int _start()
 {
     errno = 0;
 
@@ -39,8 +41,9 @@ epilogue:
     return 20150614;
 }
 
-extern "C" void __cxa_pure_virtual() NORETURN;
-extern "C" void __cxa_pure_virtual()
+[[noreturn]] void __cxa_pure_virtual()
 {
     ASSERT_NOT_REACHED();
 }
+
+}
diff --git a/LibC/stdlib.h b/LibC/stdlib.h
index bc673b0a02..a07477008f 100644
--- a/LibC/stdlib.h
+++ b/LibC/stdlib.h
@@ -9,16 +9,16 @@ __BEGIN_DECLS
 #define EXIT_FAILURE 1
 #define MB_CUR_MAX 1
 
-void* malloc(size_t) __MALLOC;
+[[gnu::malloc, gnu::returns_nonnull, gnu::alloc_size(1)]] void* malloc(size_t);
+[[gnu::malloc, gnu::returns_nonnull, gnu::alloc_size(1, 2)]] void* calloc(size_t nmemb, size_t);
 void free(void*);
-void* calloc(size_t nmemb, size_t);
-void* realloc(void *ptr, size_t);
+[[gnu::returns_nonnull]] void* realloc(void *ptr, size_t);
 char* getenv(const char* name);
 int atoi(const char*);
 long atol(const char*);
 void qsort(void* base, size_t nmemb, size_t size, int (*compar)(const void *, const void *));
-void exit(int status) __NORETURN;
-void abort() __NORETURN;
+[[noreturn]] void exit(int status);
+[[noreturn]] void abort();
 char* ptsname(int fd);
 int ptsname_r(int fd, char* buffer, size_t);
 int abs(int);
diff --git a/LibC/sys/cdefs.h b/LibC/sys/cdefs.h
index e26352ee82..9fcd9b1682 100644
--- a/LibC/sys/cdefs.h
+++ b/LibC/sys/cdefs.h
@@ -2,10 +2,6 @@
 
 #define _POSIX_VERSION 200809L
 
-#define ALWAYS_INLINE inline __attribute__ ((always_inline))
-#define __NORETURN __attribute__ ((noreturn))
-#define __MALLOC __attribute__ ((malloc))
-
 #ifdef __cplusplus
 #define __BEGIN_DECLS extern "C" {
 #define __END_DECLS }
diff --git a/SharedGraphics/Font.cpp b/SharedGraphics/Font.cpp
index f5b29d5d04..7191ae0d30 100644
--- a/SharedGraphics/Font.cpp
+++ b/SharedGraphics/Font.cpp
@@ -36,14 +36,14 @@ static constexpr const char* error_glyph {
 static Font* s_default_font;
 static Font* s_default_bold_font;
 
-struct FontFileHeader {
+struct [[gnu::packed]] FontFileHeader {
     char magic[4];
     byte glyph_width;
     byte glyph_height;
     byte type;
     byte unused[7];
     char name[64];
-} PACKED;
+};
 
 static inline constexpr size_t font_file_size(unsigned glyph_height)
 {
diff --git a/SharedGraphics/Painter.cpp b/SharedGraphics/Painter.cpp
index e65ecbcbad..1150fb50c3 100644
--- a/SharedGraphics/Painter.cpp
+++ b/SharedGraphics/Painter.cpp
@@ -291,7 +291,7 @@ void Painter::blit(const Point& position, const GraphicsBitmap& source, const Re
     }
 }
 
-FLATTEN void Painter::draw_glyph(const Point& point, char ch, Color color)
+[[gnu::flatten]] void Painter::draw_glyph(const Point& point, char ch, Color color)
 {
     draw_bitmap(point, font().glyph_bitmap(ch), color);
 }
@@ -332,7 +332,7 @@ void Painter::set_pixel(const Point& p, Color color)
     m_target->scanline(point.y())[point.x()] = color.value();
 }
 
-ALWAYS_INLINE void Painter::set_pixel_with_draw_op(dword& pixel, const Color& color)
+[[gnu::always_inline]] void Painter::set_pixel_with_draw_op(dword& pixel, const Color& color)
 {
     if (m_draw_op == DrawOp::Copy)
         pixel = color.value();