Kernel/riscv64: Make the kernel compile

This commits inserts TODOs into all necessary places to make the kernel
compile on riscv64!

Kernel/Arch/riscv64/SafeMem.cpp

@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2022, Timon Kruiper <timonkruiper@gmail.com>
+ * Copyright (c) 2023, Daniel Bertalan <dani@danielbertalan.dev>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Arch/RegisterState.h>
+#include <Kernel/Arch/SafeMem.h>
+#include <Kernel/Library/StdLib.h>
+
+#define CODE_SECTION(section_name) __attribute__((section(section_name)))
+
+extern "C" u8 start_of_safemem_text[];
+extern "C" u8 end_of_safemem_text[];
+
+extern "C" u8 start_of_safemem_atomic_text[];
+extern "C" u8 end_of_safemem_atomic_text[];
+
+namespace Kernel {
+
+CODE_SECTION(".text.safemem")
+NEVER_INLINE FLATTEN bool safe_memset(void* dest_ptr, int c, size_t n, void*& fault_at)
+{
+    // FIXME: Actually implement a safe memset.
+    auto* dest = static_cast<u8*>(dest_ptr);
+    for (; n--;)
+        *dest++ = c;
+    fault_at = nullptr;
+    return true;
+}
+
+CODE_SECTION(".text.safemem")
+NEVER_INLINE FLATTEN ssize_t safe_strnlen(char const* str, unsigned long max_n, void*& fault_at)
+{
+    // FIXME: Actually implement a safe strnlen.
+    size_t len = 0;
+    for (; len < max_n && *str; str++)
+        len++;
+    fault_at = nullptr;
+    return len;
+}
+
+CODE_SECTION(".text.safemem")
+NEVER_INLINE FLATTEN bool safe_memcpy(void* dest_ptr, void const* src_ptr, unsigned long n, void*& fault_at)
+{
+    // FIXME: Actually implement a safe memcpy.
+    auto* pd = static_cast<u8*>(dest_ptr);
+    auto const* ps = static_cast<u8 const*>(src_ptr);
+    for (; n--;)
+        *pd++ = *ps++;
+    fault_at = nullptr;
+    return true;
+}
+
+CODE_SECTION(".text.safemem.atomic")
+NEVER_INLINE FLATTEN Optional<bool> safe_atomic_compare_exchange_relaxed(u32 volatile* var, u32& expected, u32 val)
+{
+    // FIXME: Handle access faults.
+    return AK::atomic_compare_exchange_strong(var, expected, val, AK::memory_order_relaxed);
+}
+
+CODE_SECTION(".text.safemem.atomic")
+NEVER_INLINE FLATTEN Optional<u32> safe_atomic_load_relaxed(u32 volatile* var)
+{
+    // FIXME: Handle access faults.
+    return AK::atomic_load(var, AK::memory_order_relaxed);
+}
+
+CODE_SECTION(".text.safemem.atomic")
+NEVER_INLINE FLATTEN Optional<u32> safe_atomic_fetch_add_relaxed(u32 volatile* var, u32 val)
+{
+    // FIXME: Handle access faults.
+    return AK::atomic_fetch_add(var, val, AK::memory_order_relaxed);
+}
+
+CODE_SECTION(".text.safemem.atomic")
+NEVER_INLINE FLATTEN Optional<u32> safe_atomic_exchange_relaxed(u32 volatile* var, u32 val)
+{
+    // FIXME: Handle access faults.
+    return AK::atomic_exchange(var, val, AK::memory_order_relaxed);
+}
+
+CODE_SECTION(".text.safemem.atomic")
+NEVER_INLINE FLATTEN bool safe_atomic_store_relaxed(u32 volatile* var, u32 val)
+{
+    // FIXME: Handle access faults.
+    AK::atomic_store(var, val);
+    return true;
+}
+
+bool handle_safe_access_fault(RegisterState& regs, FlatPtr fault_address)
+{
+    FlatPtr ip = regs.ip();
+
+    if (ip >= (FlatPtr)&start_of_safemem_text && ip < (FlatPtr)&end_of_safemem_text) {
+        dbgln("FIXME: Faulted while accessing userspace address {:p}.", fault_address);
+        dbgln("       We need to jump back into the appropriate SafeMem function, set fault_at and return failure.");
+        TODO_RISCV64();
+    } else if (ip >= (FlatPtr)&start_of_safemem_atomic_text && ip < (FlatPtr)&end_of_safemem_atomic_text) {
+        dbgln("FIXME: Faulted while accessing userspace address {:p}.", fault_address);
+        dbgln("       We need to jump back into the appropriate atomic SafeMem function and return failure.");
+        TODO_RISCV64();
+    }
+
+    return false;
+}
+
+}