Prekernel: Add support for assertion printing

This is done by using a FixedStringBuffer as the foundation to perform
string formatting, which ensures that we avoid memory allocations in
the prekernel stage.

AK/FixedStringBuffer.h

@@ -12,7 +12,7 @@
 #include <AK/TypedTransfer.h>
 #include <AK/Userspace.h>
 
-#ifdef KERNEL
+#if defined(KERNEL) && !defined(PREKERNEL)
 #    include <Kernel/Arch/SafeMem.h>
 #    include <Kernel/Arch/SmapDisabler.h>
 #    include <Kernel/Memory/MemorySections.h>
@@ -64,7 +64,7 @@ public:
             m_storage[index] = '\0';
     }
 
-#ifdef KERNEL
+#if defined(KERNEL) && !defined(PREKERNEL)
     ErrorOr<void> copy_characters_from_user(Userspace<char const*> user_str, size_t user_str_size)
     {
         if (user_str_size > Size)

AK/Format.cpp

@@ -16,7 +16,8 @@
 #    include <serenity.h>
 #endif
 
-#ifdef KERNEL
+#if defined(PREKERNEL)
+#elif defined(KERNEL)
 #    include <Kernel/Tasks/Process.h>
 #    include <Kernel/Tasks/Thread.h>
 #    include <Kernel/Time/TimeManagement.h>
@@ -1152,7 +1153,9 @@ void vdbg(StringView fmtstr, TypeErasedFormatParams& params, bool newline)
     StringBuilder builder;
 
     if (is_rich_debug_enabled) {
-#ifdef KERNEL
+#if defined(PREKERNEL)
+        ;
+#elif defined(KERNEL)
         if (Kernel::Processor::is_initialized() && TimeManagement::is_initialized()) {
             auto time = TimeManagement::the().monotonic_time(TimePrecision::Coarse);
             if (Kernel::Thread::current()) {
@@ -1195,7 +1198,7 @@ void vdbg(StringView fmtstr, TypeErasedFormatParams& params, bool newline)
     auto const string = builder.string_view();
 
 #ifdef AK_OS_SERENITY
-#    ifdef KERNEL
+#    if defined(KERNEL) && !defined(PREKERNEL)
     if (!Kernel::Processor::is_initialized()) {
         kernelearlyputstr(string.characters_without_null_termination(), string.length());
         return;
@@ -1205,7 +1208,7 @@ void vdbg(StringView fmtstr, TypeErasedFormatParams& params, bool newline)
     dbgputstr(string.characters_without_null_termination(), string.length());
 }
 
-#ifdef KERNEL
+#if defined(KERNEL) && !defined(PREKERNEL)
 void vdmesgln(StringView fmtstr, TypeErasedFormatParams& params)
 {
     StringBuilder builder;

AK/StringUtils.cpp

@@ -14,7 +14,9 @@
 #include <AK/StringView.h>
 #include <AK/Vector.h>
 
-#ifdef KERNEL
+#if defined(PREKERNEL)
+#    include <Kernel/Library/MiniStdLib.h>
+#elif defined(KERNEL)
 #    include <Kernel/Library/StdLib.h>
 #else
 #    include <AK/ByteString.h>

Kernel/Arch/x86_64/DebugOutput.cpp

@@ -5,10 +5,13 @@
  */
 
 #include <Kernel/Arch/DebugOutput.h>
-#include <Kernel/Arch/Processor.h>
 #include <Kernel/Arch/x86_64/BochsDebugOutput.h>
 #include <Kernel/Arch/x86_64/IO.h>
 
+#if !defined(PREKERNEL)
+#    include <Kernel/Arch/Processor.h>
+#endif
+
 namespace Kernel {
 
 static constexpr u16 serial_com1_io_port = 0x3F8;
@@ -35,8 +38,13 @@ void debug_output(char ch)
         serial_ready = true;
     }
 
-    while ((IO::in8(serial_com1_io_port + 5) & 0x20) == 0)
+    while ((IO::in8(serial_com1_io_port + 5) & 0x20) == 0) {
+#if !defined(PREKERNEL)
         Processor::wait_check();
+#else
+        ;
+#endif
+    }
 
     if (ch == '\n' && !was_cr)
         IO::out8(serial_com1_io_port, '\r');

Kernel/Prekernel/Assertions.cpp

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2024, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Prekernel/DebugOutput.h>
+
+void __assertion_failed(char const* msg, char const* file, unsigned line, char const* func)
+{
+    write_debug_output("ASSERTION FAILED: {}\n", msg);
+    write_debug_output("{}:{} in {}\n", file, line, func);
+    halt();
+}

Kernel/Prekernel/CMakeLists.txt

@@ -1,14 +1,26 @@
 set(SOURCES
+    ../../AK/StringBuilder.cpp
+    ../../AK/StringUtils.cpp
+    ../../AK/StringView.cpp
+    ../../AK/Format.cpp
     UBSanitizer.cpp
     ../Library/MiniStdLib.cpp
+    Assertions.cpp
     boot.S
     multiboot.S
     init.cpp
+    DebugOutput.cpp
     kmalloc.cpp
     Runtime.cpp
     ../../Userland/Libraries/LibELF/Relocation.cpp
     )
 
+if ("${SERENITY_ARCH}" STREQUAL "x86_64")
+    set(SOURCES
+        ${SOURCES}
+        ../Arch/x86_64/DebugOutput.cpp)
+endif()
+
 if ("${SERENITY_ARCH}" STREQUAL "x86_64")
     set(PREKERNEL_TARGET kernel_x86-64)
 elseif("${SERENITY_ARCH}" STREQUAL "aarch64")
@@ -23,6 +35,8 @@ set_property(TARGET KernelObject PROPERTY
     IMPORTED_OBJECTS ${CMAKE_CURRENT_BINARY_DIR}/../Kernel.o
 )
 
+add_compile_definitions(PREKERNEL)
+
 add_executable(${PREKERNEL_TARGET} ${SOURCES} $<TARGET_OBJECTS:KernelObject>)
 add_dependencies(${PREKERNEL_TARGET} Kernel)
 add_dependencies(${PREKERNEL_TARGET} install_libc_headers)

Kernel/Prekernel/DebugOutput.cpp

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2024, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Platform.h>
+#include <AK/kstdio.h>
+#include <Kernel/Arch/DebugOutput.h>
+#include <Kernel/Prekernel/DebugOutput.h>
+#if ARCH(X86_64)
+#    include <Kernel/Arch/x86_64/BochsDebugOutput.h>
+#endif
+
+void debug_write_string(StringView str)
+{
+    if (str.is_null())
+        return;
+    for (u8 ch : str.bytes()) {
+        Kernel::debug_output(ch);
+#if ARCH(X86_64)
+        Kernel::bochs_debug_output(ch);
+#endif
+    }
+}
+
+extern "C" void dbgputstr(char const* characters, size_t length)
+{
+    if (!characters)
+        return;
+    debug_write_string(StringView { characters, length });
+}

Kernel/Prekernel/DebugOutput.h

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2024, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/CheckedFormatString.h>
+#include <AK/FixedStringBuffer.h>
+#include <AK/Format.h>
+#include <AK/kmalloc.h>
+#include <Kernel/Prekernel/Runtime.h>
+
+void debug_write_string(StringView str);
+
+template<typename... Parameters>
+void write_debug_output(CheckedFormatString<Parameters...>&& fmtstr, Parameters const&... parameters)
+{
+    AK::VariadicFormatParams<AK::AllowDebugOnlyFormatters::No, Parameters...> variadic_format_parameters { parameters... };
+    auto message_buffer_or_error = FixedStringBuffer<128>::vformatted(fmtstr.view(), variadic_format_parameters);
+    if (message_buffer_or_error.is_error()) {
+        debug_write_string("PANIC: Failed to write message buffer:\n"sv);
+        debug_write_string(fmtstr.view());
+        halt();
+    }
+
+    auto message_buffer = message_buffer_or_error.release_value();
+    debug_write_string(message_buffer.representable_view());
+}

Kernel/Prekernel/init.cpp

@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2021, Gunnar Beutner <gbeutner@serenityos.org>
- * Copyright (c) 2021, Liav A. <liavalb@hotmail.co.il>
+ * Copyright (c) 2021-2024, Liav A. <liavalb@hotmail.co.il>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -10,6 +10,7 @@
 #include <Kernel/Boot/Multiboot.h>
 #include <Kernel/Memory/PhysicalAddress.h>
 #include <Kernel/Memory/VirtualAddress.h>
+#include <Kernel/Prekernel/DebugOutput.h>
 #include <Kernel/Prekernel/Prekernel.h>
 #include <Kernel/Prekernel/Runtime.h>
 #include <LibELF/ELFABI.h>
@@ -54,11 +55,6 @@ void __stack_chk_fail()
     halt();
 }
 
-void __assertion_failed(char const*, char const*, unsigned int, char const*)
-{
-    halt();
-}
-
 namespace Kernel {
 
 // boot.S expects these functions to exactly have the following signatures.
@@ -96,8 +92,7 @@ extern "C" [[noreturn]] void init()
         // We only consider the first specified multiboot module, and ignore
         // the rest of the modules.
         multiboot_module_entry_t* initrd_module = (multiboot_module_entry_t*)(FlatPtr)multiboot_info_ptr->mods_addr;
-        if (initrd_module->start > initrd_module->end)
-            halt();
+        VERIFY(initrd_module->start < initrd_module->end);
 
         initrd_module_start = initrd_module->start;
         initrd_module_end = initrd_module->end;
@@ -107,8 +102,7 @@ extern "C" [[noreturn]] void init()
     // copy the ELF header and program headers because we might end up overwriting them
     Elf_Ehdr kernel_elf_header = *(Elf_Ehdr*)kernel_image;
     Elf_Phdr kernel_program_headers[16];
-    if (kernel_elf_header.e_phnum > array_size(kernel_program_headers))
-        halt();
+    VERIFY(kernel_elf_header.e_phnum < array_size(kernel_program_headers));
     __builtin_memcpy(kernel_program_headers, kernel_image + kernel_elf_header.e_phoff, sizeof(Elf_Phdr) * kernel_elf_header.e_phnum);
 
     FlatPtr kernel_physical_base = (FlatPtr)0x200000;
@@ -136,10 +130,8 @@ extern "C" [[noreturn]] void init()
             continue;
         auto start = kernel_load_base + kernel_program_header.p_vaddr;
         auto end = start + kernel_program_header.p_memsz;
-        if (start < (FlatPtr)end_of_prekernel_image)
-            halt();
-        if (kernel_physical_base + kernel_program_header.p_paddr < (FlatPtr)end_of_prekernel_image)
-            halt();
+        VERIFY(start > (FlatPtr)end_of_prekernel_image);
+        VERIFY(kernel_physical_base + kernel_program_header.p_paddr > (FlatPtr)end_of_prekernel_image);
         if (end > kernel_load_end)
             kernel_load_end = end;
     }