From 27860cfaa2dd36389c79eddf31e78c6668cc9070 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=B6nke=20Holz?= <sholz8530@gmail.com>
Date: Wed, 3 Jan 2024 17:21:19 +0100
Subject: [PATCH] Kernel/riscv64: Add a basic trap handler to `pre_init`

This trap handler uses the SBI to print an error message via a newly
introduced panic function, which is necessary as `pre_init` is running
identity mapped.
Also add a header file for `pre_init.cpp` as we wan't to use the panic
and `dbgln` function in the MMU init code as well.
---
 Kernel/Arch/riscv64/pre_init.cpp | 42 +++++++++++++++++++++++++++++---
 Kernel/Arch/riscv64/pre_init.h   | 22 +++++++++++++++++
 2 files changed, 60 insertions(+), 4 deletions(-)
 create mode 100644 Kernel/Arch/riscv64/pre_init.h

diff --git a/Kernel/Arch/riscv64/pre_init.cpp b/Kernel/Arch/riscv64/pre_init.cpp
index 3bbbd7d99f..1f277ad051 100644
--- a/Kernel/Arch/riscv64/pre_init.cpp
+++ b/Kernel/Arch/riscv64/pre_init.cpp
@@ -4,19 +4,53 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/Types.h>
+#include <Kernel/Arch/riscv64/pre_init.h>
 
 #include <Kernel/Arch/Processor.h>
-#include <Kernel/Memory/PhysicalAddress.h>
+#include <Kernel/Arch/riscv64/MMU.h>
+#include <Kernel/Arch/riscv64/SBI.h>
+#include <Kernel/Sections.h>
 
 namespace Kernel {
 
-extern "C" [[noreturn]] void pre_init(FlatPtr mhartid, PhysicalPtr fdt_phys_addr);
-extern "C" [[noreturn]] void pre_init(FlatPtr mhartid, PhysicalPtr fdt_phys_addr)
+UNMAP_AFTER_INIT void dbgln_without_mmu(StringView message)
+{
+    auto probe_result = SBI::Base::probe_extension(SBI::EID::DebugConsole);
+    if (probe_result.is_error() || probe_result.value() == 0) {
+        for (auto const ch : message.bytes())
+            (void)SBI::Legacy::console_putchar(ch);
+        (void)SBI::Legacy::console_putchar('\n');
+    } else {
+        for (auto const ch : message.bytes())
+            (void)SBI::DBCN::debug_console_write_byte(ch);
+        (void)SBI::DBCN::debug_console_write_byte('\n');
+    }
+}
+
+[[noreturn]] UNMAP_AFTER_INIT void panic_without_mmu(StringView message)
+{
+    dbgln_without_mmu("KERNEL PANIC in pre_init :^("sv);
+    dbgln_without_mmu(message);
+
+    // We can't use Processor::halt() here, as that would result in an absolute jump.
+    RISCV64::CSR::write(RISCV64::CSR::Address::SIE, 0);
+    for (;;)
+        asm volatile("wfi");
+}
+
+[[gnu::aligned(4)]] [[noreturn]] UNMAP_AFTER_INIT static void early_trap_handler()
+{
+    panic_without_mmu("Unexpected trap"sv);
+}
+
+extern "C" [[noreturn]] UNMAP_AFTER_INIT void pre_init(FlatPtr mhartid, PhysicalPtr fdt_phys_addr)
 {
     (void)mhartid;
     (void)fdt_phys_addr;
 
+    // Catch traps in pre_init
+    RISCV64::CSR::write(RISCV64::CSR::Address::STVEC, bit_cast<FlatPtr>(&early_trap_handler));
+
     // FIXME: Implement this
 
     Processor::halt();
diff --git a/Kernel/Arch/riscv64/pre_init.h b/Kernel/Arch/riscv64/pre_init.h
new file mode 100644
index 0000000000..d304c85a3d
--- /dev/null
+++ b/Kernel/Arch/riscv64/pre_init.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2023, Sönke Holz <sholz8530@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Forward.h>
+#include <Kernel/Memory/PhysicalAddress.h>
+
+#include <AK/Platform.h>
+VALIDATE_IS_RISCV64()
+
+namespace Kernel {
+
+void dbgln_without_mmu(StringView);
+[[noreturn]] void panic_without_mmu(StringView);
+
+extern "C" [[noreturn]] void pre_init(FlatPtr mhartid, PhysicalPtr fdt_phys_addr);
+
+}