Kernel: Show QR code with panic logs on kernel panic

This makes debugging on real hardware easier!

kernel/CMakeLists.txt

@@ -165,6 +165,12 @@ set(KLIBC_SOURCES
 	../userspace/libraries/LibC/arch/${BANAN_ARCH}/string.S
 )
 
+set(LIBDEFLATE_SOURCE
+	../userspace/libraries/LibDEFLATE/Compressor.cpp
+	../userspace/libraries/LibDEFLATE/Decompressor.cpp
+	../userspace/libraries/LibDEFLATE/HuffmanTree.cpp
+)
+
 set(LIBFONT_SOURCES
 	../userspace/libraries/LibFont/Font.cpp
 	../userspace/libraries/LibFont/PSF.cpp
@@ -175,18 +181,25 @@ set(LIBINPUT_SOURCE
 	../userspace/libraries/LibInput/KeyEvent.cpp
 )
 
+set(LIBQR_SOURCE
+	../userspace/libraries/LibQR/QRCode.cpp
+)
+
 set(KERNEL_SOURCES
 	${KERNEL_SOURCES}
 	${BAN_SOURCES}
 	${KLIBC_SOURCES}
+	${LIBDEFLATE_SOURCE}
 	${LIBFONT_SOURCES}
 	${LIBINPUT_SOURCE}
+	${LIBQR_SOURCE}
 )
 
 add_executable(kernel ${KERNEL_SOURCES})
 
 target_compile_definitions(kernel PRIVATE __is_kernel)
 target_compile_definitions(kernel PRIVATE __arch=${BANAN_ARCH})
+target_compile_definitions(kernel PRIVATE LIBDEFLATE_AVOID_STACK=1)
 
 target_compile_options(kernel PRIVATE
 	-O2 -g
@@ -240,9 +253,11 @@ add_custom_command(
 
 banan_include_headers(kernel ban)
 banan_include_headers(kernel libc)
-banan_include_headers(kernel libfont)
+banan_include_headers(kernel libdeflate)
 banan_include_headers(kernel libelf)
+banan_include_headers(kernel libfont)
 banan_include_headers(kernel libinput)
+banan_include_headers(kernel libqr)
 
 banan_install_headers(kernel)
 set_target_properties(kernel PROPERTIES OUTPUT_NAME banan-os.kernel)

kernel/include/kernel/Debug.h

@@ -74,6 +74,8 @@
 namespace Debug
 {
 	void dump_stack_trace();
+	void dump_qr_code();
+
 	void putchar(char);
 	void print_prefix(const char*, int);
 

kernel/include/kernel/Panic.h

@@ -19,15 +19,26 @@ namespace Kernel
 		asm volatile("cli");
 
 		const bool had_debug_lock = Debug::s_debug_lock.current_processor_has_lock();
+
+		bool first_panic = false;
+
+		{
+			SpinLockGuard _(Debug::s_debug_lock);
 			derrorln("Kernel panic at {}", location);
 			if (had_debug_lock)
 				derrorln("  while having debug lock...");
 			derrorln(message, BAN::forward<Args>(args)...);
 			if (!g_paniced)
 			{
-			g_paniced = true;
 				Debug::dump_stack_trace();
+				g_paniced = true;
+				first_panic = true;
 			}
+		}
+
+		if (first_panic)
+			Debug::dump_qr_code();
+
 		asm volatile("ud2");
 		__builtin_unreachable();
 	}

kernel/kernel/Debug.cpp

@@ -1,4 +1,5 @@
 #include <kernel/Debug.h>
+#include <kernel/Device/FramebufferDevice.h>
 #include <kernel/InterruptController.h>
 #include <kernel/Lock/SpinLock.h>
 #include <kernel/Memory/PageTable.h>
@@ -6,6 +7,9 @@
 #include <kernel/Terminal/TTY.h>
 #include <kernel/Timer/Timer.h>
 
+#include <LibDEFLATE/Compressor.h>
+#include <LibQR/QRCode.h>
+
 #include <ctype.h>
 
 bool g_disable_debug = false;
@@ -15,6 +19,15 @@ namespace Debug
 
 	Kernel::RecursiveSpinLock s_debug_lock;
 
+	static constexpr char s_panic_url_prefix[] = "https://bananymous.com/panic#";
+	static constexpr size_t s_qr_code_max_capacity { 2953 };
+	static bool s_qr_code_shown { false };
+
+	static char s_debug_buffer[16 * 1024] {};
+	static size_t s_debug_buffer_tail { 0 };
+	static size_t s_debug_buffer_size { 0 };
+	static uint8_t s_debug_ansi_state { 0 };
+
 	void dump_stack_trace()
 	{
 		using namespace Kernel;
@@ -72,17 +85,203 @@ namespace Debug
 		BAN::Formatter::print(Debug::putchar, "\e[m");
 	}
 
+	static void queue_debug_buffer(char ch)
+	{
+		switch (s_debug_ansi_state)
+		{
+			case 1:
+				if (ch == '[')
+				{
+					s_debug_ansi_state = 2;
+					break;
+				}
+				s_debug_ansi_state = 0;
+				[[fallthrough]];
+			case 0:
+				if (ch == '\e')
+				{
+					s_debug_ansi_state = 1;
+					break;
+				}
+				if (!isprint(ch) && ch != '\n')
+					break;
+				s_debug_buffer[(s_debug_buffer_tail + s_debug_buffer_size) % sizeof(s_debug_buffer)] = ch;
+				if (s_debug_buffer_size < sizeof(s_debug_buffer))
+					s_debug_buffer_size++;
+				else
+					s_debug_buffer_tail = (s_debug_buffer_tail + 1) % sizeof(s_debug_buffer);
+				break;
+			case 2:
+				if (isalpha(ch))
+					s_debug_ansi_state = 0;
+				break;
+		}
+	}
+
+	static void reverse(char* first, char* last)
+	{
+		const size_t len = last - first;
+		for (size_t i = 0; i < len / 2; i++)
+			BAN::swap(first[i], first[len - i - 1]);
+	}
+
+	static void rotate(char* first, char* middle, char* last)
+	{
+		reverse(first, middle);
+		reverse(middle, last);
+		reverse(first, last);
+	}
+
+	static BAN::ErrorOr<BAN::Vector<uint8_t>> compress_kernel_logs()
+	{
+		constexpr size_t max_size = ((s_qr_code_max_capacity + 3) / 4 * 3) - sizeof(s_panic_url_prefix);
+
+		BAN::Vector<uint8_t> result;
+
+		size_t l = 0, r = s_debug_buffer_size;
+		while (l + 50 < r)
+		{
+			const size_t middle = (l + r) / 2;
+			const uint8_t* base = reinterpret_cast<const uint8_t*>(s_debug_buffer) + s_debug_buffer_size - middle;
+
+			auto compressed = TRY(LibDEFLATE::Compressor({ base, middle }, LibDEFLATE::StreamType::Zlib).compress());
+			if (compressed.size() > max_size)
+				r = middle;
+			else
+			{
+				l = middle;
+				result = BAN::move(compressed);
+			}
+		}
+
+		return result;
+	}
+
+	void dump_qr_code()
+	{
+		ASSERT(Kernel::g_paniced);
+
+		auto boot_framebuffer = Kernel::FramebufferDevice::boot_framebuffer();
+		if (!boot_framebuffer)
+		{
+			derrorln("No boot framebuffer, not generating QR code");
+			return;
+		}
+		if (boot_framebuffer->width() < 177 + 8 || boot_framebuffer->height() < 177 + 8)
+		{
+			derrorln("Boot framebuffer is too small for a qr code");
+			return;
+		}
+
+		// rotate logs to start from index 0 and be contiguous
+		rotate(s_debug_buffer, s_debug_buffer + s_debug_buffer_tail, s_debug_buffer + sizeof(s_debug_buffer));
+
+		auto compressed_or_error = compress_kernel_logs();
+		if (compressed_or_error.is_error())
+		{
+			// TODO: send uncompressed logs?
+			derrorln("Failed to compress kernel logs: {}", compressed_or_error.error());
+			return;
+		}
+
+		auto compressed = compressed_or_error.release_value();
+
+		static uint8_t qr_code_data[s_qr_code_max_capacity];
+		size_t qr_code_data_len = 0;
+
+		for (size_t i = 0; s_panic_url_prefix[i]; i++)
+			qr_code_data[qr_code_data_len++] = s_panic_url_prefix[i];
+
+		constexpr char alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+		for (size_t i = 0; i < compressed.size() / 3; i++)
+		{
+			const uint32_t bits =
+				((compressed[3 * i + 0]) << 16) |
+				((compressed[3 * i + 1]) <<  8) |
+				((compressed[3 * i + 2]) <<  0);
+
+			qr_code_data[qr_code_data_len++] = alphabet[(bits >> 18) & 0x3F];
+			qr_code_data[qr_code_data_len++] = alphabet[(bits >> 12) & 0x3F];
+			qr_code_data[qr_code_data_len++] = alphabet[(bits >>  6) & 0x3F];
+			qr_code_data[qr_code_data_len++] = alphabet[(bits >>  0) & 0x3F];
+		}
+
+		switch (compressed.size() % 3)
+		{
+			case 0:
+				break;
+			case 1:
+			{
+				const uint16_t bits =
+					(compressed[compressed.size() - 1] << 4);
+				qr_code_data[qr_code_data_len++] = alphabet[(bits >>  6) & 0x3F];
+				qr_code_data[qr_code_data_len++] = alphabet[(bits >>  0) & 0x3F];
+				break;
+			}
+			case 2:
+			{
+				const uint32_t bits =
+					(compressed[compressed.size() - 2] << 10) |
+					(compressed[compressed.size() - 1] <<  2);
+				qr_code_data[qr_code_data_len++] = alphabet[(bits >> 12) & 0x3F];
+				qr_code_data[qr_code_data_len++] = alphabet[(bits >>  6) & 0x3F];
+				qr_code_data[qr_code_data_len++] = alphabet[(bits >>  0) & 0x3F];
+				break;
+			}
+		}
+
+		auto qr_or_error = LibQR::QRCode::generate({ qr_code_data, qr_code_data_len });
+		if (qr_or_error.is_error())
+		{
+			derrorln("Failed to generate QR code");
+			return;
+		}
+
+		auto qr_code = qr_or_error.release_value();
+
+		// after this point no more logs are printed to framebuffer
+		s_qr_code_shown = true;
+
+		const size_t min_framebuffer_dimension = BAN::Math::min(boot_framebuffer->width(), boot_framebuffer->height());
+		const size_t module_size = min_framebuffer_dimension / (qr_code.size() + 8);
+
+		for (size_t y = 0; y < (qr_code.size() + 8) * module_size; y++)
+			for (size_t x = 0; x < (qr_code.size() + 8) * module_size; x++)
+				boot_framebuffer->set_pixel(x, y, 0xFFFFFF);
+
+		for (size_t y = 0; y < qr_code.size(); y++)
+		{
+			for (size_t x = 0; x < qr_code.size(); x++)
+			{
+				if (!qr_code.get(x, y))
+					continue;
+				for (size_t i = 0; i < module_size; i++)
+					for (size_t j = 0; j < module_size; j++)
+						boot_framebuffer->set_pixel((x + 4) * module_size + j, (y + 4) * module_size + i, 0x000000);
+			}
+		}
+
+		boot_framebuffer->sync_pixels_rectangle(0, 0, (qr_code.size() + 8) * module_size, (qr_code.size() + 8) * module_size);
+	}
+
 	void putchar(char ch)
 	{
 		using namespace Kernel;
 
+		if (!g_paniced)
+			queue_debug_buffer(ch);
+
 		if (g_disable_debug)
 			return;
 
 		if (Kernel::Serial::has_devices())
 			return Kernel::Serial::putchar_any(ch);
 		if (Kernel::TTY::is_initialized())
+		{
+			if (s_qr_code_shown)
+				return;
 			return Kernel::TTY::putchar_current(ch);
+		}
 
 		if (g_terminal_driver)
 		{