From b6cc95c38e651025323f7b8d949eafaaf8616f28 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=B6nke=20Holz?= <sholz8530@gmail.com>
Date: Thu, 9 May 2024 22:55:54 +0200
Subject: [PATCH] AK: Add a function for frame pointer-based stack unwinding

Instead of duplicating stack unwinding code everywhere, introduce a new
AK helper to unwind the stack in a generic way.
---
 AK/StackUnwinder.h | 69 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100644 AK/StackUnwinder.h

diff --git a/AK/StackUnwinder.h b/AK/StackUnwinder.h
new file mode 100644
index 00000000000..d03d8e5c9a6
--- /dev/null
+++ b/AK/StackUnwinder.h
@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2024, Sönke Holz <sholz8530@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Concepts.h>
+#include <AK/Error.h>
+#include <AK/Types.h>
+
+namespace AK {
+
+struct StackFrame {
+    FlatPtr return_address;
+    FlatPtr previous_frame_pointer;
+};
+
+// This function only returns errors if on_stack_frame returns an error.
+// It doesn't return an error on failed memory reads, since the last frame record sometimes contains invalid addresses when using frame pointer-based unwinding.
+ErrorOr<void> unwind_stack_from_frame_pointer(FlatPtr frame_pointer, CallableAs<ErrorOr<FlatPtr>, FlatPtr> auto read_memory, CallableAs<ErrorOr<IterationDecision>, StackFrame> auto on_stack_frame)
+{
+    // aarch64/x86_64 frame record layout:
+    // fp/rbp+8: return address
+    // fp/rbp+0: previous base/frame pointer
+
+    // riscv64 frame record layout:
+    // fp-8: return address
+    // fp-16: previous frame pointer
+
+#if ARCH(AARCH64) || ARCH(X86_64)
+    static constexpr ptrdiff_t FRAME_POINTER_RETURN_ADDRESS_OFFSET = 8;
+    static constexpr ptrdiff_t FRAME_POINTER_PREVIOUS_FRAME_POINTER_OFFSET = 0;
+#elif ARCH(RISCV64)
+    static constexpr ptrdiff_t FRAME_POINTER_RETURN_ADDRESS_OFFSET = -8;
+    static constexpr ptrdiff_t FRAME_POINTER_PREVIOUS_FRAME_POINTER_OFFSET = -16;
+#else
+#    error Unknown architecture
+#endif
+
+    FlatPtr current_frame_pointer = frame_pointer;
+
+    while (current_frame_pointer != 0) {
+        StackFrame stack_frame;
+
+        auto maybe_return_address = read_memory(current_frame_pointer + FRAME_POINTER_RETURN_ADDRESS_OFFSET);
+        if (maybe_return_address.is_error())
+            return {};
+        stack_frame.return_address = maybe_return_address.value();
+
+        if (stack_frame.return_address == 0)
+            return {};
+
+        auto maybe_previous_frame_pointer = read_memory(current_frame_pointer + FRAME_POINTER_PREVIOUS_FRAME_POINTER_OFFSET);
+        if (maybe_previous_frame_pointer.is_error())
+            return {};
+        stack_frame.previous_frame_pointer = maybe_previous_frame_pointer.value();
+
+        if (TRY(on_stack_frame(stack_frame)) == IterationDecision::Break)
+            return {};
+
+        current_frame_pointer = maybe_previous_frame_pointer.value();
+    }
+
+    return {};
+}
+
+}