From 8fd97bee7fb618b758c8c9b61cdadc75feacdddb Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sat, 14 Nov 2020 23:07:07 +0100
Subject: [PATCH] UserspaceEmulator: Forget ChunkedBlocks after they are
 munmap()'ed

This is not ideal since we lose free() backtraces, but it will require
some thinking to get this right.
---
 DevTools/UserspaceEmulator/MallocTracer.cpp | 8 ++++++++
 DevTools/UserspaceEmulator/MallocTracer.h   | 3 +++
 DevTools/UserspaceEmulator/MmapRegion.cpp   | 5 +++++
 3 files changed, 16 insertions(+)

diff --git a/DevTools/UserspaceEmulator/MallocTracer.cpp b/DevTools/UserspaceEmulator/MallocTracer.cpp
index 83039adf26..9bc7aa3491 100644
--- a/DevTools/UserspaceEmulator/MallocTracer.cpp
+++ b/DevTools/UserspaceEmulator/MallocTracer.cpp
@@ -40,6 +40,14 @@ MallocTracer::MallocTracer()
 {
 }
 
+void MallocTracer::notify_malloc_block_was_released(Badge<MmapRegion>, MmapRegion& region)
+{
+    // FIXME: It's sad that we may lose a bunch of free() backtraces here,
+    //        but if the address is reused for a new ChunkedBlock, things will
+    //        get extremely confused.
+    m_chunked_blocks.remove(region.base());
+}
+
 void MallocTracer::target_did_malloc(Badge<SoftCPU>, FlatPtr address, size_t size)
 {
     auto* region = Emulator::the().mmu().find_region({ 0x20, address });
diff --git a/DevTools/UserspaceEmulator/MallocTracer.h b/DevTools/UserspaceEmulator/MallocTracer.h
index aad1d66adb..290cd58a7c 100644
--- a/DevTools/UserspaceEmulator/MallocTracer.h
+++ b/DevTools/UserspaceEmulator/MallocTracer.h
@@ -34,6 +34,7 @@
 
 namespace UserspaceEmulator {
 
+class MmapRegion;
 class SoftCPU;
 
 class MallocTracer {
@@ -44,6 +45,8 @@ public:
     void target_did_free(Badge<SoftCPU>, FlatPtr address);
     void target_did_realloc(Badge<SoftCPU>, FlatPtr address, size_t);
 
+    void notify_malloc_block_was_released(Badge<MmapRegion>, MmapRegion&);
+
     void audit_read(FlatPtr address, size_t);
     void audit_write(FlatPtr address, size_t);
 
diff --git a/DevTools/UserspaceEmulator/MmapRegion.cpp b/DevTools/UserspaceEmulator/MmapRegion.cpp
index f0036f729c..a01d837082 100644
--- a/DevTools/UserspaceEmulator/MmapRegion.cpp
+++ b/DevTools/UserspaceEmulator/MmapRegion.cpp
@@ -58,6 +58,11 @@ MmapRegion::MmapRegion(u32 base, u32 size, int prot)
 
 MmapRegion::~MmapRegion()
 {
+    if (is_malloc_block()) {
+        if (auto* tracer = Emulator::the().malloc_tracer())
+            tracer->notify_malloc_block_was_released({}, *this);
+    }
+
     free(m_shadow_data);
     if (m_file_backed)
         munmap(m_data, size());