UserspaceEmulator: Implement a proper VM allocator

This patch brings Kernel::RangeAllocator to UserspaceEmulator in a
slightly simplified form.

It supports the basic three allocation types needed by virt$mmap():
allocate_anywhere, allocate_specific, and allocate_randomized.

Porting virt$mmap() and virt$munmap() to use the allocator makes
UE work correctly once again. :^)

10 files changed, 438 insertions, 36 deletions

diff --git a/Userland/DevTools/UserspaceEmulator/CMakeLists.txt b/Userland/DevTools/UserspaceEmulator/CMakeLists.txt
index 43164b0d6d..5068bdd56e 100644
--- a/Userland/DevTools/UserspaceEmulator/CMakeLists.txt
+++ b/Userland/DevTools/UserspaceEmulator/CMakeLists.txt
@@ -2,6 +2,8 @@ set(SOURCES
     Emulator.cpp
     MallocTracer.cpp
     MmapRegion.cpp
+    Range.cpp
+    RangeAllocator.cpp
     Region.cpp
     SimpleRegion.cpp
     SoftCPU.cpp
diff --git a/Userland/DevTools/UserspaceEmulator/Emulator.cpp b/Userland/DevTools/UserspaceEmulator/Emulator.cpp
index b19457e8bd..59e4730bad 100644
--- a/Userland/DevTools/UserspaceEmulator/Emulator.cpp
+++ b/Userland/DevTools/UserspaceEmulator/Emulator.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -32,6 +32,7 @@
 #include <AK/Format.h>
 #include <AK/LexicalPath.h>
 #include <AK/MappedFile.h>
+#include <AK/Random.h>
 #include <LibELF/AuxiliaryVector.h>
 #include <LibELF/Image.h>
 #include <LibELF/Validation.h>
@@ -81,6 +82,19 @@ Emulator::Emulator(const String& executable_path, const Vector<String>& argument
     , m_cpu(*this)
 {
     m_malloc_tracer = make<MallocTracer>(*this);
+
+    static constexpr FlatPtr userspace_range_base = 0x00800000;
+    static constexpr FlatPtr userspace_range_ceiling = 0xbe000000;
+#ifdef UE_ASLR
+    static constexpr FlatPtr page_mask = 0xfffff000u;
+    size_t random_offset = (AK::get_random<u8>() % 32 * MiB) & page_mask;
+    FlatPtr base = userspace_range_base + random_offset;
+#else
+    FlatPtr base = userspace_range_base;
+#endif
+
+    m_range_allocator.initialize_with_range(VirtualAddress(base), userspace_range_ceiling - base);
+
     ASSERT(!s_the);
     s_the = this;
     // setup_stack(arguments, environment);
@@ -972,41 +986,31 @@ u32 Emulator::virt$munmap(FlatPtr address, u32 size)
     ASSERT(region);
     if (region->size() != round_up_to_power_of_two(size, PAGE_SIZE))
         TODO();
+    m_range_allocator.deallocate(region->range());
     mmu().remove_region(*region);
     return 0;
 }
 
-FlatPtr Emulator::allocate_vm(size_t size, size_t alignment)
-{
-    // FIXME: Write a proper VM allocator
-    static FlatPtr next_address = 0x30000000;
-
-    FlatPtr final_address;
-
-    if (!alignment)
-        alignment = PAGE_SIZE;
-
-    // FIXME: What if alignment is not a power of 2?
-    final_address = round_up_to_power_of_two(next_address, alignment);
-    next_address = round_up_to_power_of_two(final_address + size, PAGE_SIZE);
-    return final_address;
-}
-
 u32 Emulator::virt$mmap(u32 params_addr)
 {
     Syscall::SC_mmap_params params;
     mmu().copy_from_vm(&params, params_addr, sizeof(params));
 
-    u32 final_size = round_up_to_power_of_two(params.size, PAGE_SIZE);
-    u32 final_address = allocate_vm(final_size, params.alignment);
-    if (params.addr != 0) {
-        // NOTE: We currently do not support allocating VM at a requeted address in the emulator.
-        // The loader needs this functionality to load .data just after .text.
-        // Luckily, since the loader calls mmap for .data right after it calls mmap for .text,
-        // the emulator will allocate a chunk of memory that is just after what we allocated for .text
-        // because of the way we currently allocate VM.
-        ASSERT(params.addr == final_address);
+    u32 requested_size = round_up_to_power_of_two(params.size, PAGE_SIZE);
+    FlatPtr final_address;
+
+    Optional<Range> result;
+    if (params.flags & MAP_RANDOMIZED) {
+        result = m_range_allocator.allocate_randomized(requested_size, params.alignment);
+    } else if (params.flags & MAP_FIXED) {
+        result = m_range_allocator.allocate_specific(VirtualAddress { params.addr }, requested_size);
+    } else {
+        result = m_range_allocator.allocate_anywhere(requested_size, params.alignment);
     }
+    if (!result.has_value())
+        return -ENOMEM;
+    final_address = result.value().base().get();
+    auto final_size = result.value().size();
 
     if (params.flags & MAP_ANONYMOUS)
         mmu().add_region(MmapRegion::create_anonymous(final_address, final_size, params.prot));
diff --git a/Userland/DevTools/UserspaceEmulator/Emulator.h b/Userland/DevTools/UserspaceEmulator/Emulator.h
index 03e051028f..caaf32e391 100644
--- a/Userland/DevTools/UserspaceEmulator/Emulator.h
+++ b/Userland/DevTools/UserspaceEmulator/Emulator.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -27,6 +27,7 @@
 #pragma once
 
 #include "MallocTracer.h"
+#include "RangeAllocator.h"
 #include "Report.h"
 #include "SoftCPU.h"
 #include "SoftMMU.h"
@@ -174,7 +175,6 @@ private:
     int virt$sendfd(int, int);
     int virt$msyscall(FlatPtr);
 
-    FlatPtr allocate_vm(size_t size, size_t alignment);
     bool find_malloc_symbols(const MmapRegion& libc_text);
 
     void dispatch_one_pending_signal();
@@ -213,6 +213,8 @@ private:
     };
 
     HashMap<String, CachedELF> m_dynamic_library_cache;
+
+    RangeAllocator m_range_allocator;
 };
 
 ALWAYS_INLINE bool Emulator::is_in_malloc_or_free() const
diff --git a/Userland/DevTools/UserspaceEmulator/MmapRegion.h b/Userland/DevTools/UserspaceEmulator/MmapRegion.h
index 75a42340ab..47fb8e0ec7 100644
--- a/Userland/DevTools/UserspaceEmulator/MmapRegion.h
+++ b/Userland/DevTools/UserspaceEmulator/MmapRegion.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
diff --git a/Userland/DevTools/UserspaceEmulator/Range.cpp b/Userland/DevTools/UserspaceEmulator/Range.cpp
new file mode 100644
index 0000000000..af6b09d19d
--- /dev/null
+++ b/Userland/DevTools/UserspaceEmulator/Range.cpp
@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Range.h"
+#include <AK/Vector.h>
+
+namespace UserspaceEmulator {
+
+Vector<Range, 2> Range::carve(const Range& taken)
+{
+    ASSERT((taken.size() % PAGE_SIZE) == 0);
+    Vector<Range, 2> parts;
+    if (taken == *this)
+        return {};
+    if (taken.base() > base())
+        parts.append({ base(), taken.base().get() - base().get() });
+    if (taken.end() < end())
+        parts.append({ taken.end(), end().get() - taken.end().get() });
+    return parts;
+}
+
+}
diff --git a/Userland/DevTools/UserspaceEmulator/Range.h b/Userland/DevTools/UserspaceEmulator/Range.h
new file mode 100644
index 0000000000..08a8e9caaf
--- /dev/null
+++ b/Userland/DevTools/UserspaceEmulator/Range.h
@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+#include <Kernel/VirtualAddress.h>
+
+namespace UserspaceEmulator {
+
+class Range {
+    friend class RangeAllocator;
+
+public:
+    Range() = delete;
+    Range(VirtualAddress base, size_t size)
+        : m_base(base)
+        , m_size(size)
+    {
+    }
+
+    VirtualAddress base() const { return m_base; }
+    size_t size() const { return m_size; }
+    bool is_valid() const { return !m_base.is_null(); }
+
+    bool contains(VirtualAddress vaddr) const { return vaddr >= base() && vaddr < end(); }
+
+    VirtualAddress end() const { return m_base.offset(m_size); }
+
+    bool operator==(const Range& other) const
+    {
+        return m_base == other.m_base && m_size == other.m_size;
+    }
+
+    bool contains(VirtualAddress base, size_t size) const
+    {
+        if (base.offset(size) < base)
+            return false;
+        return base >= m_base && base.offset(size) <= end();
+    }
+
+    bool contains(const Range& other) const
+    {
+        return contains(other.base(), other.size());
+    }
+
+    Vector<Range, 2> carve(const Range&);
+
+private:
+    VirtualAddress m_base;
+    size_t m_size { 0 };
+};
+
+}
+
+namespace AK {
+template<>
+struct Traits<UserspaceEmulator::Range> : public GenericTraits<UserspaceEmulator::Range> {
+    static constexpr bool is_trivial() { return true; }
+};
+}
diff --git a/Userland/DevTools/UserspaceEmulator/RangeAllocator.cpp b/Userland/DevTools/UserspaceEmulator/RangeAllocator.cpp
new file mode 100644
index 0000000000..f4f6fc1341
--- /dev/null
+++ b/Userland/DevTools/UserspaceEmulator/RangeAllocator.cpp
@@ -0,0 +1,207 @@
+/*
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "RangeAllocator.h"
+#include <AK/BinarySearch.h>
+#include <AK/Checked.h>
+#include <AK/QuickSort.h>
+#include <AK/Random.h>
+
+#define VM_GUARD_PAGES
+#define PAGE_MASK ((FlatPtr)0xfffff000u)
+
+namespace UserspaceEmulator {
+
+RangeAllocator::RangeAllocator()
+    : m_total_range({}, 0)
+{
+}
+
+void RangeAllocator::initialize_with_range(VirtualAddress base, size_t size)
+{
+    m_total_range = { base, size };
+    m_available_ranges.append({ base, size });
+}
+
+RangeAllocator::~RangeAllocator()
+{
+}
+
+void RangeAllocator::dump() const
+{
+    dbgln("RangeAllocator({})", this);
+    for (auto& range : m_available_ranges) {
+        dbgln("    {:x} -> {:x}", range.base().get(), range.end().get() - 1);
+    }
+}
+
+void RangeAllocator::carve_at_index(int index, const Range& range)
+{
+    auto remaining_parts = m_available_ranges[index].carve(range);
+    ASSERT(remaining_parts.size() >= 1);
+    ASSERT(m_total_range.contains(remaining_parts[0]));
+    m_available_ranges[index] = remaining_parts[0];
+    if (remaining_parts.size() == 2) {
+        ASSERT(m_total_range.contains(remaining_parts[1]));
+        m_available_ranges.insert(index + 1, move(remaining_parts[1]));
+    }
+}
+
+Optional<Range> RangeAllocator::allocate_randomized(size_t size, size_t alignment)
+{
+    if (!size)
+        return {};
+
+    ASSERT((size % PAGE_SIZE) == 0);
+    ASSERT((alignment % PAGE_SIZE) == 0);
+
+    // FIXME: I'm sure there's a smarter way to do this.
+    static constexpr size_t maximum_randomization_attempts = 1000;
+    for (size_t i = 0; i < maximum_randomization_attempts; ++i) {
+        VirtualAddress random_address { AK::get_random<FlatPtr>() };
+        random_address.mask(PAGE_MASK);
+
+        if (!m_total_range.contains(random_address, size))
+            continue;
+
+        auto range = allocate_specific(random_address, size);
+        if (range.has_value())
+            return range;
+    }
+
+    return allocate_anywhere(size, alignment);
+}
+
+Optional<Range> RangeAllocator::allocate_anywhere(size_t size, size_t alignment)
+{
+    if (!size)
+        return {};
+
+    ASSERT((size % PAGE_SIZE) == 0);
+    ASSERT((alignment % PAGE_SIZE) == 0);
+
+#ifdef VM_GUARD_PAGES
+    // NOTE: We pad VM allocations with a guard page on each side.
+    if (Checked<size_t>::addition_would_overflow(size, PAGE_SIZE * 2))
+        return {};
+
+    size_t effective_size = size + PAGE_SIZE * 2;
+    size_t offset_from_effective_base = PAGE_SIZE;
+#else
+    size_t effective_size = size;
+    size_t offset_from_effective_base = 0;
+#endif
+
+    if (Checked<size_t>::addition_would_overflow(effective_size, alignment))
+        return {};
+
+    for (size_t i = 0; i < m_available_ranges.size(); ++i) {
+        auto& available_range = m_available_ranges[i];
+        // FIXME: This check is probably excluding some valid candidates when using a large alignment.
+        if (available_range.size() < (effective_size + alignment))
+            continue;
+
+        FlatPtr initial_base = available_range.base().offset(offset_from_effective_base).get();
+        FlatPtr aligned_base = round_up_to_power_of_two(initial_base, alignment);
+
+        Range allocated_range(VirtualAddress(aligned_base), size);
+        ASSERT(m_total_range.contains(allocated_range));
+
+        if (available_range == allocated_range) {
+            m_available_ranges.remove(i);
+            return allocated_range;
+        }
+        carve_at_index(i, allocated_range);
+        return allocated_range;
+    }
+    klog() << "RangeAllocator: Failed to allocate anywhere: " << size << ", " << alignment;
+    return {};
+}
+
+Optional<Range> RangeAllocator::allocate_specific(VirtualAddress base, size_t size)
+{
+    if (!size)
+        return {};
+
+    ASSERT(base.is_page_aligned());
+    ASSERT((size % PAGE_SIZE) == 0);
+
+    Range allocated_range(base, size);
+    for (size_t i = 0; i < m_available_ranges.size(); ++i) {
+        auto& available_range = m_available_ranges[i];
+        ASSERT(m_total_range.contains(allocated_range));
+        if (!available_range.contains(base, size))
+            continue;
+        if (available_range == allocated_range) {
+            m_available_ranges.remove(i);
+            return allocated_range;
+        }
+        carve_at_index(i, allocated_range);
+        return allocated_range;
+    }
+    return {};
+}
+
+void RangeAllocator::deallocate(const Range& range)
+{
+    ASSERT(m_total_range.contains(range));
+    ASSERT(range.size());
+    ASSERT((range.size() % PAGE_SIZE) == 0);
+    ASSERT(range.base() < range.end());
+    ASSERT(!m_available_ranges.is_empty());
+
+    size_t nearby_index = 0;
+    auto* existing_range = binary_search(
+        m_available_ranges.span(),
+        range,
+        &nearby_index,
+        [](auto& a, auto& b) { return a.base().get() - b.end().get(); });
+
+    size_t inserted_index = 0;
+    if (existing_range) {
+        existing_range->m_size += range.size();
+        inserted_index = nearby_index;
+    } else {
+        m_available_ranges.insert_before_matching(
+            Range(range), [&](auto& entry) {
+                return entry.base() >= range.end();
+            },
+            nearby_index, &inserted_index);
+    }
+
+    if (inserted_index < (m_available_ranges.size() - 1)) {
+        // We already merged with previous. Try to merge with next.
+        auto& inserted_range = m_available_ranges[inserted_index];
+        auto& next_range = m_available_ranges[inserted_index + 1];
+        if (inserted_range.end() == next_range.base()) {
+            inserted_range.m_size += next_range.size();
+            m_available_ranges.remove(inserted_index + 1);
+            return;
+        }
+    }
+}
+
+}
diff --git a/Userland/DevTools/UserspaceEmulator/RangeAllocator.h b/Userland/DevTools/UserspaceEmulator/RangeAllocator.h
new file mode 100644
index 0000000000..5619dc52d9
--- /dev/null
+++ b/Userland/DevTools/UserspaceEmulator/RangeAllocator.h
@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Range.h"
+#include <AK/Vector.h>
+
+namespace UserspaceEmulator {
+
+class RangeAllocator {
+public:
+    RangeAllocator();
+    ~RangeAllocator();
+
+    void initialize_with_range(VirtualAddress, size_t);
+
+    Optional<Range> allocate_anywhere(size_t, size_t alignment = PAGE_SIZE);
+    Optional<Range> allocate_specific(VirtualAddress, size_t);
+    Optional<Range> allocate_randomized(size_t, size_t alignment);
+    void deallocate(const Range&);
+
+    void dump() const;
+
+    bool contains(const Range& range) const { return m_total_range.contains(range); }
+
+private:
+    void carve_at_index(int, const Range&);
+
+    Vector<Range> m_available_ranges;
+    Range m_total_range;
+};
+
+}
diff --git a/Userland/DevTools/UserspaceEmulator/Region.cpp b/Userland/DevTools/UserspaceEmulator/Region.cpp
index c5f989c802..54c145a2a7 100644
--- a/Userland/DevTools/UserspaceEmulator/Region.cpp
+++ b/Userland/DevTools/UserspaceEmulator/Region.cpp
@@ -31,8 +31,7 @@ namespace UserspaceEmulator {
 
 Region::Region(u32 base, u32 size)
     : m_emulator(Emulator::the())
-    , m_base(base)
-    , m_size(size)
+    , m_range(Range { VirtualAddress { base }, size })
 {
 }
 
diff --git a/Userland/DevTools/UserspaceEmulator/Region.h b/Userland/DevTools/UserspaceEmulator/Region.h
index ffb15cf941..589f7b77a7 100644
--- a/Userland/DevTools/UserspaceEmulator/Region.h
+++ b/Userland/DevTools/UserspaceEmulator/Region.h
@@ -26,6 +26,7 @@
 
 #pragma once
 
+#include "Range.h"
 #include "ValueWithShadow.h"
 #include <AK/TypeCasts.h>
 #include <AK/Types.h>
@@ -38,9 +39,11 @@ class Region {
 public:
     virtual ~Region() { }
 
-    u32 base() const { return m_base; }
-    u32 size() const { return m_size; }
-    u32 end() const { return m_base + m_size; }
+    const Range& range() const { return m_range; }
+
+    u32 base() const { return m_range.base().get(); }
+    u32 size() const { return m_range.size(); }
+    u32 end() const { return m_range.end().get(); }
 
     bool contains(u32 address) const { return address >= base() && address < end(); }
 
@@ -82,8 +85,7 @@ protected:
 private:
     Emulator& m_emulator;
 
-    u32 m_base { 0 };
-    u32 m_size { 0 };
+    Range m_range;
 
     bool m_stack { false };
     bool m_text { false };