UserspaceEmulator: Make mmap'ed memory track read/write protection

Here's the first time we get a taste of better information than the
real hardware can give us: unlike x86 CPUs, we can actually support
write-only memory, so now we do!

While this isn't immediately useful, it's still pretty cool. :^)

DevTools/UserspaceEmulator/MmapRegion.cpp

@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) 2020, 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 "MmapRegion.h"
+#include "Emulator.h"
+#include <sys/mman.h>
+
+namespace UserspaceEmulator {
+
+MmapRegion::MmapRegion(u32 base, u32 size, int prot)
+    : Region(base, size)
+    , m_prot(prot)
+{
+    m_data = (u8*)calloc(1, size);
+}
+
+MmapRegion::~MmapRegion()
+{
+    free(m_data);
+}
+
+u8 MmapRegion::read8(FlatPtr offset)
+{
+    if (!is_readable()) {
+        warn() << "8-bit read from unreadable MmapRegion @ " << (const void*)(base() + offset);
+        Emulator::the().dump_backtrace();
+        TODO();
+    }
+
+    ASSERT(offset < size());
+    return *reinterpret_cast<const u8*>(m_data + offset);
+}
+
+u16 MmapRegion::read16(u32 offset)
+{
+    if (!is_readable()) {
+        warn() << "16-bit from unreadable MmapRegion @ " << (const void*)(base() + offset);
+        Emulator::the().dump_backtrace();
+        TODO();
+    }
+
+    ASSERT(offset + 1 < size());
+    return *reinterpret_cast<const u16*>(m_data + offset);
+}
+
+u32 MmapRegion::read32(u32 offset)
+{
+    if (!is_readable()) {
+        warn() << "32-bit read from unreadable MmapRegion @ " << (const void*)(base() + offset);
+        Emulator::the().dump_backtrace();
+        TODO();
+    }
+
+    ASSERT(offset + 3 < size());
+    return *reinterpret_cast<const u32*>(m_data + offset);
+}
+
+void MmapRegion::write8(u32 offset, u8 value)
+{
+    if (!is_writable()) {
+        warn() << "8-bit write to unreadable MmapRegion @ " << (const void*)(base() + offset);
+        Emulator::the().dump_backtrace();
+        TODO();
+    }
+
+    ASSERT(offset < size());
+    *reinterpret_cast<u8*>(m_data + offset) = value;
+}
+
+void MmapRegion::write16(u32 offset, u16 value)
+{
+    if (!is_writable()) {
+        warn() << "16-bit write to unreadable MmapRegion @ " << (const void*)(base() + offset);
+        Emulator::the().dump_backtrace();
+        TODO();
+    }
+
+    ASSERT(offset + 1 < size());
+    *reinterpret_cast<u16*>(m_data + offset) = value;
+}
+
+void MmapRegion::write32(u32 offset, u32 value)
+{
+    if (!is_writable()) {
+        warn() << "32-bit write to unreadable MmapRegion @ " << (const void*)(base() + offset);
+        Emulator::the().dump_backtrace();
+        TODO();
+    }
+
+    ASSERT(offset + 3 < size());
+    *reinterpret_cast<u32*>(m_data + offset) = value;
+}
+
+}