dolphin/Source/Core/Common/CodeBlock.h

// Copyright 2014 Dolphin Emulator Project
// Licensed under GPLv2+
// Refer to the license.txt file included.

#pragma once

#include "Common/Assert.h"
#include "Common/MemoryUtil.h"
#include "Common/NonCopyable.h"

// Everything that needs to generate code should inherit from this.
// You get memory management for free, plus, you can use all emitter functions without
// having to prefix them with gen-> or something similar.
// Example implementation:
// class JIT : public CodeBlock<ARMXEmitter> {}
template<class T> class CodeBlock : public T, NonCopyable
{
private:
	// A privately used function to set the executable RAM space to something invalid.
	// For debugging usefulness it should be used to set the RAM to a host specific breakpoint instruction
	virtual void PoisonMemory() = 0;

protected:
	u8* region;
	size_t region_size;
	size_t parent_region_size;

	bool m_has_child;
	bool m_is_child;
	CodeBlock* m_child;

public:
	CodeBlock()
		: region(nullptr), region_size(0), parent_region_size(0),
		  m_has_child(false), m_is_child(false), m_child(nullptr)
	{
	}

	virtual ~CodeBlock() { if (region) FreeCodeSpace(); }

	// Call this before you generate any code.
	void AllocCodeSpace(int size, bool need_low = true)
	{
		region_size = size;
		region = (u8*)AllocateExecutableMemory(region_size, need_low);
		T::SetCodePtr(region);
	}

	// Always clear code space with breakpoints, so that if someone accidentally executes
	// uninitialized, it just breaks into the debugger.
	void ClearCodeSpace()
	{
		PoisonMemory();
		ResetCodePtr();
	}

	// Call this when shutting down. Don't rely on the destructor, even though it'll do the job.
	void FreeCodeSpace()
	{
		FreeMemoryPages(region, region_size);
		region = nullptr;
		region_size = 0;
		parent_region_size = 0;
		if (m_has_child)
		{
			m_child->region = nullptr;
			m_child->region_size = 0;
		}
	}

	bool IsInSpace(u8* ptr) const
	{
		return (ptr >= region) && (ptr < (region + region_size));
	}

	// Cannot currently be undone. Will write protect the entire code region.
	// Start over if you need to change the code (call FreeCodeSpace(), AllocCodeSpace()).
	void WriteProtect()
	{
		WriteProtectMemory(region, region_size, true);
	}

	void ResetCodePtr()
	{
		T::SetCodePtr(region);
	}

	size_t GetSpaceLeft() const
	{
		return (m_has_child ? parent_region_size : region_size) - (T::GetCodePtr() - region);
	}

	bool IsAlmostFull() const
	{
		// This should be bigger than the biggest block ever.
		return GetSpaceLeft() < 0x10000;
	}
	void AddChildCodeSpace(CodeBlock* child, size_t size)
	{
		_assert_msg_(DYNA_REC, !m_has_child, "Already have a child! Can't have another!");
		m_child = child;
		m_has_child = true;
		m_child->m_is_child = true;
		u8* child_region = region + region_size - size;
		m_child->region = child_region;
		m_child->region_size = size;
		m_child->ResetCodePtr();
		parent_region_size = region_size - size;
	}
};