pythonnet/src/runtime/platform/NativeCodePage.cs at master · sdpython/pythonnet · GitHub

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using System;

using System.Collections.Generic;

using System.Runtime.InteropServices;

namespace Python.Runtime.Platform

{

class NativeCodePageHelper

{

/// <summary>

/// Initialized by InitializeNativeCodePage.

///

/// This points to a page of memory allocated using mmap or VirtualAlloc

/// (depending on the system), and marked read and execute (not write).

/// Very much on purpose, the page is *not* released on a shutdown and

/// is instead leaked. See the TestDomainReload test case.

///

/// The contents of the page are two native functions: one that returns 0,

/// one that returns 1.

///

/// If python didn't keep its gc list through a Py_Finalize we could remove

/// this entire section.

/// </summary>

internal static IntPtr NativeCodePage = IntPtr.Zero;

/// <summary>

/// Structure to describe native code.

///

/// Use NativeCode.Active to get the native code for the current platform.

///

/// Generate the code by creating the following C code:

/// <code>

/// int Return0() { return 0; }

/// int Return1() { return 1; }

/// </code>

/// Then compiling on the target platform, e.g. with gcc or clang:

/// <code>cc -c -fomit-frame-pointer -O2 foo.c</code>

/// And then analyzing the resulting functions with a hex editor, e.g.:

/// <code>objdump -disassemble foo.o</code>

/// </summary>

internal class NativeCode

{

/// <summary>

/// The code, as a string of bytes.

/// </summary>

public byte[] Code { get; private set; }

/// <summary>

/// Where does the "return 0" function start?

/// </summary>

public int Return0 { get; private set; }

/// <summary>

/// Where does the "return 1" function start?

/// </summary>

public int Return1 { get; private set; }

public static NativeCode Active

{

get

{

switch (RuntimeInformation.ProcessArchitecture)

{

case Architecture.X86:

return I386;

case Architecture.X64:

return X86_64;

default:

return null;

}

/// <summary>

/// Code for x86_64. See the class comment for how it was generated.

/// </summary>

public static readonly NativeCode X86_64 = new NativeCode()

{

Return0 = 0x10,

Return1 = 0,

Code = new byte[]

{

// First Return1:

0xb8, 0x01, 0x00, 0x00, 0x00, // movl $1, %eax

0xc3, // ret

// Now some padding so that Return0 can be 16-byte-aligned.

// I put Return1 first so there's not as much padding to type in.

0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00, // nop

// Now Return0.

0x31, 0xc0, // xorl %eax, %eax

0xc3, // ret

}

};

/// <summary>

/// Code for X86.

///

/// It's bitwise identical to X86_64, so we just point to it.

/// <see cref="NativeCode.X86_64"/>

/// </summary>

public static readonly NativeCode I386 = X86_64;

}

/// <summary>

/// Platform-dependent mmap and mprotect.

/// </summary>

internal interface IMemoryMapper

{

/// <summary>

/// Map at least numBytes of memory. Mark the page read-write (but not exec).

/// </summary>

IntPtr MapWriteable(int numBytes);

/// <summary>

/// Sets the mapped memory to be read-exec (but not write).

/// </summary>

void SetReadExec(IntPtr mappedMemory, int numBytes);

}

class WindowsMemoryMapper : IMemoryMapper

{

const UInt32 MEM_COMMIT = 0x1000;

const UInt32 MEM_RESERVE = 0x2000;

const UInt32 PAGE_READWRITE = 0x04;

const UInt32 PAGE_EXECUTE_READ = 0x20;

[DllImport("kernel32.dll")]

static extern IntPtr VirtualAlloc(IntPtr lpAddress, IntPtr dwSize, UInt32 flAllocationType, UInt32 flProtect);

[DllImport("kernel32.dll")]

static extern bool VirtualProtect(IntPtr lpAddress, IntPtr dwSize, UInt32 flNewProtect, out UInt32 lpflOldProtect);

public IntPtr MapWriteable(int numBytes)

{

return VirtualAlloc(IntPtr.Zero, new IntPtr(numBytes),

MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);

}

public void SetReadExec(IntPtr mappedMemory, int numBytes)

{

UInt32 _;

VirtualProtect(mappedMemory, new IntPtr(numBytes), PAGE_EXECUTE_READ, out _);

}

class UnixMemoryMapper : IMemoryMapper

{

const int PROT_READ = 0x1;

const int PROT_WRITE = 0x2;

const int PROT_EXEC = 0x4;

const int MAP_PRIVATE = 0x2;

int MAP_ANONYMOUS

{

get

{

if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))

{

return 0x20;

}

else

{

// OSX, FreeBSD

return 0x1000;

}

[DllImport("libc")]

static extern IntPtr mmap(IntPtr addr, IntPtr len, int prot, int flags, int fd, IntPtr offset);

[DllImport("libc")]

static extern int mprotect(IntPtr addr, IntPtr len, int prot);

public IntPtr MapWriteable(int numBytes)

{

// MAP_PRIVATE must be set on linux, even though MAP_ANON implies it.

// It doesn't hurt on darwin, so just do it.

return mmap(IntPtr.Zero, new IntPtr(numBytes), PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, IntPtr.Zero);

}

public void SetReadExec(IntPtr mappedMemory, int numBytes)

{

mprotect(mappedMemory, new IntPtr(numBytes), PROT_READ | PROT_EXEC);

}

internal static IMemoryMapper CreateMemoryMapper()

{

if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))

{

return new WindowsMemoryMapper();

}

else

{

// Linux, OSX, FreeBSD

return new UnixMemoryMapper();

}

/// <summary>

/// Initializes the native code page.

///

/// Safe to call if we already initialized (this function is idempotent).

/// <see cref="NativeCodePage"/>

/// </summary>

internal static void InitializeNativeCodePage()

{

// Do nothing if we already initialized.

if (NativeCodePage != IntPtr.Zero)

{

return;

}

// Allocate the page, write the native code into it, then set it

// to be executable.

IMemoryMapper mapper = CreateMemoryMapper();

int codeLength = NativeCode.Active.Code.Length;

NativeCodePage = mapper.MapWriteable(codeLength);

Marshal.Copy(NativeCode.Active.Code, 0, NativeCodePage, codeLength);

mapper.SetReadExec(NativeCodePage, codeLength);

}

pythonnet/src/runtime/platform/NativeCodePage.cs at master · sdpython/pythonnet · GitHub

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