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thunk.cpp
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143 lines (118 loc) · 3.34 KB
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#include "core.h"
#include "thunk.h"
#if defined(_WINDOWS)
#include <windows.h>
#include <cstdlib>
// This holds the handle to a private heap that will allocate executable memory.
// We can't use normal memory for this as 'Data Execution Prevention' would
// cause faults when we try and run our dynamically built code.
//
static HANDLE s_thunk_heap = nil;
struct Trampoline
{
#pragma pack(push, 1)
unsigned short lea_ecx;
unsigned long this_ptr;
unsigned char mov_eax;
unsigned long jump_ptr;
unsigned short jmp_eax;
#pragma pack(pop)
};
struct TrampolineStdCall
{
#pragma pack(push, 1)
unsigned char pop_eax;
unsigned char push_ptr;
unsigned long this_ptr;
unsigned char push_eax;
unsigned char mov_eax;
unsigned long jump_ptr;
unsigned short jmp_eax;
#pragma pack(pop)
};
bool MCThunkInitialize(void)
{
s_thunk_heap = HeapCreate(HEAP_CREATE_ENABLE_EXECUTE, 0, 0);
if (s_thunk_heap == nil)
return false;
return true;
}
void MCThunkFinalize(void)
{
if (s_thunk_heap != nil)
{
HeapDestroy(s_thunk_heap);
s_thunk_heap = nil;
}
}
bool MCThunkNew(void *p_object, void *p_method, void*& r_closure)
{
// If the heap isn't initialized yet, then initialize it.
if (s_thunk_heap == nil)
return false;
// Allocate the trampoline structure in our exectuable heap.
Trampoline *t_trampoline;
t_trampoline = static_cast<Trampoline *>(HeapAlloc(s_thunk_heap, 0, sizeof(Trampoline)));
if (t_trampoline == nil)
return false;
// Set up the trampoline code. This sequence of bytes is the following asm:
// lea ecx, ds:[p_object]
// mov eax, p_method
// jmp eax
//
t_trampoline -> lea_ecx = 0x0D8D;
t_trampoline -> this_ptr = (long)p_object;
t_trampoline -> mov_eax = 0xB8;
t_trampoline -> jump_ptr = (long)p_method;
t_trampoline -> jmp_eax = 0xE0FF;
// On some architectures, explicit flushing needs to be performed on the
// instruction cache to make sure stale code is not executed.
FlushInstructionCache(GetCurrentProcess(), t_trampoline, sizeof(Trampoline));
r_closure = t_trampoline;
return true;
}
bool MCThunkNewStdCall(void *p_object, void *p_method, void*& r_closure)
{
// If the heap isn't initialized yet, then initialize it.
if (s_thunk_heap == nil)
return false;
// Allocate the trampoline structure in our exectuable heap.
TrampolineStdCall *t_trampoline;
t_trampoline = static_cast<TrampolineStdCall *>(HeapAlloc(s_thunk_heap, 0, sizeof(TrampolineStdCall)));
if (t_trampoline == nil)
return false;
// Set up the trampoline code. This sequence of bytes is the following asm:
// pop eax
// push <p_object>
// push eax
// mov eax, <method>
// jmp eax
//
t_trampoline -> pop_eax = 0x58;
t_trampoline -> push_ptr = 0x68;
t_trampoline -> this_ptr = (long)p_object;
t_trampoline -> push_eax = 0x50;
t_trampoline -> mov_eax = 0xB8;
t_trampoline -> jump_ptr = (long)p_method;
t_trampoline -> jmp_eax = 0xE0FF;
// On some architectures, explicit flushing needs to be performed on the
// instruction cache to make sure stale code is not executed.
FlushInstructionCache(GetCurrentProcess(), t_trampoline, sizeof(Trampoline));
r_closure = t_trampoline;
return true;
}
void MCThunkDelete(void *p_closure)
{
if (p_closure == nil)
return;
HeapFree(s_thunk_heap, 0, p_closure);
}
#else
bool MCThunkNew(void *p_object, void *p_method, void*& r_closure)
{
return false;
}
void MCThunKDelete(void *p_closure)
{
}
#endif