/// <summary>
/// Redirects all calls from method 'from' to method 'to'. This version works
/// only if the 'from' method has already been compiled (use GetFunctionPointer to force
/// this) but no function calling 'from' have already been compiled. In fact, this
/// function forces compilation for 'to' and 'from'. 'to' and 'from' are assumed
/// to be normal methods.
/// After compilation, this method looks up the MonoJitInfo structs for both methods
/// from domain->jit_info_hash and patches sets the pointer to native code to the code
/// obtained from compiling 'to'.
/// </summary>
/// <param name="from"></param>
/// <param name="to"></param>
private static void RedirectCall(MethodInfo from, MethodInfo to)
{
/* We assume that we are only dealing with 'normal' functions (in Mono lingua).
* This excludes in particular:
* - generic functions
* - PInvokes
* - methods built at runtime
*/
IntPtr methodPtr1 = from.MethodHandle.Value;
IntPtr methodPtr2 = to.MethodHandle.Value;
// ensure that both methods are compiled
from.MethodHandle.GetFunctionPointer();
to.MethodHandle.GetFunctionPointer();
// get domain->jit_code_hash
IntPtr domain = mono_domain_get();
unsafe
{
byte * jitCodeHash = ((byte *)domain.ToPointer() + 0xE8);
long **jitCodeHashTable = *(long ***)(jitCodeHash + 0x20);
uint tableSize = *(uint *)(jitCodeHash + 0x18);
void *jitInfoFrom = null, jitInfoTo = null;
// imitate the behavior of mono_internal_hash_table_lookup to get both MonoJitInfo ptrs
long mptr1 = methodPtr1.ToInt64();
uint index1 = ((uint)mptr1) >> 3;
for (long *value = jitCodeHashTable[index1 % tableSize];
value != null;
value = *(long **)(value + 1))
{
if (mptr1 == *value)
{
jitInfoFrom = value;
break;
}
}
long mptr2 = methodPtr2.ToInt64();
uint index2 = ((uint)mptr2) >> 3;
for (long *value = jitCodeHashTable[index2 % tableSize];
value != null;
value = *(long **)(value + 1))
{
if (mptr2 == *value)
{
jitInfoTo = value;
break;
}
}
if (jitInfoFrom == null || jitInfoTo == null)
{
DebugLog.Log("Could not find methods");
return;
}
// copy over code_start, used_regs, code_size and ignore the rest for now.
// code_start beings at +0x10, code_size goes til +0x20
ulong *fromPtr, toPtr;
fromPtr = (ulong *)jitInfoFrom;
toPtr = (ulong *)jitInfoTo;
*(fromPtr + 2) = *(toPtr + 2);
*(fromPtr + 3) = *(toPtr + 3);
}
}