[winasan] Reduce hotpatch prefix check to 8 bytes

[dmajor]

Summary

Same idea as r310419: The 8 byte nop is a suffix of the 9 byte nop, and we need at most 6 bytes.

[dmajor]

This isn't strictly necessary for anything; I was just debugging something and noticed that a hook fell back to Trampoline rather than Hotpatch because the prefix nop was only 8 bytes.

[rnk]

lgtm

I see that we've done this before in rL310419. This was originally added in rL275180. It'd be nice to figure out what tools generate this nop so we can enumerate all the patterns, but for now let's just do this.

lib/interception/interception_win.cc

 static bool IsMemoryPadding(uptr address, uptr size) {
   u8* function = (u8*)address;
   for (size_t i = 0; i < size; ++i)
     if (function[i] != 0x90 && function[i] != 0xCC)
       return false;
   return true;
 }
 
-static const u8 kHintNop9Bytes[] = {
-  0x66, 0x0F, 0x1F, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00
+static const u8 kHintNop8Bytes[] = {
+  0x0F, 0x1F, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00
 };
 
 template<class T>
 static bool FunctionHasPrefix(uptr address, const T &pattern) {
   u8* function = (u8*)address - sizeof(pattern);
   for (size_t i = 0; i < sizeof(pattern); ++i)
     if (function[i] != pattern[i])
       return false;
   return true;
 }
 
 static bool FunctionHasPadding(uptr address, uptr size) {
   if (IsMemoryPadding(address - size, size))
     return true;
-  if (size <= sizeof(kHintNop9Bytes) &&
-      FunctionHasPrefix(address, kHintNop9Bytes))
+  if (size <= sizeof(kHintNop8Bytes) &&
+      FunctionHasPrefix(address, kHintNop8Bytes))
     return true;
   return false;
 }
 
 static void WritePadding(uptr from, uptr size) {
   _memset((void*)from, 0xCC, (size_t)size);
 }