JumpPatchSites can/should easily deal with uint8 sized offsets.

src/x64/ic-x64.cc

Index: src/x64/ic-x64.cc
diff --git a/src/x64/ic-x64.cc b/src/x64/ic-x64.cc
index b998e0db82e3a406a2bfdf2a752e0d0eb3ff34d8..cf2346272b8d92fcad834605b1a378e6759f9b8d 100644
--- a/src/x64/ic-x64.cc
+++ b/src/x64/ic-x64.cc
@@ -1303,7 +1303,7 @@ void PatchInlinedSmiCode(Address address, InlinedSmiCheck check) {
   Address delta_address = test_instruction_address + 1;
   // The delta to the start of the map check instruction and the
   // condition code uses at the patched jump.
-  int8_t delta = *reinterpret_cast<int8_t*>(delta_address);
+  uint8_t delta = *reinterpret_cast<uint8_t*>(delta_address);
   if (FLAG_trace_ic) {
     PrintF("[  patching ic at %p, test=%p, delta=%d\n",
            address, test_instruction_address, delta);