I ran into another one I did not notice earlier.
As a side note i've patched my local copy of backend/ptrntab.c to include two opcodes SYSCALL/SYSRET but I don't know how to properly handle SYSRET for 64bit mode as it needs a REX.w prefix
===
/*
Disassembly of section .text._D1a1aFZv:
0000000000000000 <_D1a1aFZv>:
0: 48 89 c2 mov %rax,%rdx
3: 48 89 c2 mov %rax,%rdx
*/
void a() { asm {
naked;
mov RDX, RAX;
mov R10, RAX; // should have REX.b set ( 49 89 c2 )
} }