// We'll need the index registers, which belong to the caller in this
// ABI.
push rsi
+ .seh_pushreg rsi
push rdi
+ .seh_pushreg rdi
+ .seh_endprologue
// Move arguments to more useful places.
mov SI, r8 // key material
# define SRC rdx
# define DST r8
# define NR eax
+ .seh_endprologue
#endif
// Find the magic endianness-swapping table.