opcode for endbr64 (yasm doesn't handle it directly) 

Index: third_party/x86inc/x86inc.asm
--- third_party/x86inc/x86inc.asm.orig
+++ third_party/x86inc/x86inc.asm
@@ -860,6 +860,9 @@ BRANCH_INSTR jz, je, jnz, jne, jl, jle, jnl, jnle, jg,
     %endif
     align function_align
     %2:
+    %if VPX_ARCH_X86_64
+        dd 0xfa1e0ff3
+    %endif
     RESET_MM_PERMUTATION        ; needed for x86-64, also makes disassembly somewhat nicer
     %xdefine rstk rsp           ; copy of the original stack pointer, used when greater alignment than the known stack alignment is required
     %assign stack_offset 0      ; stack pointer offset relative to the return address