Nowadays x86_64 bzImage with a lot of built-in drivers may well be over 8 MB and
it will not boot with kernel_size limited at 8 MB. Increase the limit to 15 MB.

Reading file size at runtime could be a better solution.

diff -uNr elilo-3.16-source.orig/x86_64/bzimage.c elilo-3.16-source/x86_64/bzimage.c
--- elilo-3.16-source.orig/x86_64/bzimage.c	2012-11-19 22:01:04.000000000 +0100
+++ elilo-3.16-source/x86_64/bzimage.c	2014-05-14 13:44:00.352004159 +0200
@@ -34,7 +34,7 @@
 boot_params_t *param_start = NULL;
 UINTN param_size = 0;
 
-UINTN kernel_size = 0x800000;	/* 8M (default x86_64 bzImage size limit) */
+UINTN kernel_size = 0xF00000;
 
 static VOID *
 bzImage_alloc()