[fasm2] macro for making ELF64 x86-64 Linux executables

I wrote a set of macros for producing ELF64 x86-64 Linux executable binaries.
https://github.com/cbytensky/fasm2-elf64
Examples. HelloWorld using syscalls:

Code:

include "elf64.inc"
        sys         write, 1, <"hello, world", 10>, @$
        sys         exit, 0

Produces 148-byte ELF64.
HelloWorld using libc:

Code:

include "elf64.inc"
needed "libc.so.6"
        dyncallz    puts, "hello, world"
        dyncall     _exit, 0

Produces 464-byte ELF64.

Implemented:

Dynamic linking (PT_INTERP/PT_DYNAMIC segments), no external linker required. Enabled automatically if "needed" and "dyncall" used.
Automatic symbols importing (like "puts" or "_exit" from "libc.so.6" in example).
Named Linux syscalls ("write", "exit").
SysV ABI call macros "sys", "dyncall", "dyncallz" (which is like "dyncall" but appends zero byte to all string arguments).
"@" contains the address of the last string argument.
"@$" contains the size in bytes of the last string argument (in example it is 13, the length of <"hello, world", 10>).
"movopt" macro for size/speed-optimized data transfer using mov/xor/push-pop.
"@optspeed" and "@optsize" macros that switches optimization strategy of "movopt" macro.
1 file, 335 lines.

Non-features/limitations:

Poor tool compatibility (like readelf/objdump/gdb). Optimized for minimal size.
No section header table.
No FP support for SysV ABI calls.