The asembler files were not built with no-exec.
from notes from jakub:
assembly is by default conservatively assumed to need executable stack
you need either:
1) .section .note.GNU-stack,"",@progbits somewhere in the assembly
2) assemble with -Wa,--noexecstack or 3) link with -Wl,-z,noexecstack
3) if it is already linked, you can use the execstack(8) utility