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https://cmake.org/cmake/help/v3.14/variable/CMAKE_LANG_ARCHIVE_CREATE.html doesn't treat ASM differently from C and C++ and doesn't say CMAKE_ASM_ARCHIVE_CREATE is missing. However defining CMAKE_ASM_ARCHIVE_CREATE and friends is silently ignored.

Comparing [/usr/share/cmake/Modules/] CMakeASMInformation.cmake with CMakeCInformation.cmake and CMakeCXXInformation.cmake in version 3.14, one can see that CMAKE_ASM_ARCHIVE_CREATE and friends simply don't exist.

Maybe _ASM is different by design and this Works As Intended? In such a case please consider as a missing documentation bug.

Workarounds:

• Add at least one (empty) C file to add_library(): add_library(a.s b.S ... empty.c) and use CMAKE_C_ARCHIVE_CREATE instead. See tested example at https://github.com/zephyrproject-rtos/zephyr/pull/17632/
• Provide the entire, higher level CMAKE_ASM_CREATE_STATIC_LIBRARY function instead. This runs into other issues, see #19474

Test code for quick reproduction:

# Test with:
#
#   rm -rf build/; cmake -B build && make -C build VERBOSE=1 mylib

cmake_minimum_required(VERSION 3.14)
project(assembly_lib ASM C)

add_library(mylib STATIC hello_main.S)

# Documented at
# https://cmake.org/cmake/help/v3.14/variable/CMAKE_LANG_ARCHIVE_CREATE.html
# but not implemented in Modules/CMakeASMInformation.cmake and silently ignored.
SET(CMAKE_ASM_ARCHIVE_CREATE
      "<CMAKE_AR> qc -should_fail_but_ignored <TARGET> <LINK_FLAGS> <OBJECTS>")


# Optional, just in case you want to actually run the code.
# add_executable(myexe something.c) # something.c can be empty too
# target_link_libraries(myexe mylib)