CMake macro to detect glibc version by filename.

glibc.cmake

# - Check glibc version
# CHECK_GLIBC_VERSION()
# 
# Once done this will define
#
#   GLIBC_VERSION - glibc version
#
MACRO (CHECK_GLIBC_VERSION)
    EXECUTE_PROCESS (
        COMMAND ${CMAKE_C_COMPILER} -print-file-name=libc.so.6
	OUTPUT_VARIABLE GLIBC
	OUTPUT_STRIP_TRAILING_WHITESPACE)

    GET_FILENAME_COMPONENT (GLIBC ${GLIBC} REALPATH)
    GET_FILENAME_COMPONENT (GLIBC_VERSION ${GLIBC} NAME)
    STRING (REPLACE "libc-" "" GLIBC_VERSION ${GLIBC_VERSION})
    STRING (REPLACE ".so" "" GLIBC_VERSION ${GLIBC_VERSION})
    IF (NOT GLIBC_VERSION MATCHES "^[0-9.]+$")
        MESSAGE (FATAL_ERROR "Unknown glibc version: ${GLIBC_VERSION}")
    ENDIF (NOT GLIBC_VERSION MATCHES "^[0-9.]+$")
ENDMACRO (CHECK_GLIBC_VERSION)

Well, one thing which often works - not sure whether it always works - is run libc.so.6. Yes, it's typically executable - and prints version information.

It does not work for cross compiler, such as aarch64

Maybe you can implement CMake macro like

objdump -T `gcc -print-file-name=libc.so.6` \
  | grep -o 'GLIBC_[0-9]\+\(\.[0-9]\+\)*' \
  | sort -ruV \
  | head -1

Well, one thing which often works - not sure whether it always works - is run libc.so.6. Yes, it's typically executable - and prints version information.

It does not work for cross compiler, such as aarch64

Maybe you can implement CMake macro like

objdump -T `gcc -print-file-name=libc.so.6` \
  | grep -o 'GLIBC_[0-9]\+\(\.[0-9]\+\)*' \
  | sort -ruV \
  | head -1

realpath `gcc -print-file-name=libc.so.6`
/usr/lib/x86_64-linux-gnu/libc.so.6

Or adding one more line would be fine, like this.

MACRO (CHECK_GLIBC_VERSION)
    EXECUTE_PROCESS (
        COMMAND ${CMAKE_C_COMPILER} -print-file-name=libc.so.6
	OUTPUT_VARIABLE GLIBC
	OUTPUT_STRIP_TRAILING_WHITESPACE)

    GET_FILENAME_COMPONENT (GLIBC ${GLIBC} REALPATH)
    GET_FILENAME_COMPONENT (GLIBC_VERSION ${GLIBC} NAME)
    STRING (REPLACE "libc-" "" GLIBC_VERSION ${GLIBC_VERSION})
    STRING (REPLACE "libc" "" GLIBC_VERSION ${GLIBC_VERSION})  # added
    STRING (REPLACE ".so" "" GLIBC_VERSION ${GLIBC_VERSION})
    IF (NOT GLIBC_VERSION MATCHES "^[0-9.]+$")
        MESSAGE (FATAL_ERROR "Unknown glibc version: ${GLIBC_VERSION}")
    ENDIF (NOT GLIBC_VERSION MATCHES "^[0-9.]+$")
ENDMACRO (CHECK_GLIBC_VERSION)

Even added this line, it seems that only the major version of glibc can be extracted

MACRO (CHECK_GLIBC_VERSION)
	message("Checking GLIBC Version.")
	EXECUTE_PROCESS (
		COMMAND ${CMAKE_C_COMPILER} -print-file-name=libc.so.6
		OUTPUT_VARIABLE GLIBC
		OUTPUT_STRIP_TRAILING_WHITESPACE)

	GET_FILENAME_COMPONENT (GLIBC ${GLIBC} REALPATH)
	EXECUTE_PROCESS (
		COMMAND ${GLIBC}
		OUTPUT_VARIABLE GLIBC_OUTPUT
		ERROR_QUIET
		OUTPUT_STRIP_TRAILING_WHITESPACE)
	STRING (REGEX MATCH "release version ([0-9]+\\.[0-9]+)" GLIBC_VERSION ${GLIBC_OUTPUT})
	STRING (REPLACE "release version " "" GLIBC_VERSION ${GLIBC_VERSION})
	IF (NOT GLIBC_VERSION MATCHES "^[0-9.]+$")
		MESSAGE (FATAL_ERROR "Unknown glibc version: ${GLIBC_VERSION}")
	ENDIF (NOT GLIBC_VERSION MATCHES "^[0-9.]+$")
ENDMACRO (CHECK_GLIBC_VERSION)