genassym —
emit an assym.h file
  
    | genassym | [ -c] [-f]
      C compiler invocation | 
genassym is a shell script normally used during the
  kernel build process to create an assym.h file. This file defines a number of
  cpp constants derived from the configuration information
  genassym reads from stdin. The generated file is used
  by kernel sources written in assembler to gain access to information (e.g.
  structure offsets and sizes) normally only known to the C compiler.
Arguments to genassym are usually of the
    form ${CC} ${CFLAGS} ${CPPFLAGS} where
    ${CC} is the C compiler used to compile the kernel,
    while ${CFLAGS} and ${CPPFLAGS}
    are flag arguments to the C compiler. The script creates a C source file
    from its input. Then the C compiler is called according to the script's
    arguments to compile this file.
Normally genassym instructs the C compiler
    to create an assembler source from the constructed C source. The resulting
    file is then processed to extract the information needed to create the
    assym.h file. The -c flag instructs
    genassym to create slightly different code, generate
    an executable from this code and run it. In both cases the assym.h file is
    written to stdout. The -f flag instructs
    genassym to create forth code.
Either self-explanatory, or generated by one of the programs called from the
  script.
The genassym command appeared in NetBSD
  1.3 as “genassym.sh” in
  /usr/src/sys/kern. It became a userland utility in
  NetBSD 4.0.