Manual browser: genassym(1)

GENASSYM(1) General Commands Manual GENASSYM(1)


genassymemit 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 “” in /usr/src/sys/kern. It became a userland utility in NetBSD 4.0.
April 13, 2010 NetBSD 7.0