---
name: "genassym.cf"
section: "5"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/genassym.cf"
---

# genassym.cf(5)

assym.h definition file

## NAME

**genassym.cf** – assym.h definition file

## DESCRIPTION

The **genassym.cf** file is used by [genassym.sh(8)](/genassym.sh/8.md) to make constant C expressions known to assembler source files.

Lines starting with '#' are discarded by [genassym.sh(8)](/genassym.sh/8.md). Lines starting with *include*, *ifdef*, *if*, *else* or *endif* are preceded with '#' and passed otherwise unmodified to the C compiler.

Lines starting with *quote* get passed on with the *quote* command removed.

The first word after a *define* command is taken as a CPP identifier and the rest of the line has to be a constant C expression. The output of [genassym.sh(8)](/genassym.sh/8.md) will assign the numerical value of this expression to the CPP identifier.

*export foo*\
 is a shorthand for\
 *define foo foo*.

*struct foo*\
 remembers foo for the *member* command and does a\
 *define FOO\_SIZEOF sizeof(foo)*,\
 with the structure name converted to upper case.

*member foo*\
 does a\
 *define FOO offsetof(\<last struct\>, foo)*.\
 The two argument form of *member*, as\
 *member foo bar*\
 does a\
 *define FOO offsetof(\<last struct\>, bar)*,\
 with its first argument converted to upper case. In the case where struct was invoked with an extra argument, as in\
 *struct foo PREFIX\_*,\
 the first argument of member will be prefixed by the remembered prefix, before being converted to upper case.

*union foo*\
 is similar to the *struct* command, but applies to a union instead of a struct.

*config \<ctype\> \<gcc constraint\> \<asm print modifier\>*\
 can be used to customize the output of [genassym.sh(8)](/genassym.sh/8.md).\
 When producing C output, values are cast to \<ctype\> (default: long) before they get handed to printf. \<gcc constraint\> (default: n) is the constraint used in the \_\_asm\_\_ statements. \<asm print modifier\> (default: empty) can be used to force gcc to output operands in different ways than normal. The "a" modifier e.g. stops gcc from emitting immediate prefixes in front of constants for the i386 port.

## FILES

*/sys/arch/${MACHINE}/${MACHINE}/genassym.cf*

## SEE ALSO

[genassym.sh(8)](/genassym.sh/8.md)

## HISTORY

The first use of **genassym.cf** files occurred in OpenBSD 2.2. Its use was generalized to all ports for OpenBSD 3.0. The *union* command appeared in OpenBSD 3.5.