The confBEFORE macro is used to specify the presence of a special header file before compiling. The confBEFORE macro causes an appropriate BEFORE= directive to appear in your Makefile. It is very unlikely that you will ever have to change this from the value that is predefined for you. But if you do, you can do so like this illustration from SunOS 4.0:

define(`confBEFORE', `stdlib.h stddef.h limits.h')
PUSHDIVERT(3)
stddef.h stdlib.h limits.h:
        cp /dev/null $@
POPDIVERT

First, note that the declaration of confBEFORE requires a corresponding section of Makefile code to be inserted between diversions (PUSHDIVERT and POPDIVERT). The first line in this example says that the three files stdlib.h, stddef.h, and limits.h must exist in the obj... directory before sendmail can be compiled. It causes those three header files to be listed with the BEFORE= directive in the resulting Makefile:

BEFORE= stdlib.h stddef.h limits.h
...
sendmail: ${BEFORE} ${OBJS}

The diversion level 3 (in PUSHDIVERT) causes the two lines that follow to be inserted into the Makefile at the appropriate point. The diversion ends with POPDIVERT.

To illustrate further, suppose you want to include your own C-language source and header files with the Build of sendmail. One way to do this might be to add the following lines to your m4 build file:

APPENDDEF(`conf_sendmail_ENVDEF', `-DMYCODE')
APPENDDEF(`confBEFORE', `mycode.h')
APPENDDEF(`confSMOBJADD', `mycode.o')
PUSHDIVERT(3)
mycode.h mycode.c:
       ln -s /usr/local/src/mycode/$@
POPDIVERT

The first line adds -DMYCODE to the ENVDEF= line in Makefile (confENVDEF and conf_prog_ENVDEF). Here, we presume that C-language hooks have been added to the sendmail source, and that they are enabled/disabled by wrapping them in preprocessor conditionals.^[14] For example:

^[14] There is no method provided with the m4 technique to automatically patch hooks into sendmail. This is still a manual process.

# ifdef MYCODE
                if (mycode(e->e_eid) < 0)
                       return FALSE;
# endif

The second line in your m4 file appends mycode.h to this confBEFORE macro. The third line causes the OBJADD= directive in Makefile to be given the value mycode.o (confOBJADD). This automatically adds that object file name to the list of all object files in Makefile:

... util.o version.o ${OBJADD}

Finally, the diversion adds Makefile commands to ensure that the symbolic links to the required C-language source files exist before sendmail is compiled.