FreeBSD Porter's Handbook
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# 12.11 Respect `CFLAGS`

The port should respect the `CFLAGS` variable. What we mean by this is that the port should not set the value of this variable absolutely, overriding the existing value; instead, it should append whatever values it needs to the existing value. This is so that build options that affect all ports can be set globally.

If it does not, please add `NO_PACKAGE=ignores cflags` to the `Makefile`.

An example of a `Makefile` respecting the `CFLAGS` variable follows. Note the `+=`:

    CFLAGS+= -Wall -Werror

Here is an example which does not respect the `CFLAGS` variable:

    CFLAGS= -Wall -Werror

The `CFLAGS` variable is defined on FreeBSD systems in `/etc/make.conf`. The first example appends additional flags to the `CFLAGS` variable, preserving any system-wide definitions. The second example clobbers anything previously defined.

You should remove optimization flags from the third party `Makefile`s. System `CFLAGS` contains system-wide optimization flags. An example from an unmodified `Makefile`:

    CFLAGS= -O3 -funroll-loops -DHAVE_SOUND

Using system optimization flags, the `Makefile` would look similar to the following example:

    CFLAGS+= -DHAVE_SOUND

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