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Building an Alternate Kernel Configuration

When building a kernel, you may want to build a configuration other than the RELEASE configuration (the default shipping configuration). Additional configurations are RELEASE_TRACE, DEBUG, DEBUG_TRACE, and PROFILE. These configurations add various additional options (except PROFILE, which is reserved for future expansion, and currently maps onto RELEASE).

The most useful and interesting configurations are RELEASE and DEBUG. The release configuration should be the same as a stock Apple-released kernel, so this is interesting only if you are building source that differs from that which was used to build the kernel you are already running. Compiling a kernel without specifying a configuration results in the RELEASE configuration being built.

The DEBUG configuration enables ddb, the in-kernel serial debugger. The ddb debugger is helpful to debug panics that occur early in boot or within certain parts of the Ethernet driver. It is also useful for debugging low-level interrupt handler routines that cannot be debugged by using the more traditional gdb.

To compile an alternate kernel configuration, you should follow the same basic procedure as outlined previously, changing the final make statement slightly. For example, to build the DEBUG configuration, instead of typing

make all

you type

make KERNEL_CONFIGS=DEBUG all

and wait.

To turn on additional compile options, you must modify one of the MASTER files. For information on modifying these files, see the section “Enabling Module Options”.

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