Date: Fri, 9 Dec 2011 07:51:27 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-drivers@freebsd.org Cc: some body <bsd.mharv@gmail.com> Subject: Re: boot0.S empty #ifdef Message-ID: <201112090751.27804.jhb@freebsd.org> In-Reply-To: <CAJy8JvR0XNDYAY0530CyhFK4LQNVSiJqfuM=-oGWZmBaLe0rdw@mail.gmail.com> References: <CAJy8JvR0XNDYAY0530CyhFK4LQNVSiJqfuM=-oGWZmBaLe0rdw@mail.gmail.com>
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On Monday, December 05, 2011 2:30:30 pm some body wrote: > I am starting to learn how the kernel works and have started by going > through the boot loader and I've noticed that between lines 21-32 in > boot0.S there are some empty #ifdef statements. I was wondering a) where > are these paramaters defined and if they are defined, what difference does > it make since it looks like it doesn't change anything since they're empty? > > > #ifdef SIO > #endif > > #ifdef CHECK_DRIVE > #endif > > #ifdef ONLY_F_KEYS > #endif It seems the point of these is to document what they do (note that you left out the comments): /* build options: */ #ifdef SIO /* use serial console on COM1. */ #endif #ifdef PXE /* enable PXE/INT18 booting with F6 */ #define SAVE_MORE_MEMORY #endif #ifdef CHECK_DRIVE /* make sure we boot from a HD. */ #endif #ifdef ONLY_F_KEYS /* Only F1..F6, no digits on console */ #endif #ifdef VOLUME_SERIAL /* support Volume serial number */ #define B0_BASE 0x1ae /* move the internal data area */ #define SAVE_MEMORY #else #define B0_BASE 0x1b2 #endif #ifdef TEST /* enable some test code */ #define SAVE_MEMORY #define SAVE_MORE_MEMORY #endif -- John Baldwin
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