Date: Mon, 21 Jan 2008 01:38:48 +0100 From: Bernd Walter <ticso@cicely12.cicely.de> To: Adrian Penisoara <ady@freebsd.ady.ro> Cc: freebsd-hackers@freebsd.org Subject: Re: Squeezing out some 70 bytes out of the boot2 loader Message-ID: <20080121003847.GI22192@cicely12.cicely.de> In-Reply-To: <78cb3d3f0801201239x18c339a6sbc6a04d2b5670b81@mail.gmail.com> References: <78cb3d3f0801201239x18c339a6sbc6a04d2b5670b81@mail.gmail.com>
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On Sun, Jan 20, 2008 at 10:39:45PM +0200, Adrian Penisoara wrote: > Hello > > I am trying to hack in some symlink support into the [sys/boot/i386/]boot2 > bootloader (for my project [1]) and I seem to fall short of about 69 bytes: > > as -o boot2.o boot2.s > ld -static -N --gc-sections -nostdlib -Ttext 0x2000 -o > boot2.out/build/obj/build/src/sys/boot/i386/boot2/../btx/lib/crt0.o > boot2.o sio.o > objcopy -S -O binary boot2.out boot2.bin > btxld -v -E 0x2000 -f bin -b > /build/obj/build/src/sys/boot/i386/boot2/../btx/btx/btx -l boot2.ldr -o > boot2.ld -P 1 boot2.bin > kernel: ver=1.01 size=7b0 load=9000 entry=9010 map=16M pgctl=1:1 > client: fmt=bin size=1581 text=0 data=0 bss=0 entry=0 > output: fmt=bin size=1e45 text=114 data=1d31 org=0 entry=0 > -69 bytes available > *** Error code 1 > > What can I do to get room for about 70-100 bytes for these changes to make > it into the bootloader ? > > [1] I'm trying to get support for /boot being mounted as a separate FS and > as such I would need to have a "self-pointing" symlink (e.g. "boot -> ." ) > to easily mask the fact that the boot stuff is now right in the root of that > FS. Fortunately the FORTH loader does support symlinks and I do not get > problems with it. I know that I can use /boot.kernel as a workaround, but > that is not too elegant. The support is already there - at least to some definition. You just need to symlink it the other way, so the kernel sees the symlink and not the bootcode: Mount your boot-FS into /bootdir with a /boot subdir inside. So on ypur running system you have /bootdir/boot. Then symlink /boot on your real /-FS to /bootdir/boot and you are fine with tools expecting /boot on your running system. Fill the directory with the usual content. boot2 and later loader stages will just see it's normal /boot inside with everything in it. This is already published on http://wiki.freebsd.org/ZFSOnRoot for having a non UFS filesystem as /. -- B.Walter http://www.bwct.de http://www.fizon.de bernd@bwct.de info@bwct.de support@fizon.de
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