Date: Thu, 31 Jan 2008 19:58:35 +0100 From: Eduardo Morras <nec556@retena.com> 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: <4760B89802390B84@> (added by postmaster@resmaa07.ono.com) In-Reply-To: <78cb3d3f0801201239x18c339a6sbc6a04d2b5670b81@mail.gmail.co m> References: <78cb3d3f0801201239x18c339a6sbc6a04d2b5670b81@mail.gmail.com>
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At 21:39 20/01/2008, you 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.
How big is boot2? You can compress it with an arithmetic coder, and
only put the decoder plus the compressed boot2. There are very tiny
arith coders, in assm, with 100-120 bytes of code (even less).
----------------------------------------------------------------------------------------------------------------
One reason that life is complex is that it has a real part and an
imaginary part
-Andrew Koenig
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