linux-kernel - Re: [PATCH 9/33] i386 boot: Add serial output support to the decompressor

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Date:	Wed, 2 Aug 2006 07:21:44 +0200
From:	Andi Kleen <ak@...e.de>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	linux-kernel@...r.kernel.org, Horms <horms@...ge.net.au>,
	Jan Kratochvil <lace@...kratochvil.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Magnus Damm <magnus.damm@...il.com>,
	Vivek Goyal <vgoyal@...ibm.com>, Linda Wang <lwang@...hat.com>
Subject: Re: [PATCH 9/33] i386 boot: Add serial output support to the decompressor

On Wednesday 02 August 2006 06:57, Eric W. Biederman wrote:
> Andi Kleen <ak@...e.de> writes:
> 
> >> > Actually the best way to reuse would be to first do 64bit uncompressor
> >> > and linker directly, but short of that #includes would be fine too.
> >> 
> >> > Would be better to just pull in lib/string.c
> >> 
> >> Maybe.  Size is fairly important 
> >
> > Why is size important here?
> 
> For the same reason that we compress the kernel. ;)
> 
> This is the one chunk of code that we don't compress so every extra
> byte makes our executable bigger.  Now I think the code size is
> actually in the 32k - 64k range so as long as it is a minor change
> it doesn't really matter.

   text    data     bss     dec     hex filename
   1909     352      12    2273     8e1 arch/x86_64/kernel/early_printk.o
   2212       0       0    2212     8a4 lib/string.o

It's minor.

> 
> The big pain with using lib/string.c and
> arch/x86_64/kernel/early_printk.c is that it is significant change
> in how the code of misc.c is constructed.  

Not if you use #include

> Which means some 
> serious reevaluation of all kinds of things need to be considered.
> Making it a lot of work :)
> 
> One of the practical dangers is that we make it more likely
> we can kill the boot by messing up the shared code.

If they're messed up the later boot will fail too. Doesn't make
too much difference.

> 
> I'm not certain what to think when even including normal
> kernel headers causes problems.  It certainly makes me leery
> of including normal kernel code.  But it might simplify some
> of the problems too.

On x86-64 some trouble comes from it being 32bit code. 
That is why I suggested making it 64bit first, which would
avoid many of the problems.
 
> Whichever way I go scrutinizing that possibility carefully is
> a lot of work.

64bit conversion would be some work, the rest isn't I think.

Alternatively if you don't like it we can just drop these compressor patches.
I don't think they were essential.

-Andi
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