[H-GEN] Reducing kernel memory footprint?

[Chris Baird]

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Martin,
> It may be possible to configure gcc to run its various stages (cpp, cc1,
> cc2, as, ld) in sequence: I think by default it tries to run them at the
> same time with pipes connecting them.

That's "-pipe".  It's in Linux makefiles as a default now, as anyone
who've compiled with recent compiler tools on a 8M machine will
testify.

> Another interesting thing would be to call the stages directly, rather
> than through the gcc driver: run gcc -V (or should that be -v?) and put
> that into your script.  Of course you should be running from a shell
> script or direct from emacs, not from Make.

With memory this small it actually doesn't add much bypassing make--
loading in anything will see other programs paged out completely to
vm, as if they weren't there to begin with.

> Also, when compiling the kernel and large binaries you should look at
> the -f alignment options, which let you get a crude space-speed tradeoff
> on platforms like x86 that can do unaligned access.

I've gone through all them, including the undocumented ones. :) For a
i386, the best combination so far has been "-O2 -malign-loops=0
-malign-jumps=0 -malign-functions=0".  I've even recompiled gcc
(2.5.8->2.95.2, couldn't get 1.40 to work) trying to get a smaller
cc1, but the differences between the versions was negligible...

Anyway, I spent most of today going through kernel source and ripping
out all the crap (APM/PCI/Pentium/SMP/noni386/...)  Currently the
footprint's at 880kB, and the source fits onto a single _720kB_
floppy. :)

-- 
Chris,,
[1] as someone coming from a NetBSD cradle, seeing code like:
	#ifdef CONFIG_PCI
	mumble
	#endif
	#ifdef CONFIG_APM
	mumble
	#include <mumble.h>
	for (tmp = 0; tmp < set_proc_mumble(); tmp += mumble) {
	#endif
	mumble
	#ifdef mumble
	    }
	}
	#endif
	#else
	#include <mumblefoo.h>
...deep inside Torvalds' sacred code, made me wish that cpp abuse was
a felony. :P

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