Le 06/10/2022 à 22:45, Segher Boessenkool a écrit :

On Thu, Oct 06, 2022 at 06:38:00PM +0000, Christophe Leroy wrote:

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Le 06/10/2022 à 20:22, Segher Boessenkool a écrit :

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Long ago I built kernels that fit together with the boot firmware and a
root fs (busybox+dropbear essentially) in 4MB, but I doubt we can get
close to that at all these days :-)

4MB, not easy. But 8M still achievable. Well our smaller board has 32M,
we have thousands of it spread all over Europe and have to keep it up to
date ....

The smallest of these systems had 256MB RAM.  This 4MB is flash ROM :-)

I fit Uboot + DTB + Kernel + Initramfs with klibc and mtdutils in a 2MB 
flash ROM.

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What is the overhead if you enable modules but do not use them, these
days?

On the 8xx it is mainly the instruction TLB miss handler:

I meant just an indicative code size number...  100 bytes, 100kB, 100MB,
or something like that :-)  And, on 64 bit, which is what the question
was about!

Ah, does the size really matters here ? I was thinking more in terms of 
performance when I made the comment.

Christophe