[PATCH v2 0/5] make XIP kernel .data compressed in ROM

[Nicolas Pitre]

On Wed, 30 Aug 2017, Chris Brandt wrote:

> On Tuesday, August 29, 2017 1, Nicolas Pitre wrote:
> > This patch series provides the ability to store the XIP kernel .data
> > segment compressed in ROM. It has to be copied to RAM anyway so
> > storing it uncompressed is arguably a waste of ROM resources.
> > 
> > While at it, the copying of .data (when not compressed) and the
> > clearing of .bss is now performed using optimized string routines
> > rather than doing it one word at a time.
> 
> Tested on my XIP system (Cortex-A9) and it seems to work OK.

Good, thanks for testing.

> > This work highlighted some defficiencies in linker scripts, especially
> > the XIP one. So this also includes linker script cleanups and fixes.
> 
> Thank you for this!

More will come eventually.

Did this fix your cramfs issue with 4.13-rc7?

> If you're curious, here are some numbers from my system:
> 
> Original xipImage size: 4,190,068 bytes
> xipImage size with CONFIG_XIP_DEFLATED_DATA=y: 3,985,227 bytes
> 
> A 204,841 byte reduction in image size (4.89%)

In my case it is 1195492 vs 1111632, or a 7% reduction.

This could be improved further by locating most of init.data and 
init.text into the compressed zone even if it is read-only. The 
decompressed form would be located in RAM temporarily and discarded 
after boot. Right now it is left uncompressed in ROM forever. But that's 
for a later round.


Nicolas