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

On Wed, 30 Aug 2017, Chris Brandt wrote:

On Tuesday, August 29, 2017 1, Nicolas Pitre wrote:

quoted

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.

quoted

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