linux-kernel - RE: [PATCH 0/5] cramfs refresh for embedded usage

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Date:   Mon, 14 Aug 2017 13:31:47 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Chris Brandt <Chris.Brandt@...esas.com>
cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-embedded@...r.kernel.org" <linux-embedded@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 0/5] cramfs refresh for embedded usage

On Mon, 14 Aug 2017, Chris Brandt wrote:

> On Friday, August 11, 2017, Nicolas Pitre wrote:
> > This series brings a nice refresh to the cramfs filesystem, adding the
> > following capabilities:
> > 
> > - Direct memory access, bypassing the block and/or MTD layers entirely.
> > 
> > - Ability to store individual data blocks uncompressed.
> > 
> > - Ability to locate individual data blocks anywhere in the filesystem.
> > 
> > The end result is a very tight filesystem that can be accessed directly
> > from ROM without any other subsystem underneath. Also this allows for
> > user space XIP which is a very important feature for tiny embedded
> > systems.
> 
> 
> 
> I just applied the patches tried this simple test:
>  - tested with a Renesas RZ/A1 (Cortex-A9...so it has an MMU).
>  - I set the sticky bit for busybox before using mkcramfs

You need the newer mkcramfs I linked to in the documentation. With it 
you don't need to play tricks with the sticky bit anymore. However you 
need to specify -X twice (or just once for no-MMU targets) and it will 
make every ELF files XIPable automatically.

>  - booted (with squashfs) and mounted the cramfs image
>  - confirmed that the sticky bit was still set on busybox
>  - was able to execute busybox in the cramfs image
> 
> 
> However, at this point I'm not sure how I can confirm that the XIP 
> busybox actually executed as XIP or not.

Just use busybox's built-in cat command and dump the content of 
/proc/self/maps. You should see an offset that refers to a physical 
address within your cramfs image for those segments marked read-only and 
executable.


Nicolas