Re: [Xen-devel] [RFC 6/6] xen/arm: Replace early_printk call to printk call

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-02-20 at 11:14 +0000, Julien Grall wrote:
> 
> On 20/02/14 11:05, Ian Campbell wrote:
> > On Thu, 2014-02-20 at 11:01 +0000, Julien Grall wrote:
> >>
> >> On 20/02/14 09:04, Ian Campbell wrote:
> >>> I was actually thinking more along the lines of a .word at a defined
> >>> offset which you could hex edit to a specific value to activate a
> >>> particular flavour of early printk handling. That would be sufficient
> >>> e.g. for osstest to activate the appropriate stuff for the specific
> >>> platform.
> >>
> >> I don't see useful use case to have a such early printk implementation
> >> in Xen. When the board is fully supported, failed at early stage (e.g
> >> before console is initialized) is very unlikely. At least if you don't
> >> play with memory.
> >
> > a) there are boards which aren't fully supported, getting some debug out
> > of a distro package might be useful
> 
> Few months ago we have decided to allow early printk only when Xen is 
> compiled with debug enabled. It seems a big mistake to ship distro with 
> debug enabled :).

This was because earlyprintk only supports a static single configuration
at compile time. If that restriction was lifted then there would be no
reason to limit earlyprintk to debug builds.

> > b) even for boards which are fully supported there may still be bugs
> > which only appear under particular circumstances.
> 
> I understand this use case. If I understand your previous mail the 
> solution would me "Hex editing manually the Xen binary to set the early 
> printk", right? If so, you are assuming that the distro (or anything 
> else) is proving the zImage. Otherwise the developper has to:
>     - unpack from the uImage
>     - editing the zImage
>     - recreate the uImage

No distro would ship the actual uImage, it's too machine specific.

I would expect this to be used by running:
        xen-enable-early-printk /boot/xen midway

where xen-enable-early-printk is a simple tool we provide.

Then if a uIamge is then required then this would be generated by
whatever distro tooling would have generated it in the non-early-printk
case, by rerunning that tool.

> That seems very complicated compare to recompiling Xen...

Not really and this isn't so much for developers, but for users with
access to problematic systems to provide us with information.

Ian.



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel