[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

On 20/02/14 11:20, Ian Campbell wrote:
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

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.

And a similar one to disable, I guess.

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.

Sounds good. Do you plan to work on it?

It would be nice to have this item on the ARM todo page.

Julien Grall

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.