Re: [Xen-devel] [PATCH] xen/doc: remove obsolete warning about testing gcov on arm

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 7/9/19 6:05 PM, Viktor Mitin wrote:
> On Tue, Jul 9, 2019 at 3:11 PM Julien Grall <julien.grall@xxxxxxx> wrote:
> > Hi,
> Hi Julien,
>
> > On 7/9/19 11:56 AM, Viktor Mitin wrote:
> > > Remove obsolete warning about testing gcov on arm.
> > > gcov has been fixed and tested with arm hw previously
> > >
> > > See commit 6ac66c9
> > This commit...
> >
> > > Signed-off-by: Viktor Mitin <viktor_mitin@xxxxxxxx>
> > > ---
> > >    docs/hypervisor-guide/code-coverage.rst | 7 -------
> > >    1 file changed, 7 deletions(-)
> > >
> > > diff --git a/docs/hypervisor-guide/code-coverage.rst 
> > > b/docs/hypervisor-guide/code-coverage.rst
> > > index 3cebf2d96e..947ee48701 100644
> > > --- a/docs/hypervisor-guide/code-coverage.rst
> > > +++ b/docs/hypervisor-guide/code-coverage.rst
> > > @@ -6,13 +6,6 @@ the coverage of its own basic blocks.  Being a piece of system 
> > > software rather
> > >    than a userspace, it can't automatically write coverage out to the 
> > > filesystem,
> > >    so some extra steps are required to collect and process the data.
> > >
> > > -.. warning::
> > > -
> > > -  Coverage has only been tested on x86 at the moment.  ARM doesn't currently
> > > -  boot when the final binary exceeds 2MB in size, and the coverage build tends
> > > -  to exceeds this limit.
> > ... does not address the 2MB part. So part of the warning is still valid
> > here.
> Is it known why do we have this 2MB limit?
Without code coverage (and UBSAN) Xen is quite small and can fit in 2MB.

The memory layout is fixed, so we had to define a maximum size. 2MB is 
convenient because you only deal with only a second-level page-table entry.
> Should we fix it?
It should be fixed but not very easy with the current boot code. I am in 
process to rework the boot/memory code (see [1]). There are more to come.
Once the work is finished, it should be easy to extend the limit to 4MB 
(or bigger if necessary).
Cheers,

[1] https://lists.xen.org/archives/html/xen-devel/2019-06/msg00588.html

--
Julien Grall

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