On 18.10.21 11:51, Anthony PERARD wrote:
> On Mon, Oct 18, 2021 at 11:02:20AM +0200, Jan Beulich wrote:
>> On 15.10.2021 18:58, Anthony PERARD wrote:
>>> On Thu, Oct 14, 2021 at 12:14:29PM +0200, Jan Beulich wrote:
>>>> On 24.08.2021 12:50, Anthony PERARD wrote:
>>>>> --- a/xen/Rules.mk
>>>>> +++ b/xen/Rules.mk
>>>>> @@ -38,7 +38,7 @@ SPECIAL_DATA_SECTIONS := rodata $(foreach a,1 2 4 8 16, \
>>>>>                            $(foreach r,rel rel.ro,data.$(r).local)
>>>>>   
>>>>>   # The filename build.mk has precedence over Makefile
>>>>> -mk-dir := $(src)
>>>>> +mk-dir := $(srctree)/$(src)
>>>>>   include $(if $(wildcard $(mk-dir)/build.mk),$(mk-dir)/build.mk,$(mk-dir)/Makefile)
>>>>
>>>> Perhaps already when it was changed to $(src) the name has become
>>>> slightly misleading, at least imo: I would rather expect a variable
>>>> with this name to refer to the build dir/tree. Maybe "srcdir" or
>>>> even shorted "sd" right from the start? (Reaching here I can finally
>>>> see why having a shorthand is helpful.)
>>>
>>> I have to think about that. I've made some further progress in order to
>>> be able to build the Xen pvhshim without a link farm and notice that
>>> nearly every source file needs to use "$(srctree)/$(src)"
>>
>> Oh, now I'm curious as to the why here. I thought use of $(srctree)
>> ought to be the exception.
> 
> In Linux, the use of $(srctree) is indeed the exception. This is because
> we have VPATH=$(srctree), so when `make` look for a prerequisite or a
> target it will look first in the current directory and then in
> $(srctree). That works fine as long as the source tree only have sources
> and no built files.
> 
> But if we want to be able to build the pv-shim without the linkfarm and
> thus using out-of-tree build, we are going to need the ability to build
> from a non-clean source tree. I don't think another way is possible.

Is there any reason (apart from historical ones) to build the hypervisor
in $(srctree)?

I could see several advantages to build it in another directory as soon
as the build system has this capability:

- possibility to have a simple build target for building multiple archs
   (assuming the cross-tools are available), leading to probably less
   problems with breaking the build of "the other" architecture we are
   normally not working with (and in future with e.g. Risc-V being added
   this will be even more important)

- possibility to have a debug and a non-debug build in parallel (in fact
   at least at SUSE we are working around that by building those with an
   intermediate "make clean" for being able to package both variants)

- make clean for the hypervisor part would be just a "rm -r"

Yes, this would require us (the developers) to maybe change some habits,
but I think this would be better than working around the issues by
adding $(srctree) all over the build system.


Juergen