On 18.10.21 12:36, Jan Beulich wrote:
> On 18.10.2021 12:28, Juergen Gross wrote:
>> 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"
> 
> I fully agree, yet ...
> 
>> 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.
> 
> ... developers' habits would only be my second concern here (and if that
> had been the only one, then I would not see this as a reason speaking
> against the change, but as said I've never been building from the root,
> and I've also been building sort of out-of-tree all the time). Yet while
> writing this reply I came to realize that my primary concern was wrong:
> People would not need to adjust their spec files (or alike), at least
> not as long as they consume only files living under dist/.
> 
> So, Anthony - thoughts about making the default in-tree Xen build
> actually build into, say, build/xen/?

Or maybe even build-<arch>[-debug]/xen/?


Juergen