Re: [PATCH] build: convert CONFIG_COMPAT to Kconfig

From: Doug Goldstein <cardoe@cardoe.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>, xen-devel@lists.xen.org
Cc: Keir Fraser <keir@xen.org>, Jan Beulich <jbeulich@suse.com>
Subject: Re: [PATCH] build: convert CONFIG_COMPAT to Kconfig
Date: Sun, 20 Dec 2015 07:42:15 -0600	[thread overview]
Message-ID: <5676B037.1070405@cardoe.com> (raw)
In-Reply-To: <5674840E.4020101@citrix.com>

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On 12/18/15 4:09 PM, Andrew Cooper wrote:
> On 18/12/2015 21:49, Doug Goldstein wrote:
>> On 12/18/15 3:35 PM, Andrew Cooper wrote:
>>> On 18/12/2015 20:06, Doug Goldstein wrote:
>>>> Use the Kconfig generated CONFIG_COMPAT defines in the code base.
>>>>
>>>> CC: Keir Fraser <keir@xen.org>
>>>> CC: Jan Beulich <jbeulich@suse.com>
>>>> CC: Andrew Cooper <andrew.cooper3@citrix.com>
>>>> Signed-off-by: Doug Goldstein <cardoe@cardoe.com>
>>> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>, although I have
>>> a slight quibble.
>>>
>>>> ---
>>>> This was previously Acked-by: Jan Beulich <jbeulich@suse.com> but then
>>>> there was a request to change it to xen/common/Kconfig from
>>>> xen/arch/x86/Kconfig. Unfortunately a small typo ('def_bool y' instead of
>>>> 'bool') caused it to break on ARM. This resolves the issue and should be
>>>> ready to merge.
>>>> ---
>>>>  config/x86_64.mk     | 1 -
>>>>  xen/arch/x86/Kconfig | 1 +
>>>>  xen/common/Kconfig   | 7 +++++++
>>>>  3 files changed, 8 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/config/x86_64.mk b/config/x86_64.mk
>>>> index f12d549..85fa27c 100644
>>>> --- a/config/x86_64.mk
>>>> +++ b/config/x86_64.mk
>>>> @@ -2,7 +2,6 @@ CONFIG_X86 := y
>>>>  CONFIG_X86_64 := y
>>>>  CONFIG_X86_$(XEN_OS) := y
>>>>  
>>>> -CONFIG_COMPAT := y
>>>>  CONFIG_MIGRATE := y
>>>>  CONFIG_XCUTILS := y
>>>>  
>>>> diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
>>>> index 07e366d..7d2ed96 100644
>>>> --- a/xen/arch/x86/Kconfig
>>>> +++ b/xen/arch/x86/Kconfig
>>>> @@ -3,6 +3,7 @@ config X86_64
>>>>  
>>>>  config X86
>>>>  	def_bool y
>>>> +	select COMPAT
>>>>  	select HAS_ACPI
>>>>  	select HAS_CPUFREQ
>>>>  	select HAS_EHCI
>>>> diff --git a/xen/common/Kconfig b/xen/common/Kconfig
>>>> index 7d0e9a9..046e257 100644
>>>> --- a/xen/common/Kconfig
>>>> +++ b/xen/common/Kconfig
>>>> @@ -1,6 +1,13 @@
>>>>  
>>>>  menu "Common Features"
>>>>  
>>>> +config COMPAT
>>>> +	bool
>>>> +	help
>>>> +	  32-bit interface support on 64-bit Xen which is used for both
>>>> +	  HVM and PV guests. HVMLoader makes 32-bit hypercalls irrespective
>>>> +	  of the destination runmode of the guest.
>>> As this is now common, probably want to specify x86 HVM and PV guests. 
>>> Arm guests are technically HVM, although the term is rather less common
>>> on their side.
>>>
>>> ~Andrew
>>>
>> How about:
>>
>> 32-bit interface support on 64-bit Xen which is used by x86 HVM and PV
>> guests and ARM HVM guests. The reason this is used for HVM guests is
>> that HVMLoader makes 32-bit hypercalls irrespective of the destination
>> run mode of the guest.
>>
> 
> The complication here is that arm doesn't yet support compat.  There is
> a hope to (which is, I guess, why Jan asked for it to be common), but it
> shouldn't give any implication that it is available on ARM yet.

So maybe just drop the "and ARM HVM guests" part of that statement and
when that gets added we can expand the language?

> 
> I am not overly familiar with the kconfig grammar.  Is there a sensible
> way to limit the option to being visible only on x86, and only on 64bit
> builds?  (even if arm supported compat, it wouldn't make sense to offer
> it to arm32).
> 
> Or am I just talking my way back around to suggesting that it be an arch
> specific option?
> 
> ~Andrew
> 

Not necessarily. Currently its not visible to users at all and x86 just
enables it. Should it be made to be visible we could keep it in the
common place and add depends like "depends on X86_64" or "depends on
64BIT" (both x86_64 and arm64).

-- 
Doug Goldstein

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