Re: [Qemu-devel] [Qemu-trivial] [PATCH] Makefile: fix out-of-tree builds

[Michael Roth <mdroth@linux.vnet.ibm.com>]

On 07/25/2011 09:43 AM, Stefan Hajnoczi wrote:
> On Mon, Jul 25, 2011 at 2:57 PM, Michael Roth<mdroth@linux.vnet.ibm.com>  wrote:
>> On 07/25/2011 07:43 AM, Stefan Hajnoczi wrote:
>>>
>>> On Mon, Jul 25, 2011 at 1:16 PM, Michael Roth<mdroth@linux.vnet.ibm.com>
>>>   wrote:
>>>>
>>>> On 07/25/2011 05:15 AM, Stefan Hajnoczi wrote:
>>>>>
>>>>> On Thu, Jul 21, 2011 at 5:41 AM, Alexandre Raymond<cerbere@gmail.com>
>>>>>   wrote:
>>>>>>
>>>>>> This patch fixes a minor bugs which prevented QEMU from being built
>>>>>> out of tree.
>>>>>>
>>>>>> Signed-off-by: Alexandre Raymond<cerbere@gmail.com>
>>>>>> ---
>>>>>>   Makefile |    2 +-
>>>>>>   1 files changed, 1 insertions(+), 1 deletions(-)
>>>>>
>>>>> I don't normally use --source-path but it still seems broken to me
>>>>> after applying your patch?
>>>>>
>>>>> $ cd /tmp; mkdir out; cd out
>>>>> $ ~/qemu/configure --source-path=$HOME/qemu
>>>>> $ make
>>>>>    GEN   config-all-devices.mak
>>>>> cat: i386-softmmu/config-devices.mak: No such file or directory
>>>>> cat: x86_64-softmmu/config-devices.mak: No such file or directory
>>>>> cat: alpha-softmmu/config-devices.mak: No such file or directory
>>>>>
>>>>> Stefan
>>>>>
>>>>
>>>> Works okay for me with and without the patch if I do a `make distclean`
>>>> in
>>>> $HOME/qemu beforehand.
>>>>
>>>> Not sure what the trigger is for the breakage Alexandre is trying to
>>>> address.
>>>
>>> You are right that make distclean in the source directory solves the
>>> issue.
>>>
>>> Intuitively I expect ./configure to re-wire things, make distclean
>>> should not be necessary.
>>>
>>> Alexandre: Can you describe the case where you hit a build issue in more
>>> detail?
>>>
>>> Stefan
>>
>> The root problem seems to be that by including $(SRC_DIR) in VPATH (via
>> $(call set-vpath, $(SRC_PATH):$(SRC_PATH)/hw)), $(SRC_DIR) ends up being
>> searched for source files as well as target dependencies. So any crud left
>> in there can still satisfy dependencies when building outside $SRC_PATH. I'm
>> not sure there's a simple way around this except to prefix all source files
>> with $(SRC_PATH) and remove $(SRC_PATH) from VPATH...I'm not even sure that
>> would work though..
>>
>> Perhaps just a friendly error message if we detect the $(SRC_PATH) directory
>> needs a distclean? Once you know that's the magic fix it's not terribly
>> inconvenient....alternatively we could automatically do the distclean in
>> $SRC_PATH but that might be considered overstepping our bounds.
>
> Yes, ./configure could detect the case where --source-path= is used
> but the source tree has build outputs.
>
>> Consequently, it seems like this patch would be a noop...default-configs
>> should never exist in an external build directory, so
>> $(SRC_PATH)/default-configs and default-configs end up being equivalent when
>> make eventually find it in $(SRC_PATH).
>
> Thanks for finding out what is happening.  My understanding is that
> $(SRC_PATH) must be used when invoking external commands during the
> build, since they don't perform vpath search.  For make targets we
> don't need to use $(SRC_PATH) since the vpath is in effect.

Ah, yah my mistake, patch would still have some effect.

>
> Stefan