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

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

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.

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).