Re: [Qemu-devel] [PATCH 01/20] Makefile: Allow CPU targets to reside in target/ folder, too

[David Gibson]

On Sat, Dec 10, 2016 at 11:59:09AM +0100, Laurent Vivier wrote:
> Le 09/12/2016 à 17:51, Thomas Huth a écrit :
> > On 09.12.2016 13:24, Laurent Vivier wrote:
> >> Le 09/12/2016 à 13:17, Thomas Huth a écrit :
> >>> To be able to compile the CPU targets from within a subfolder
> >>> of the target/ folder, we've got to adapt the Makefile.target
> >>> a little bit first. After this change, target CPUs can either
> >>> reside in a target/xxx folder or continue to use the target-xxx
> >>> scheme. The latter will be disabled once all targets have been
> >>> moved.
> >>>
> >>> Signed-off-by: Thomas Huth <address@hidden>
> >>> ---
> >>>  Makefile.target | 10 ++++++++--
> >>>  1 file changed, 8 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/Makefile.target b/Makefile.target
> >>> index 7a5080e..90b25ae 100644
> >>> --- a/Makefile.target
> >>> +++ b/Makefile.target
> >>> @@ -7,11 +7,17 @@ include config-target.mak
> >>>  include config-devices.mak
> >>>  include $(SRC_PATH)/rules.mak
> >>>  
> >>> +ifneq ($(wildcard $(SRC_PATH)/target/$(TARGET_BASE_ARCH)),)
> >>> +TARGET_FOLDER=target/$(TARGET_BASE_ARCH)
> >>> +else
> >>> +TARGET_FOLDER=target-$(TARGET_BASE_ARCH)
> >>> +endif
> >>
> >> Perhaps you should consider to use ':=' instead of '='.
> > 
> > Most of the other variables in that file seem to be set with '=' instead
> > of ':=', so using '=' sounds more consistent to me ... is there a real
> > benefit of using ':=' here?
> 
> With ':=' your variable is expanded once, with '=' it is expanded
> whenever it is used. I think this is not needed in your case.
> 
> https://www.gnu.org/software/make/manual/html_node/Flavors.html#Flavors

I tend to thing '=' is the safer default option unless you're really
hitting performance problems that ':=' can alleviate.  Not
re-expanding can lead to confusing bugs later if the definition is
changed so that re-expansion matters in future.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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