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Date:   Tue, 21 Aug 2018 11:02:51 -0700
From:   Frank Rowand <frowand.list@...il.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        DTML <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] scripts/dtc: consolidate include path options in Makefile

On 08/21/18 00:18, Masahiro Yamada wrote:
> Hi Frank,
> 
> 
> 2018-08-21 14:37 GMT+09:00 Frank Rowand <frowand.list@...il.com>:
>> On 08/20/18 19:08, Masahiro Yamada wrote:
>>> Hi Frank,
>>>
>>> 2018-08-21 10:31 GMT+09:00 Frank Rowand <frowand.list@...il.com>:
>>>> On 08/20/18 14:32, Rob Herring wrote:
>>>>> On Mon, Aug 20, 2018 at 1:55 PM Frank Rowand <frowand.list@...il.com> wrote:
>>>>>>
>>>>>> On 07/03/18 18:59, Masahiro Yamada wrote:
>>>>>>> It is tedious to specify extra compiler options for every file.
>>>>>>> HOST_EXTRACFLAGS is useful to add options to all files in a
>>>>>>> directory.
>>>>>>>
>>>>>>> -I$(src)/libfdt is needed for all the files in this directory
>>>>>>> to include libfdt_env.h etc. from scripts/dtc/libfdt/.
>>>>>>>
>>>>>>> On the other hand, -I$(src) is used to include check-in headers
>>>>>>> from generated C files.  Thus, I added it only to dtc-lexer.lex.o
>>>>>>> and dtc-parser.tab.o .
>>>>>>>
>>>>>>> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>>>>>>> ---
>>>>>>>
>>>>>>>  scripts/dtc/Makefile | 18 ++++--------------
>>>>>>>  1 file changed, 4 insertions(+), 14 deletions(-)
>>>>>>>
>>>>>>> diff --git a/scripts/dtc/Makefile b/scripts/dtc/Makefile
>>>>>>> index 9cac65b..1c943e0 100644
>>>>>>> --- a/scripts/dtc/Makefile
>>>>>>> +++ b/scripts/dtc/Makefile
>>>>>>> @@ -9,21 +9,11 @@ dtc-objs    := dtc.o flattree.o fstree.o data.o livetree.o treesource.o \
>>>>>>>  dtc-objs     += dtc-lexer.lex.o dtc-parser.tab.o
>>>>>>>
>>>>>>>  # Source files need to get at the userspace version of libfdt_env.h to compile
>>>>>>> +HOST_EXTRACFLAGS := -I$(src)/libfdt
>>>>>>
>>>>>> Shouldn't that be += instead of :=?
>>>>>
>>>>> I don't think so. The definition is local to the file (and reset
>>>>> before each makefile is included).
>>>>>
>>>>> Rob
>>>>>
>>>>
>>>> Every other place where HOST_EXTRACFLAGS is assigned a value, += is used
>>>> instead of :=, including the example in Documentation/kbuild/makefiles.txt
>>>>
>>>> What makes scripts/dtc/Makefile different than the other makefiles?
>>>>
>>>> -Frank
>>>>
>>>
>>>
>>> := and += work in the same way in here.
>>
>> Unless I do: HOST_EXTRACFLAGS=xxx make
>> where "xxx" is some random flag I feel like adding in a particular build.
> 
> 
> 
> This is not the intended usage of HOST_EXTRACFLAGS.

I seem to have found a useful feature for making a specific object in a
development context with additional compiler flags.  But a feature that
you say is not intended.

I do understand that there is an intended difference between HOSTCFLAGS
and HOST_EXTRACFLAGS.  But I do not agree that using HOST_EXTRACFLAGS
on the make commandline when building a single object in a development
context is abuse.


> HOST_EXTRACFLAGS is supposed to be set by Makefile in the kernel tree.

But it is not set, thus it is currently available (and has been for many
years) for the usage that I specified above.


> Documentation/kbuild/makefiles.txt explains this:
> 
>        To set flags that will take effect for all host programs created
>        in that Makefile, use the variable HOST_EXTRACFLAGS.
> 
> 
> 
> If you want to pass additional host compiler flags,
> please use HOSTCFLAGS instead.

That will not work because the top level Makefile has:

   HOSTCFLAGS   := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \


> Documentation/kbuild/kbuild.txt lists officially supported
> environment variables / command line variables.> 
>     HOSTCFLAGS
>     --------------------------------------------------
>     Additional flags to be passed to $(HOSTCC) when building host programs.

HOSTCFLAGS is not in my 4.18.0 Documentation/kbuild/kbuild.txt.  What version are
you looking at?

  $ git log -n1
  commit 94710cac0ef4ee177a63b5227664b38c95bbf703
  Author: Linus Torvalds <torvalds@...ux-foundation.org>
  Date:   Sun Aug 12 13:41:04 2018 -0700

      Linux 4.18
  $ git grep HOSTCFLAGS Documentation/kbuild/kbuild.txt
  $


But this is where I concede that HOST_EXTRACFLAGS is also not listed as
an officially supported environment variable or command line variable.  I
had not checked here for that limitation.


> 
> 
> Maybe I should add
> 
> HOST_EXTRACFLAGS   :=
> HOST_EXTRACXXFLAGS :=
> 
> to the top of scripts/Makefile.build
> to reset the variables explicitly
> in case people try to abuse them.

Yes, if you intend that it not be possible to initialize them in the make
command then you should initialize them.  If you do that, it is easy
enough for me to patch the initialization out in cases where I want the
extra functionality.


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