linux-kernel - Re: [PATCH V7] kbuild: create a rule to run the pre-processor on *.dts files

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Date:	Fri, 01 Feb 2013 10:27:30 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Rob Herring <robherring2@...il.com>
CC:	srinivas.kandagatla@...com, Grant Likely <glikely@...retlab.ca>,
	Michal Marek <mmarek@...e.cz>,
	Stephen Warren <swarren@...dia.com>,
	Sam Ravnborg <sam@...nborg.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	linux-kernel@...r.kernel.org, Scott Wood <scottwood@...escale.com>,
	devicetree-discuss@...ts.ozlabs.org
Subject: Re: [PATCH V7] kbuild: create a rule to run the pre-processor on
 *.dts files

On 02/01/2013 09:51 AM, Rob Herring wrote:
> On 02/01/2013 03:01 AM, Srinivas KANDAGATLA wrote:
>> Hi Stephen,
>> Not sure if you have already noticed this but,
>> I did try this patch on my 3.8, and it looks like the intermediate dts
>> file replaces all instances of linux with 1 because of predefined macros
>> in gcc.
>> As a result
>>     linux,stdout-path = "/soc/stm-asc2";
>> is changed to.
>>     1,stdout-path = "/soc/stm-asc2";
>>
>> On my version of compiler(gcc version 4.6.3) I have
>>
>> armv7-linux-gcc -E -dM - < /dev/null | grep -v _
>> #define unix 1
>> #define linux 1
>>
>> Which might be true with most compiler versions aswell.
>> As we are using linux as prefix for some device tree properties it makes
>> sense to undef the linux gcc define.
>> Adding -Ulinux to cmd_dtc_cpp should fix it.
>>
>> -cmd_dtc_cpp = $(CPP) $(cpp_flags) -D__DTS__ -x assembler-with-cpp -o
>> $(dtc-tmp) $< ; \
>> +cmd_dtc_cpp = $(CPP) $(cpp_flags) -D__DTS__  -Ulinux -x
>> assembler-with-cpp -o $(dtc-tmp) $< ; \
>>     $(objtree)/scripts/dtc/dtc -O dtb -o $@ -b 0 $(DTC_FLAGS) $(dtc-tmp)
> 
> That's a hackish solution that seems fragile as well. Is there no way to
> turn off all built-in defines?

I'm pretty sure there is; I'll go find it.

But we do want to keep some of the built-in defines. for example, -x
assembler-with-cpp turns on __ASSEMBLY__ or similar, which headers can
use to determine whether to only set up #defines, or also C-oriented
stuff like types/prototypes. So, at least that one would need to be
explicitly re-defined.

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