linux-kernel - Re: [PATCH trace-cmd 3/3] Revert "trace-cmd: Use conditional assignment of CC and AR"

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Message-ID: <AANLkTikHy1pZP0=cpmSD_HG-jeJvgne3u2ivOif6DHP8@mail.gmail.com>
Date:	Wed, 9 Mar 2011 18:27:35 -0800
From:	David Sharp <dhsharp@...gle.com>
To:	Darren Hart <dvhart@...ux.intel.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	mrubin@...gle.com
Subject: Re: [PATCH trace-cmd 3/3] Revert "trace-cmd: Use conditional
 assignment of CC and AR"

On Wed, Mar 9, 2011 at 5:58 PM, Darren Hart <dvhart@...ux.intel.com> wrote:
> On 03/09/2011 05:36 PM, Steven Rostedt wrote:
>> On Wed, 2011-03-09 at 17:27 -0800, Darren Hart wrote:
>>> On 03/09/2011 03:58 PM, David Sharp wrote:
>>>>
>>>> This reverts commit 6c696cec3f264a9399241b6e648f58bc97117d49.
>>>>
>>>> Make has default values CC and AR of 'cc' and 'ar' respectively. This
>>>> means
>>>> that "CC ?= anything" will never have effect, because CC is always
>>>> already set.
>>>> Because of this, 6c696cec makes setting CROSS_COMPILE from the command
>>>> line or
>>>> environment useless.
>>>
>>> The problem with this approach is it prevents the user from setting CC
>>> explicitly with the environment which is a very common way of using a
>>> specific version of gcc (for example). It also places restrictions on
>>> the filename of the compiler (it must end in gcc - so gcc-4.5.1 cannot
>>> work), this isn't acceptable.
>>>
>>> You could use CC=your-cross-compiler, and if that doesn't work for you,
>>> you could prepare a patch that conditionally sets CC only if
>>> CROSS_COMPILE is set, but please do not simply revert this patch which
>>> solved a real problem with the Makefile.
>>
>> Hmm, but the thing is, the change did not work,
>
> It did work for me as I was setting CC= on the command line.
>
> unless your environment
>>
>> for some reason does not supply a 'cc'. Or that 'cc' defaulted to the
>> compiler that you wanted, where 'gcc' would not.
>>
>> Thus, would you be fine with something like:
>>
>>        BUILD_CC ?=     $(CROSS_COMPILE)gcc
>>        CC       =      $(BUILD_CC)
>
> This would also work, but what is wrong with:
>
> dvhart@...bt:templates$ cat Makefile
> ifdef CROSS_COMPILE
> CC = $(CROSS_COMPILE)gcc
> AR = $(CROSS_COMPILE)ar
> endif
>
> all:
>        echo "CC: $(CC)"
>
> dvhart@...bt:templates$ make -s
> CC: cc
>
> dvhart@...bt:templates$ CC=gcc-4.5.1 make -s
> CC: gcc-4.5.1
>
> dvhart@...bt:templates$ CROSS_COMPILE=my-cross- make -s
> CC: my-cross-gcc
>
>
> Seems to meet everyone's needs without changing any tools/scripts/etc that
> have used trace-cmd before or after the CC ?= wreckage.

It's a little odd that the default CC is "cc" unless you supply
CROSS_COMPILE, then it's "gcc". I'd probably be okay with this, but I
would think it's weird.

I don't know the answers, but if we take the kernel Makefile as a
template, then setting CC doesn't work.

>
>
>
> Thanks,
>
> --
> Darren
>
>>
>> Then you could just update BUILD_CC and that will update CC for you.
>>
>> -- Steve
>>
>>
>
>
> --
> Darren Hart
> Intel Open Source Technology Center
> Yocto Project - Linux Kernel
>
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