linux-kernel - Re: [PATCH] Makefile: Unset stack-protector gcc flag if it is not supported

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Message-ID: <530608E0.90805@imgtec.com>
Date:	Thu, 20 Feb 2014 13:53:36 +0000
From:	Markos Chandras <Markos.Chandras@...tec.com>
To:	Richard Weinberger <richard.weinberger@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>, Michal Marek <mmarek@...e.cz>,
	<linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH] Makefile: Unset stack-protector gcc flag if it is not
 supported

On 02/20/2014 12:53 PM, Richard Weinberger wrote:
> On Thu, Feb 20, 2014 at 1:46 PM, Markos Chandras
> <Markos.Chandras@...tec.com> wrote:
>> On 02/07/2014 05:15 PM, Markos Chandras wrote:
>>>
>>> In case the compiler does not support the stack-protector option,
>>> unset the flag to avoid build failures. Printing a warning is enough
>>> to let the user know that this flag will not be used.
>>> Fixes the following build problem when using a toolchain which does
>>> not support the -fstack-protector-strong flag:
>>>
>>> Makefile:614: Cannot use CONFIG_CC_STACKPROTECTOR_STRONG:
>>> -fstack-protector-strong not supported by compiler
>>> mips-linux-gnu-gcc: error: unrecognized command line option
>>> '-fstack-protector-strong'
>>> scripts/Makefile.build:308: recipe for target 'scripts/mod/empty.o' failed
>>> make[2]: *** [scripts/mod/empty.o] Error 1
>>> make[2]: *** Waiting for unfinished jobs....
>>> scripts/Makefile.build:455: recipe for target 'scripts/mod' failed
>>>
>>> Cc: Michal Marek <mmarek@...e.cz>
>>> Cc: linux-kbuild@...r.kernel.org
>>> Signed-off-by: Markos Chandras <markos.chandras@...tec.com>
>>> ---
>>>    Makefile | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/Makefile b/Makefile
>>> index 606ef7c..63a5333 100644
>>> --- a/Makefile
>>> +++ b/Makefile
>>> @@ -607,12 +607,14 @@ ifdef CONFIG_CC_STACKPROTECTOR_REGULAR
>>>      ifeq ($(call cc-option, $(stackp-flag)),)
>>>        $(warning Cannot use CONFIG_CC_STACKPROTECTOR: \
>>>                -fstack-protector not supported by compiler))
>>> +    stackp-flag :=
>>>      endif
>>>    else ifdef CONFIG_CC_STACKPROTECTOR_STRONG
>>>      stackp-flag := -fstack-protector-strong
>>>      ifeq ($(call cc-option, $(stackp-flag)),)
>>>        $(warning Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: \
>>>                -fstack-protector-strong not supported by compiler)
>>> +    stackp-flag :=
>>>      endif
>>>    else
>>>      # Force off for distro compilers that enable stack protector by
>>> default.
>>>
>>
>> Ping again?
>
> This is by design. We want the build fail if
> CONFIG_CC_STACKPROTECTOR_STRONG is set
> but the toolchain does not support it.
> Otherwise we could end up with a kernel without stackprotector even if
> the config symbol is set.
>

Hi Richard,

Then maybe the $(warning...) should be converted to $(error...)?
Because it's not really a warning if the build failure is expected to 
happen.

-- 
markos

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