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

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Date:	Thu, 20 Feb 2014 13:53:41 +0100
From:	Richard Weinberger <richard.weinberger@...il.com>
To:	Markos Chandras <Markos.Chandras@...tec.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 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.

-- 
Thanks,
//richard
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