linux-kernel - Re: arch/x86//kernel/ftrace.c:35:3: error: #error The following combination is not supported: ((compiler missing -mfentry) || (CONFIG_X86_32 and !CONFIG_DYNAMIC_FTRACE)) && CONFIG_FUNCTION_GRAPH_TRACER && CONFIG_CC_OPTIMIZE_FOR

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Date:   Mon, 17 Apr 2017 08:33:13 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     kbuild test robot <fengguang.wu@...el.com>
Cc:     kbuild-all@...org, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: arch/x86//kernel/ftrace.c:35:3: error: #error The following
 combination is not supported: ((compiler missing -mfentry) || (CONFIG_X86_32
 and !CONFIG_DYNAMIC_FTRACE)) && CONFIG_FUNCTION_GRAPH_TRACER &&
 CONFIG_CC_OPTIMIZE_FOR_SIZE

On Sun, Apr 16, 2017 at 09:20:50AM +0800, kbuild test robot wrote:
> Hi Josh,
> 
> FYI, the error/warning still remains.
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   d5ff0814fda50f0306e102f39640cf5bb76af08e
> commit: 3f135e57a4f76d24ae8d8a490314331f0ced40c5 x86/build: Mostly disable '-maccumulate-outgoing-args'
> date:   2 weeks ago
> config: x86_64-randconfig-s1-04160822 (attached as .config)
> compiler: gcc-4.4 (Debian 4.4.7-8) 4.4.7
> reproduce:
>         git checkout 3f135e57a4f76d24ae8d8a490314331f0ced40c5
>         # save the attached .config to linux build tree
>         make ARCH=x86_64 
> 
> All errors (new ones prefixed by >>):
> 
> >> arch/x86//kernel/ftrace.c:35:3: error: #error The following combination is not supported: ((compiler missing -mfentry) || (CONFIG_X86_32 and !CONFIG_DYNAMIC_FTRACE)) && CONFIG_FUNCTION_GRAPH_TRACER && CONFIG_CC_OPTIMIZE_FOR_SIZE

Hi Fengguang,

The error is working as designed.  gcc < 4.6.0 doesn't have -mfentry, so
it fails the above check on x86.  Can you add a skip rule?  It should
skip building the following case:

  x86 && ((gcc < 4.6.0) || (CONFIG_X86_32 and !CONFIG_DYNAMIC_FTRACE)) && CONFIG_FUNCTION_GRAPH_TRACER && CONFIG_CC_OPTIMIZE_FOR_SIZE

-- 
Josh