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:   Tue, 18 Apr 2017 11:52:41 -0700
From:   Andi Kleen <andi@...stfloor.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     kbuild test robot <fengguang.wu@...el.com>, 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

Josh Poimboeuf <jpoimboe@...hat.com> writes:
>
> 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

This will also break everyone's randconfig builds. The better way
would be to check this in the Makefile and disable one of the options

-Andi