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Date: Thu, 10 Feb 2011 15:35:09 +0100
From: Michal Marek <mmarek@suse.cz>
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Subject: Re: arch/x86/Makefile kbuild problem
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To: Philippe Auphelle <pauphelle@gmail.com>
Cc: linux-kbuild@vger.kernel.org

On 24.1.2011 11:35, Philippe Auphelle wrote:
> Hi All,
> 
> Building an x86_64 external module from an x86 (32-bit) Linux 2.6.35,
> I get a "stack protector enabled but no compiler support" error.
> I'm by no way a kbuild (or even make) specialist, but it looks to me
> like the problem is this:
> 
> The error is produced in arch/x86/Makefile, line 81.
> 
> Looking further, it looks like this code relies on $(biarch) being set
> to the CC bitness parm (-m32 / -m64) to call the cc_has_sp detection
> script (line 77).
> Problem is, $(biarch) is only set (to -m32) when CONFIG_X86_32 is set
> (line 20), but *not* when the else clause is taken (-m64 option is
> directly set then in KBUILD_AFLAGS and KBUILD_CFLAGS then, (lines
> 49-50) ).
> As a result, the detection scripts always fails.
> 
> replacing lines 49-50 by something like:
>         biarch := $(call cc-option,-m64)
>         KBUILD_AFLAGS += $(biarch)
>         KBUILD_CFLAGS += $(biarch)

I think you can omit the cc-option call and simply set biarch := -m64,
because the gcc x86_64 target always had the -m64 option.
> 
> solves the problem.
> 
> I just checked with the latest 2.6.37, and arch/x86/Makefile hasn't
> changed since 2.6.35 (at least not in that part of the file).
> 
> Questions are:
> - Could someone more knowledgeable than me in that matter be kind
> enough to confirm that this is truely the problem (and a valid
> solution)?
> and if so,
> - Is this the right place to report it to get it eventually fixed?
> (and if it ain't, where should it be?)

You should send a proper patch (refer to
Documentation/SubmittingPatches) to lkml and the people under the "X86
ARCHITECTURE (32-BIT AND 64-BIT)" entry in the MAINTAINERS file.

Michal