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Date: Wed, 26 Sep 2018 12:37:44 -0500
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe LEROY <christophe.leroy@c-s.fr>
Cc: Russell Currey <ruscur@russell.cc>,
 Benjamin Herrenschmidt <benh@kernel.crashing.org>,
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 Andrew Donnellan <andrew.donnellan@au1.ibm.com>,
 linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 2/2] powerpc/64: add stack protector support
Message-ID: <20180926173744.GN23155@gate.crashing.org>
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On Wed, Sep 26, 2018 at 11:41:26AM +0200, Christophe LEROY wrote:
> Le 26/09/2018 à 11:28, Segher Boessenkool a écrit :
> >On Wed, Sep 26, 2018 at 09:58:30AM +0200, Christophe LEROY wrote:
> >>Segher, any idea about this problem ?
> >
> >>>>arch/powerpc/platforms/powermac/bootx_init.o: In function 
> >>>>`bootx_printf':
> >>>>/var/lib/jenkins-slave/workspace/snowpatch/snowpatch-linux-
> >>>>sparse/linux/arch/powerpc/platforms/powermac/bootx_init.c:88:
> >>>>undefined reference to `__stack_chk_fail_local'
> >
> >Are you building as PIC?  Are you linking libssp_nonshared.a?  Why not?
> 
> Spotted, thanks.
> 
> arch/powerpc/platforms/powermac/Makefile contains:
> 
> CFLAGS_bootx_init.o  		+= -fPIC
> 
> Does it mean we should add -lssp_nonshared to LDFLAGS_vmlinux ?

Something like that.

> Or maybe stack protection on bootx_init doesn't make much sense and we 
> could just do the following ?
> 
> CFLAGS_bootx_init.o  		+= -fPIC $(call cc-option, 
> -fno-stack-protector)

But more likely this.  Why does it use -fPIC?

If it is only boot-time init (which the name suggests) then disabling
ssp makes a lot of sense.


Segher