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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>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        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>
References: <2b934594d21ade67a4092637cf9e6b7d2d131187.1537801613.git.christophe.leroy@c-s.fr> <e84d65fb4744cf8260eb2fc9474765a7f3a60573.1537801613.git.christophe.leroy@c-s.fr> <0797fc91-6400-2508-1cc0-4bba78aafbbb@c-s.fr> <d203ccfce64c8f9fd403162f2fa3807ade7f1d28.camel@russell.cc> <30fb4e6b-0981-c53c-a1db-94138eaad268@c-s.fr> <20180926092806.GM23155@gate.crashing.org> <284752d1-6c32-bdca-72d3-4d8616b26fbf@c-s.fr>
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On Wed, Sep 26, 2018 at 11:41:26AM +0200, Christophe LEROY wrote:
> Le 26/09/2018 ? 11:28, Segher Boessenkool a ?crit?:
> >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