From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40QKk1649GzF1vG for ; Tue, 17 Apr 2018 19:30:49 +1000 (AEST) Date: Tue, 17 Apr 2018 19:30:44 +1000 From: Paul Mackerras To: Christophe Leroy Cc: Benjamin Herrenschmidt , Michael Ellerman , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] powerpc/misc: get rid of add_reloc_offset() Message-ID: <20180417093044.GA9105@fergus.ozlabs.ibm.com> References: <20180417075624.962AB6C038@po15720vm.idsi0.si.c-s.fr> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20180417075624.962AB6C038@po15720vm.idsi0.si.c-s.fr> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Apr 17, 2018 at 09:56:24AM +0200, Christophe Leroy wrote: > add_reloc_offset() is almost redundant with reloc_offset() > > Signed-off-by: Christophe Leroy > --- > arch/powerpc/include/asm/setup.h | 3 +-- > arch/powerpc/kernel/misc.S | 16 ---------------- > arch/powerpc/kernel/prom_init_check.sh | 2 +- > 3 files changed, 2 insertions(+), 19 deletions(-) > > diff --git a/arch/powerpc/include/asm/setup.h b/arch/powerpc/include/asm/setup.h > index 27fa52ed6d00..115e0896ffa7 100644 > --- a/arch/powerpc/include/asm/setup.h > +++ b/arch/powerpc/include/asm/setup.h > @@ -17,10 +17,9 @@ extern void note_scsi_host(struct device_node *, void *); > > /* Used in very early kernel initialization. */ > extern unsigned long reloc_offset(void); > -extern unsigned long add_reloc_offset(unsigned long); > extern void reloc_got2(unsigned long); > > -#define PTRRELOC(x) ((typeof(x)) add_reloc_offset((unsigned long)(x))) > +#define PTRRELOC(x) ((typeof(x)) ((unsigned long)(x) + reloc_offset())) NAK. This is how it used to be, and we changed it in order to prevent gcc from making incorrect assumptions. If you use the form with the explicit addition, and x is the address of an array, gcc will assume that the result is within the bounds of the array (apparently the C standard says it can do that) and potentially generate incorrect code. I recall that we had an actual case where gcc was generating incorrect code, though I don't recall the details, as this was some time before 2002. Paul.