Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262888AbTIFHGH (ORCPT ); Sat, 6 Sep 2003 03:06:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263152AbTIFHGG (ORCPT ); Sat, 6 Sep 2003 03:06:06 -0400 Received: from nikam.ms.mff.cuni.cz ([195.113.18.106]:43975 "EHLO nikam.ms.mff.cuni.cz") by vger.kernel.org with ESMTP id S262888AbTIFHGC (ORCPT ); Sat, 6 Sep 2003 03:06:02 -0400 Date: Sat, 6 Sep 2003 09:06:01 +0200 From: Jan Hubicka To: Robert Love Cc: Andreas Jaeger , Linus Torvalds , Andi Kleen , akpm@osdl.org, rth@redhat.com, linux-kernel@vger.kernel.org, jh@suse.cz Subject: Re: [PATCH] Use -fno-unit-at-a-time if gcc supports it Message-ID: <20030906070601.GE9989@kam.mff.cuni.cz> References: <1062778587.8510.10.camel@boobies.awol.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1062778587.8510.10.camel@boobies.awol.org> User-Agent: Mutt/1.3.28i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3012 Lines: 78 > On Fri, 2003-09-05 at 11:17, Andreas Jaeger wrote: > > > > Since unit-at-a-time has better inlining heuristics the better way is > > to add the used attribute - but that takes some time. The short-term > > solution would be to add the compiler flag, > > Won't we get a linker error if a static symbol is used but > optimized-away? It shouldn't be hard to fix the n linker errors that > crop up. Yes, you get linker error. You may also run into misscompilation assuiming that function is static and it is both called by hand in asm and by function call and there is missing attribute used and asmlinkage definition. In that case GCC would conclude to change into register calling convention on i386 breaking asm code. I would expect this to be rare as functions tends to be used either by assembly or by normal code but not by both. > > And why are we using static symbols in inline assembly outside of the > compilation scope? The toplevel asm statements are common source of this at least in glibc. I didn't look much into the kernel sources. I would be very happy if someone did look on that. It may be well possible that implementing tricks you do currently with toplevel asm staements would need further extensions in GCC now and it would be nice to know about that. For instance it used to be possible to force function to go into given section by changing the section by hand, but now you have to use section attribute (that is cleaner anyway) > > Anyhow, if it generates an error, this isn't hard to fix. > > Here is the start... > > Robert Love > > > --- linux-rml/include/linux/compiler.h Fri Sep 5 11:57:56 2003 > +++ linux/include/linux/compiler.h Fri Sep 5 12:02:02 2003 > @@ -74,6 +74,19 @@ > #define __attribute_pure__ /* unimplemented */ > #endif > > +/* > + * As of gcc 3.2, we can mark a function as 'used' and gcc will assume that, > + * even if it does not find a reference to it in any compilation unit. We > + * need this for gcc 3.4 and beyond, which can optimize on a program-wide > + * scope, and not just one file at a time, to avoid static symbols being > + * discarded. > + */ > +#if (__GNUC__ == 3 && __GNUC_MINOR__ > 1) || __GNUC__ > 3 > +#define __attribute_used__ __attribute__((used)) > +#else > +#define __attribute_used__ /* unimplemented */ > +#endif > + I believe there is little trick - attribute used works either for variables or functions. Functions can be marked as used only for GCC 3.4+ if I am right, so you may need __attribute_used_function__ and __attribute_used_variable__ macros for that. Honza > /* This macro obfuscates arithmetic on a variable address so that gcc > shouldn't recognize the original var, and make assumptions about it */ > #define RELOC_HIDE(ptr, off) \ > > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/