Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754595Ab3GOIrn (ORCPT ); Mon, 15 Jul 2013 04:47:43 -0400 Received: from gate.crashing.org ([63.228.1.57]:47566 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754103Ab3GOIrl (ORCPT ); Mon, 15 Jul 2013 04:47:41 -0400 Message-ID: <1373878026.19894.335.camel@pasglop> Subject: Re: [PATCH] module: ppc64 module CRC relocation fix causes perf issues From: Benjamin Herrenschmidt To: Scott Wood Cc: Paul Mackerras , Rusty Russell , Neil Horman , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Anton Blanchard Date: Mon, 15 Jul 2013 18:47:06 +1000 In-Reply-To: <20130715140450.573aab15@kryten> References: <20130715140450.573aab15@kryten> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.6.4-0ubuntu1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2810 Lines: 82 On Mon, 2013-07-15 at 14:04 +1000, Anton Blanchard wrote: > Module CRCs are implemented as absolute symbols that get resolved by > a linker script. We build an intermediate .o that contains an > unresolved symbol for each CRC. genksysms parses this .o, calculates > the CRCs and writes a linker script that "resolves" the symbols to > the calc Scott, can somebody from FSL test that on 32-bit and Ack it ? Thanks ! Cheers, Ben. > Unfortunately the ppc64 relocatable kernel sees these CRCs as symbols > that need relocating and relocates them at boot. Commit d4703aef > (module: handle ppc64 relocating kcrctabs when CONFIG_RELOCATABLE=y) > added a hook to reverse the bogus relocations. Part of this patch > created a symbol at 0x0: > > # head -2 /proc/kallsyms > 0000000000000000 T reloc_start > c000000000000000 T .__start > > This reloc_start symbol is causing lots of confusion to perf. It > thinks reloc_start is a massive function that stretches from 0x0 to > 0xc000000000000000 and we get various cryptic errors out of perf, > including: > > problem incrementing symbol count, skipping event > > This patch removes the reloc_start linker script label and instead > defines it as PHYSICAL_START. We also need to wrap it with > CONFIG_PPC64 because the ppc32 kernel can set a non zero > PHYSICAL_START at compile time and we wouldn't want to subtract > it from the CRCs in that case. > > Signed-off-by: Anton Blanchard > Cc: > --- > > This bug was originally reported on Fedora 19 (3.9.x), so I've marked > it for stable. > > Index: b/arch/powerpc/include/asm/module.h > =================================================================== > --- a/arch/powerpc/include/asm/module.h > +++ b/arch/powerpc/include/asm/module.h > @@ -82,10 +82,9 @@ struct exception_table_entry; > void sort_ex_table(struct exception_table_entry *start, > struct exception_table_entry *finish); > > -#ifdef CONFIG_MODVERSIONS > +#if defined(CONFIG_MODVERSIONS) && defined(CONFIG_PPC64) > #define ARCH_RELOCATES_KCRCTAB > - > -extern const unsigned long reloc_start[]; > +#define reloc_start PHYSICAL_START > #endif > #endif /* __KERNEL__ */ > #endif /* _ASM_POWERPC_MODULE_H */ > Index: b/arch/powerpc/kernel/vmlinux.lds.S > =================================================================== > --- a/arch/powerpc/kernel/vmlinux.lds.S > +++ b/arch/powerpc/kernel/vmlinux.lds.S > @@ -38,9 +38,6 @@ jiffies = jiffies_64 + 4; > #endif > SECTIONS > { > - . = 0; > - reloc_start = .; > - > . = KERNELBASE; > > /* -- 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/