From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-out.m-online.net (mail-out.m-online.net [212.18.0.10]) by ozlabs.org (Postfix) with ESMTP id 1ED49B7BF9 for ; Sun, 4 Oct 2009 00:51:32 +1000 (EST) From: Andreas Schwab To: Anton Blanchard Subject: Re: [patch 1/3] powerpc: Move 64bit VDSO to improve context switch performance References: <20090714065350.659537380@samba.org> <20090714065425.301516312@samba.org> Date: Sat, 03 Oct 2009 16:51:29 +0200 In-Reply-To: (Andreas Schwab's message of "Sat, 03 Oct 2009 16:15:38 +0200") Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linuxppc-dev@ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Andreas Schwab writes: > Andreas Schwab writes: > >> Anton Blanchard writes: >> >>> On 64bit applications the VDSO is the only thing in segment 0. Since the VDSO >>> is position independent we can remove the hint and let get_unmapped_area pick >>> an area. >> >> This breaks gdb. The section table in the VDSO image when mapped into >> the process no longer contains meaningful values, and gdb rejects it. > > The problem is that the load segment requires 64k alignment, but the > page allocater of course only provides PAGE_SIZE alignment, causing the > image to be unaligned in memory. Here is a patch. The disadvantage is that now gdb complains that the vdso does not contain section headers, because they are no longer covered by the load segment. Andreas. --- >>From 003c323c753d8717e58220c9560329882bcfa2c2 Mon Sep 17 00:00:00 2001 From: Andreas Schwab Date: Sat, 3 Oct 2009 16:46:45 +0200 Subject: [PATCH] powerpc: fix unaligned load segment in vdso64 Since the page allocator can only guarantee PAGE_SIZE alignment the load segment in the vdso object cannot claim more than that alignment. Use 4k alignment which is the minimum possible page size. Signed-off-by: Andreas Schwab --- arch/powerpc/kernel/vdso64/Makefile | 2 ++ 1 files changed, 2 insertions(+), 0 deletions(-) diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile index 79da65d..d4be303 100644 --- a/arch/powerpc/kernel/vdso64/Makefile +++ b/arch/powerpc/kernel/vdso64/Makefile @@ -10,7 +10,9 @@ obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64)) GCOV_PROFILE := n EXTRA_CFLAGS := -shared -fno-common -fno-builtin +# Force maximum page size of 4k so that it works with any page size EXTRA_CFLAGS += -nostdlib -Wl,-soname=linux-vdso64.so.1 \ + -Wl,-z,max-page-size=4096 \ $(call cc-ldoption, -Wl$(comma)--hash-style=sysv) EXTRA_AFLAGS := -D__VDSO64__ -s -- 1.6.4.4 -- Andreas Schwab, schwab@linux-m68k.org GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 "And now for something completely different."