From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759326AbbJIASr (ORCPT ); Thu, 8 Oct 2015 20:18:47 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:35329 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758938AbbJIARb (ORCPT ); Thu, 8 Oct 2015 20:17:31 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Russell King" , "Nicolas Pitre" , "Ard Biesheuvel" Date: Fri, 09 Oct 2015 01:12:28 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 066/107] ARM: 8429/1: disable GCC SRA optimization In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.247 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.72-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Ard Biesheuvel commit a077224fd35b2f7fbc93f14cf67074fc792fbac2 upstream. While working on the 32-bit ARM port of UEFI, I noticed a strange corruption in the kernel log. The following snprintf() statement (in drivers/firmware/efi/efi.c:efi_md_typeattr_format()) snprintf(pos, size, "|%3s|%2s|%2s|%2s|%3s|%2s|%2s|%2s|%2s]", was producing the following output in the log: | | | | | |WB|WT|WC|UC] | | | | | |WB|WT|WC|UC] | | | | | |WB|WT|WC|UC] |RUN| | | | |WB|WT|WC|UC]* |RUN| | | | |WB|WT|WC|UC]* | | | | | |WB|WT|WC|UC] |RUN| | | | |WB|WT|WC|UC]* | | | | | |WB|WT|WC|UC] |RUN| | | | | | | |UC] |RUN| | | | | | | |UC] As it turns out, this is caused by incorrect code being emitted for the string() function in lib/vsprintf.c. The following code if (!(spec.flags & LEFT)) { while (len < spec.field_width--) { if (buf < end) *buf = ' '; ++buf; } } for (i = 0; i < len; ++i) { if (buf < end) *buf = *s; ++buf; ++s; } while (len < spec.field_width--) { if (buf < end) *buf = ' '; ++buf; } when called with len == 0, triggers an issue in the GCC SRA optimization pass (Scalar Replacement of Aggregates), which handles promotion of signed struct members incorrectly. This is a known but as yet unresolved issue. (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65932). In this particular case, it is causing the second while loop to be executed erroneously a single time, causing the additional space characters to be printed. So disable the optimization by passing -fno-ipa-sra. Acked-by: Nicolas Pitre Signed-off-by: Ard Biesheuvel Signed-off-by: Russell King Signed-off-by: Ben Hutchings --- arch/arm/Makefile | 8 ++++++++ 1 file changed, 8 insertions(+) --- a/arch/arm/Makefile +++ b/arch/arm/Makefile @@ -53,6 +53,14 @@ endif comma = , +# +# The Scalar Replacement of Aggregates (SRA) optimization pass in GCC 4.9 and +# later may result in code being generated that handles signed short and signed +# char struct members incorrectly. So disable it. +# (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65932) +# +KBUILD_CFLAGS += $(call cc-option,-fno-ipa-sra) + # This selects which instruction set is used. # Note that GCC does not numerically define an architecture version # macro, but instead defines a whole series of macros which makes