From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from integral2.. (unknown [182.2.70.248]) by gnuweeb.org (Postfix) with ESMTPSA id 9621F7EDA1; Tue, 1 Mar 2022 09:46:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gnuweeb.org; s=default; t=1646128005; bh=WBPkvI6aPFsjLmmXFdKcv2XaHR9dWe3/s/g6sbGKna4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DRpW3A0VFw2Sq92C1uOIr/E11mt1vg2SdIFiQFmGHPuY97NhfuYU/24Qk43MyGXYW FquRXuiD6x+aVARdJZSitV02GgthHfiyh/W1WcAjct15pTzw2sL+w3+ggcykXim1aO +RJU0olmEEVAGquOKgauUkLBVJ6c+Ui8gGiVog2GLffna6vKqOJ43AiT2QFLnVV6AT RUZklZCZPBeG31EKWWQaeykyvOT8/PB7qMhfkBFw8WOKQMuTIQozXX5pmw7Cb965cv i8o/HaQX/OeIoyz+SREw5nu1QMdSbTh7e7RB5c6d+X2qwOqUnnH3xyipSKrsthwthk CeqJf7S2rMH/A== From: Ammar Faizi To: Borislav Petkov Cc: Dave Hansen , "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , Tony Luck , linux-edac@vger.kernel.org, linux-kernel@vger.kernel.org, gwml@vger.gnuweeb.org, x86@kernel.org, stable@vger.kernel.org, Alviro Iskandar Setiawan , Jiri Hladky , Greg Kroah-Hartman , Ammar Faizi Subject: [PATCH v4 1/2] x86/delay: Fix the wrong asm constraint in `delay_loop()` Date: Tue, 1 Mar 2022 16:46:07 +0700 Message-Id: <20220301094608.118879-2-ammarfaizi2@gnuweeb.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20220301094608.118879-1-ammarfaizi2@gnuweeb.org> References: <20220301094608.118879-1-ammarfaizi2@gnuweeb.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit List-Id: From: Ammar Faizi The asm constraint does not reflect that the asm statement can modify the value of @loops. But the asm statement in delay_loop() does change the @loops. If by any chance the compiler inlines this function, it may clobber random stuff (e.g. local variable, important temporary value in reg, etc.). Fortunately, delay_loop() is only called indirectly (so it can't inline), and then the register it clobbers is %rax (which is by the nature of the calling convention, it's a caller saved register), so it didn't yield any bug. ^ That shouldn't be an excuse for using the wrong constraint anyway. This changes "a" (as an input) to "+a" (as an input and output). Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" Cc: Jiri Hladky Fixes: e01b70ef3eb3 ("x86: fix bug in arch/i386/lib/delay.c file, delay_loop function") Signed-off-by: Ammar Faizi --- Fortunately, the constraint violation that's fixed by patch 1 doesn't yield any bug due to the nature of System V ABI. Should we backport this? arch/x86/lib/delay.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c index 65d15df6212d..0e65d00e2339 100644 --- a/arch/x86/lib/delay.c +++ b/arch/x86/lib/delay.c @@ -54,8 +54,8 @@ static void delay_loop(u64 __loops) " jnz 2b \n" "3: dec %0 \n" - : /* we don't need output */ - :"a" (loops) + : "+a" (loops) + : ); } -- 2.32.0