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 535417EDA1; Tue, 1 Mar 2022 07:24:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gnuweeb.org; s=default; t=1646119470; bh=8R4MhWSJNcQ8evBE1421lIDo5eU1fFu91hoE2oHOvBg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Z3g2WQEcf34Z4PvcRAyjRxEpRuC4htiN+BSyqakNJ+1Y3378WoDhWpt+NiZOUqUoC 3FokngdHWA9UB/LEPTesdajRHH0Jsxkq1ktnpkcmQk37v8UEtgidF0WoprKgOpqcDk 1TTi+f6SI1u1IgLhjIK/WUEy7Yqyv/hBPCahaqMgCd52fqyNqCm1jFmeC/O+lmNVxX ATze2e4h6ikISAOia7ofnjLoLkPGE/zKKe+ePU99MAzUEv0mWp8WAYzdEnteiR2aMs bVQ7BlgXjZ1RxAL0CiIHW8ngkyjHTDWdhK5VcpoUyalLuIpjC2bO9Cs4DiAiGJVey3 M5kSFm+zRcb1A== 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, Ammar Faizi Subject: [PATCH 1/2] x86/delay: Fix the wrong asm constraint in `delay_loop()` Date: Tue, 1 Mar 2022 14:23:52 +0700 Message-Id: <20220301072353.95749-2-ammarfaizi2@gnuweeb.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20220301072353.95749-1-ammarfaizi2@gnuweeb.org> References: <20220301072353.95749-1-ammarfaizi2@gnuweeb.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit List-Id: 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" Fixes: e01b70ef3eb3080fecc35e15f68cd274c0a48163 ("x86: fix bug in arch/i386/lib/delay.c file, delay_loop function") Signed-off-by: Ammar Faizi --- 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