From patchwork Thu Jan 30 16:08:39 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christophe Leroy X-Patchwork-Id: 11358247 X-Patchwork-Delegate: paulburton@kernel.org Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 5F09913A4 for ; Thu, 30 Jan 2020 16:08:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3CE1D2083E for ; Thu, 30 Jan 2020 16:08:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=c-s.fr header.i=@c-s.fr header.b="k1nV5HNo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727328AbgA3QIm (ORCPT ); Thu, 30 Jan 2020 11:08:42 -0500 Received: from pegase1.c-s.fr ([93.17.236.30]:42999 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727374AbgA3QIm (ORCPT ); Thu, 30 Jan 2020 11:08:42 -0500 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 487ldf4nKzz9v6KS; Thu, 30 Jan 2020 17:08:38 +0100 (CET) Authentication-Results: localhost; dkim=pass reason="1024-bit key; insecure key" header.d=c-s.fr header.i=@c-s.fr header.b=k1nV5HNo; dkim-adsp=pass; dkim-atps=neutral X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id zEchKtxoY4H7; Thu, 30 Jan 2020 17:08:38 +0100 (CET) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 487ldf3KlDz9v6KL; Thu, 30 Jan 2020 17:08:38 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=c-s.fr; s=mail; t=1580400518; bh=4Kvsye4EMnIWruMrubU2uEdzOim6m1UTTTl/5OsNwDs=; h=In-Reply-To:References:From:Subject:To:Cc:Date:From; b=k1nV5HNo6Z2IrIBX+SaaIKQiwfqmxiGqGobyiJMGtGs/qsVlUVN6uqGFGqCXCQBBX oYi0dvc9bnGnv2gGUmnZDs/rlVHOXIphaNA3L790NbL4gYT4lQFP/lWLd3BOJcHwdr Z34gMu3hoEcwW/wmPHOdvX3sxhvVNl4WXKQxEebM= Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id DFEE78B87B; Thu, 30 Jan 2020 17:08:39 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id OdXw842o2kSJ; Thu, 30 Jan 2020 17:08:39 +0100 (CET) Received: from po14934vm.idsi0.si.c-s.fr (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 8723C8B877; Thu, 30 Jan 2020 17:08:39 +0100 (CET) Received: by po14934vm.idsi0.si.c-s.fr (Postfix, from userid 0) id 53A6765283; Thu, 30 Jan 2020 16:08:39 +0000 (UTC) Message-Id: In-Reply-To: References: From: Christophe Leroy Subject: [PATCH v5 5/6] lib/vdso: Allow architectures to override the ns shift operation To: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , nathanl@linux.ibm.com, arnd@arndb.de, tglx@linutronix.de, vincenzo.frascino@arm.com, luto@kernel.org Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, x86@kernel.org Date: Thu, 30 Jan 2020 16:08:39 +0000 (UTC) Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On powerpc/32, GCC (8.1) generates pretty bad code for the ns >>= vd->shift operation taking into account that the shift is always <= 32 and the upper part of the result is likely to be nul. GCC makes reversed assumptions considering the shift to be likely >= 32 and the upper part to be like not nul. unsigned long long shift(unsigned long long x, unsigned char s) { return x >> s; } results in: 00000018 : 18: 35 25 ff e0 addic. r9,r5,-32 1c: 41 80 00 10 blt 2c 20: 7c 64 4c 30 srw r4,r3,r9 24: 38 60 00 00 li r3,0 28: 4e 80 00 20 blr 2c: 54 69 08 3c rlwinm r9,r3,1,0,30 30: 21 45 00 1f subfic r10,r5,31 34: 7c 84 2c 30 srw r4,r4,r5 38: 7d 29 50 30 slw r9,r9,r10 3c: 7c 63 2c 30 srw r3,r3,r5 40: 7d 24 23 78 or r4,r9,r4 44: 4e 80 00 20 blr Even when forcing the shift with an &= 31, it still considers the shift as likely >= 32. Define a vdso_shift_ns() macro that can be overriden by architectures. Signed-off-by: Christophe Leroy --- lib/vdso/gettimeofday.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c index 0b4b71880f22..a5ee53d1ecee 100644 --- a/lib/vdso/gettimeofday.c +++ b/lib/vdso/gettimeofday.c @@ -38,6 +38,13 @@ u64 vdso_calc_delta(u64 cycles, u64 last, u64 mask, u32 mult) } #endif +#ifndef vdso_shift_ns +static __always_inline u64 vdso_shift_ns(u64 ns, unsigned long shift) +{ + return ns >> shift; +} +#endif + #ifdef CONFIG_TIME_NS static int do_hres_timens(const struct vdso_data *vdns, clockid_t clk, struct __kernel_timespec *ts) @@ -134,7 +141,7 @@ static __always_inline int do_hres(const struct vdso_data *vd, clockid_t clk, #endif ns += vdso_calc_delta(cycles, last, vd->mask, vd->mult); - ns >>= vd->shift; + ns = vdso_shift_ns(ns, vd->shift); sec = vdso_ts->sec; } while (unlikely(vdso_read_retry(vd, seq)));