From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6897DCA9EC3 for ; Mon, 28 Oct 2019 15:12:54 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 34BE4222C5 for ; Mon, 28 Oct 2019 15:12:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="WJCCJ2oT" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 34BE4222C5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linaro.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:45604 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iP6hQ-0006ZT-Kl for qemu-devel@archiver.kernel.org; Mon, 28 Oct 2019 11:12:52 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44601) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iP6Uo-0007XA-QB for qemu-devel@nongnu.org; Mon, 28 Oct 2019 10:59:52 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iP6Um-00044l-Td for qemu-devel@nongnu.org; Mon, 28 Oct 2019 10:59:50 -0400 Received: from mail-wr1-x42d.google.com ([2a00:1450:4864:20::42d]:46253) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1iP6Uj-00043h-T9 for qemu-devel@nongnu.org; Mon, 28 Oct 2019 10:59:47 -0400 Received: by mail-wr1-x42d.google.com with SMTP id n15so10199980wrw.13 for ; Mon, 28 Oct 2019 07:59:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=xrU7w4s7KSKnwqBpSI+WZTUaBsgqmQLo3umhoYb3GT8=; b=WJCCJ2oTpp+tWKf6mXQ/dvcaQaxrUpqCWL4VFs3Jb22hfO9D9a5isRA4YPGMDZNLN9 fAL8fDy9gFonH/bW+UAvXJCeHfLOsO1va9R6wVno/Hh2dJqKj6/WpdKCXKG0D+13h+3S kJbc7o/l1E42XwNEIIrhTigTjjTBkA/g9irNBgU8R2S+cPjzOhFpGdsBOnmw6sNGDovK Wj0c/ZdPoRDwo1LnFxHLEGCQwU1QYxSO2zJb2f+pb8MZVwkrwDBpPL9A6D8aWyfc34p1 v1ONbRJCD3VAsXmlwLdXW79cPCm0NdTEr8p3ctxddNxCJGaxngpvL1uXZ1yVJLx5TZFz JRcg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=xrU7w4s7KSKnwqBpSI+WZTUaBsgqmQLo3umhoYb3GT8=; b=AZYFCDOMI9tKBlQOUfcbnF3lZWhIPwDY0IGVngnYC6d7d0wePJ62b3VJr2odku2/vF FuwGZJJtyRuwpz2l//wIP6eRjVghUjpFq7Z3KZlbQfxXqIwJJSBe2j4ecjaHFRVwqWMo 24P/vXPwIEIMsZUmjHj5UI5ycysOwPLi/hU2s7zYjYWmtfwn5mkGjRafO1CWWzdiVEVR Usd74WANziOxEZNqNSVUzAPOGkMk2MxkXP0dwWdQNe9F0homZBqMmMT79YLve6iSvPoF uFwLo+z9LtXIoY7y6gkAwFaPAypx9a/ip17QqBs4bxq+zImwD+D4bRknkCTm2028v921 jIjA== X-Gm-Message-State: APjAAAXUVp3mPxSap6sACs90oIwdMgWkvzuxYudEbl/JSfkJRy+VXUJO j3NbK9ZhO25LW/r5OIiFkHRmw0WS1vn0aA== X-Google-Smtp-Source: APXvYqyuLysnOgizh4jiAve6pX33fbanxvixoYNJUhWzr/RJgyIKLSaUYvPkCcQRkPzVvwiAVIN6Uw== X-Received: by 2002:a5d:4f91:: with SMTP id d17mr15714161wru.184.1572274784547; Mon, 28 Oct 2019 07:59:44 -0700 (PDT) Received: from localhost.localdomain (230.106.138.88.rev.sfr.net. [88.138.106.230]) by smtp.gmail.com with ESMTPSA id 143sm14842876wmb.33.2019.10.28.07.59.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Oct 2019 07:59:43 -0700 (PDT) From: Richard Henderson To: qemu-devel@nongnu.org Subject: [PULL v2 06/12] exec: Use const alias for TARGET_PAGE_BITS_VARY Date: Mon, 28 Oct 2019 15:59:31 +0100 Message-Id: <20191028145937.10914-7-richard.henderson@linaro.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20191028145937.10914-1-richard.henderson@linaro.org> References: <20191028145937.10914-1-richard.henderson@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2a00:1450:4864:20::42d X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: peter.maydell@linaro.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Using a variable that is declared "const" for this tells the compiler that it may read the value once and assume that it does not change across function calls. For target_page_size, this means we have only one assert per function, and one read of the variable. This reduces the size of qemu-system-aarch64 by 8k. Reviewed-by: Alex Bennée Reviewed-by: Paolo Bonzini Signed-off-by: Richard Henderson --- include/exec/cpu-all.h | 14 ++++++--- exec-vary.c | 66 +++++++++++++++++++++++++++++++++++++----- 2 files changed, 68 insertions(+), 12 deletions(-) diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h index 255bb186ac..0b449b98ba 100644 --- a/include/exec/cpu-all.h +++ b/include/exec/cpu-all.h @@ -210,10 +210,16 @@ static inline void stl_phys_notdirty(AddressSpace *as, hwaddr addr, uint32_t val /* page related stuff */ #ifdef TARGET_PAGE_BITS_VARY -extern bool target_page_bits_decided; -extern int target_page_bits; -#define TARGET_PAGE_BITS ({ assert(target_page_bits_decided); \ - target_page_bits; }) +typedef struct { + bool decided; + int bits; +} TargetPageBits; +#if defined(CONFIG_ATTRIBUTE_ALIAS) || !defined(IN_EXEC_VARY) +extern const TargetPageBits target_page; +#else +extern TargetPageBits target_page; +#endif +#define TARGET_PAGE_BITS ({ assert(target_page.decided); target_page.bits; }) #else #define TARGET_PAGE_BITS_MIN TARGET_PAGE_BITS #endif diff --git a/exec-vary.c b/exec-vary.c index 48c0ab306c..8725fd0285 100644 --- a/exec-vary.c +++ b/exec-vary.c @@ -19,11 +19,55 @@ #include "qemu/osdep.h" #include "qemu-common.h" + +#define IN_EXEC_VARY 1 + #include "exec/exec-all.h" #ifdef TARGET_PAGE_BITS_VARY -int target_page_bits; -bool target_page_bits_decided; +# ifdef CONFIG_ATTRIBUTE_ALIAS +/* + * We want to declare the "target_page" variable as const, which tells + * the compiler that it can cache any value that it reads across calls. + * This avoids multiple assertions and multiple reads within any one user. + * + * This works because we finish initializing the data before we ever read + * from the "target_page" symbol. + * + * This also requires that we have a non-constant symbol by which we can + * perform the actual initialization, and which forces the data to be + * allocated within writable memory. Thus "init_target_page", and we use + * that symbol exclusively in the two functions that initialize this value. + * + * The "target_page" symbol is created as an alias of "init_target_page". + */ +static TargetPageBits init_target_page; + +/* + * Note that this is *not* a redundant decl, this is the definition of + * the "target_page" symbol. The syntax for this definition requires + * the use of the extern keyword. This seems to be a GCC bug in + * either the syntax for the alias attribute or in -Wredundant-decls. + * + * See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91765 + */ +# pragma GCC diagnostic push +# pragma GCC diagnostic ignored "-Wredundant-decls" + +extern const TargetPageBits target_page + __attribute__((alias("init_target_page"))); + +# pragma GCC diagnostic pop +# else +/* + * When aliases are not supported then we force two different declarations, + * by way of suppressing the header declaration with IN_EXEC_VARY. + * We assume that on such an old compiler, LTO cannot be used, and so the + * compiler cannot not detect the mismatched declarations, and all is well. + */ +TargetPageBits target_page; +# define init_target_page target_page +# endif #endif bool set_preferred_target_page_bits(int bits) @@ -36,11 +80,11 @@ bool set_preferred_target_page_bits(int bits) */ #ifdef TARGET_PAGE_BITS_VARY assert(bits >= TARGET_PAGE_BITS_MIN); - if (target_page_bits == 0 || target_page_bits > bits) { - if (target_page_bits_decided) { + if (init_target_page.bits == 0 || init_target_page.bits > bits) { + if (init_target_page.decided) { return false; } - target_page_bits = bits; + init_target_page.bits = bits; } #endif return true; @@ -49,9 +93,15 @@ bool set_preferred_target_page_bits(int bits) void finalize_target_page_bits(void) { #ifdef TARGET_PAGE_BITS_VARY - if (target_page_bits == 0) { - target_page_bits = TARGET_PAGE_BITS_MIN; + if (init_target_page.bits == 0) { + init_target_page.bits = TARGET_PAGE_BITS_MIN; } - target_page_bits_decided = true; + init_target_page.decided = true; + + /* + * For the benefit of an -flto build, prevent the compiler from + * hoisting a read from target_page before we finish initializing. + */ + barrier(); #endif } -- 2.17.1