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[172.254.253.50]) by smtp.gmail.com with ESMTPSA id o1sm2456272qtb.82.2019.10.23.08.45.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Oct 2019 08:45:11 -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; bh=GvLqP4YBrj+nrlStAyuwbfcMGIRPPiTu+vJ+23TQgAw=; b=aEmAmX23InlnUT2icHg3aEvWcd49dzoz4tbuKp+wnSiTzBvcUrDLYrPrMHv9kwvBoR b9WlmgYjlZNXvCaej6FvgZSEcjkfVLvTg0I2djVAFWAo0wCkqt0x/I/MGRu5n0mKdczy EgPCoqsGfSzTt6VKsxkEkJndlPDk6k+3KNgacLCS2Ybu495vzIGN4JYK05cRLjoQZ76+ cNKnvW5Q21wIaLH1lFYI589K+Sx2g3Eq9EJ68KivWEP/s/pI9xrm6vTjbjMKjlnm7zjK G/5Nh2kpQH5y7DvVUzICh0Vt4VXFkQV0U2P63J1fm3dAzE8v/SkuOHN0HXK/YHErMhkM vuug== 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; bh=GvLqP4YBrj+nrlStAyuwbfcMGIRPPiTu+vJ+23TQgAw=; b=bsiBlAs5Cc30BerFvt6cBckN5g5tX5K61GIRRkUDZAxC4GCXk9wW+IsujyEOIkSvU/ WfNSplOqd1SHGK5u+AxAYZvyn43sPN+Vw+dY57VCxxThbSI2o9kWc0VnZ18wIIJXTrw+ E/y66wF4tO1NSfsL8SJmOF+BEW13bsdhgc1mc4tvsqZmm19j6QzdxUZU1XrCvu33UDiv nv0Va0ntohc8F2iNSq/YM2nJycx5iKmDCZ4cnGGJ2k8KHqzPVsDNQgQxLrYE2kJHLQlI cnPwvULRxcpHnKjinb77md85PFRnj6ST51M8V9toFHatcFT9fxORhu4RHD8vqVAl0UWT ltnw== X-Gm-Message-State: APjAAAVIWCbhcTswvbxCXC/zL6hqs4Xc4fnK+iXDbAuBqNXO1x5F/ROr lxmPEcM6XDWjaw7d+8MnzrksswKVnZk= X-Google-Smtp-Source: APXvYqzPMQXqII0RIFiLAvVcq6huIg3ZdYpjVAcAQydEIsP9Juw2FS79y0dcZR3YvaOHq2B9IG9zyA== X-Received: by 2002:aed:2687:: with SMTP id q7mr9746711qtd.382.1571845512179; Wed, 23 Oct 2019 08:45:12 -0700 (PDT) From: Richard Henderson To: qemu-devel@nongnu.org Subject: [PATCH v2 4/7] exec: Use const alias for TARGET_PAGE_BITS_VARY Date: Wed, 23 Oct 2019 11:45:02 -0400 Message-Id: <20191023154505.30521-5-richard.henderson@linaro.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20191023154505.30521-1-richard.henderson@linaro.org> References: <20191023154505.30521-1-richard.henderson@linaro.org> X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2607:f8b0:4864:20::843 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: pbonzini@redhat.com, alex.bennee@linaro.org Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: pass (identity @linaro.org) Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" 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: Paolo Bonzini Signed-off-by: Richard Henderson Reviewed-by: Alex Benn=C3=A9e --- v2: Notice CONFIG_ATTRIBUTE_ALIAS, and work around Xcode 9 lossage. --- include/exec/cpu-all.h | 14 +++++++--- exec-vary.c | 60 ++++++++++++++++++++++++++++++++++++------ 2 files changed, 62 insertions(+), 12 deletions(-) diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h index 255bb186ac..76515dc8d9 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 */ =20 #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..e0befd502a 100644 --- a/exec-vary.c +++ b/exec-vary.c @@ -19,11 +19,55 @@ =20 #include "qemu/osdep.h" #include "qemu-common.h" + +#define IN_EXEC_VARY 1 + #include "exec/exec-all.h" =20 #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 initialize the target_page data very early, in a + * location far removed from the functions that require the final results. + * + * 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=3D91765 + */ +# 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 =20 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 >=3D TARGET_PAGE_BITS_MIN); - if (target_page_bits =3D=3D 0 || target_page_bits > bits) { - if (target_page_bits_decided) { + if (init_target_page.bits =3D=3D 0 || init_target_page.bits > bits) { + if (init_target_page.decided) { return false; } - target_page_bits =3D bits; + init_target_page.bits =3D bits; } #endif return true; @@ -49,9 +93,9 @@ bool set_preferred_target_page_bits(int bits) void finalize_target_page_bits(void) { #ifdef TARGET_PAGE_BITS_VARY - if (target_page_bits =3D=3D 0) { - target_page_bits =3D TARGET_PAGE_BITS_MIN; + if (init_target_page.bits =3D=3D 0) { + init_target_page.bits =3D TARGET_PAGE_BITS_MIN; } - target_page_bits_decided =3D true; + init_target_page.decided =3D true; #endif } --=20 2.17.1