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=-3.8 required=3.0 tests=BAYES_00,DKIM_ADSP_CUSTOM_MED, DKIM_INVALID,DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 828B8C433EA for ; Thu, 16 Jul 2020 13:25:55 +0000 (UTC) Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) (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 3BCF720760 for ; Thu, 16 Jul 2020 13:25:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="DKaVS027" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3BCF720760 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernelnewbies-bounces@kernelnewbies.org Received: from localhost ([::1] helo=shelob.surriel.com) by shelob.surriel.com with esmtp (Exim 4.94) (envelope-from ) id 1jw3sy-00018g-3B; Thu, 16 Jul 2020 09:25:16 -0400 Received: from mail-qk1-x72d.google.com ([2607:f8b0:4864:20::72d]) by shelob.surriel.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1jw3sv-00018a-2D for Kernelnewbies@kernelnewbies.org; Thu, 16 Jul 2020 09:25:13 -0400 Received: by mail-qk1-x72d.google.com with SMTP id 145so5431457qke.9 for ; Thu, 16 Jul 2020 06:25:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=SdcmW9cSX/XpwQePZiDk3TPmTX878m3IEGUe4AnwksQ=; b=DKaVS027ux2PQqUQIbB/8B4g4RWXtCbgBbeT5JrJLnMs1nim2ebDPwlSKG2VCuAxT+ xNGHD1dOzpseprv+FoHMYMDSSHSuA3YXDqYYda0wDNp4vd/0xUEucfFNIUo8/EQ3yC1b yQrNQSlOtjzdAL2BZzEJ8SMVjNbUuHjC9aENBcmtK46/Ukcn1zl62X27WfN4F0JoX5YD ThS9eFk12b4Cnv5GO2j/s9nkZsYYctlqhCE9vkaCBpR5DGUdXwLqJsJr4aH/r3LbUZpk r9ZTAwn19F1ZcW7ttW6VAbddD0zIj8aBnqUl7ewtA94AMcXGvoKnL/BNcQ/l/6GZmSLg gJxA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=SdcmW9cSX/XpwQePZiDk3TPmTX878m3IEGUe4AnwksQ=; b=PjSEvLUwDB736t9NHtJ0B8AsIQG5ebF2eQ0tLN/ehkkD/QLbqZIfJIfQBaUofh8D0Y OARzzlioGe6MmLf9ylSbGGIOjWtm6WqQ75LbpapTwFHmF+S5rtK/SbR1fXxYKi/YKnAS SpiIWxxvIRAxT2bBGuseRET5iYJUt1Xkgu7GiPYYsRpPhb26i4WizH7mltNEoi5P2YR/ sUGxmqEZRRqtLCbqSxH9ILAjVZkRKqtgxP1zYi0vVW09tml26fRvGy6MzdV0d4vnnTWy c27aTiQrpSPdho6/mw8zRASpsqUJVuMLHiZc+PUIZYGc/czJfdUlZOODDasrR+dmarY/ YG4w== X-Gm-Message-State: AOAM533t9FDLbNvUI0mnS5eMFZoMBrOzlT/vdzqdcerO7rf1JSZYR/WZ 2d42UpfvwD8JZ9R+qXF328h+KobsfsDbNY7g7OQ= X-Google-Smtp-Source: ABdhPJxiX08l2pBFS2w3mFrEJZ/GIAYiHCkDF79n4cYkqXKPDMnTkuiWRySizGIVxBQqngmsrilKY1lAb4XvgH6qGw4= X-Received: by 2002:a37:6382:: with SMTP id x124mr3522703qkb.13.1594905910403; Thu, 16 Jul 2020 06:25:10 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: =?UTF-8?B?5a2Z5LiW6b6ZIHN1bnNoaWxvbmc=?= Date: Thu, 16 Jul 2020 21:24:59 +0800 Message-ID: Subject: Re: How to comprehend this code snippet: __asm__ __volatile__("rdtsc" : "=A"(t))? To: noloader@gmail.com Cc: kernelnewbies X-BeenThere: kernelnewbies@kernelnewbies.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Learn about the Linux kernel List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Errors-To: kernelnewbies-bounces@kernelnewbies.org SGksIEplZmYKClRoYW5rIHlvdSBmb3IgdGFraW5nIHRoZSB0aW1lIHRvIHJlc3BvbmQgdG8gbXkg cXVlc3Rpb24uClRoYW5rcyB0byB5b3VyIGhlbHAsIEkgaGF2ZSBhIGRlZXBlciB1bmRlcnN0YW5k aW5nIG9mIHRoaXMgbWF0dGVyLgoKPkFsc28gcmVhZCB0aGUgbm90ZSBpbiB0aGUgTWFjaGluZSBD b25zdHJhaW50cyBmb3I6Cj4gICB1bnNpZ25lZCBsb25nIGxvbmcgcmR0c2MgKHZvaWQpCj4gICAg ewo+ICAgICAgdW5zaWduZWQgbG9uZyBsb25nIHRpY2s7Cj4gICAgIF9fYXNtX18gX192b2xhdGls ZV9fKCJyZHRzYyI6Ij1BIih0aWNrKSk7Cj4gICAgICByZXR1cm4gdGljazsKPiAgICB9Cj5UaGUg bWFudWFsIHNheXMgdGhlIHBhdHRlcm4gaXMgd3JvbmcgZm9yIHg4Nl82NC4KVGhhbmsgeW91IGZv ciB5b3VyIG5vdGlmaWNhdGlvbi4gSSBjaGVjayBpdCBhbmQgZmluZCBpdCdzIGZvciBYODZfMzIu CkkgZGlkbid0IG5vdGljZSBzdWNoIGRpZmZlcmVuY2VzIGJlZm9yZS4KSGVyZSBpcyB0aGUgZnVs bCByZWxhdGVkIGNvZGUgc25pcHBldDoKCiNpZmRlZiBDT05GSUdfWDg2XzMyCiNkZWZpbmUgaXBp cGVfcmVhZF90c2ModCkgICAgICAgICAgICAgIFwKICAgX19hc21fXyBfX3ZvbGF0aWxlX18oInJk dHNjIiA6ICI9QSIodCkpCiNlbHNlICAvKiBYODZfNjQgKi8KI2RlZmluZSBpcGlwZV9yZWFkX3Rz Yyh0KSAgZG8geyAgICAgICAgXAogICB1bnNpZ25lZCBpbnQgX19hLF9fZDsgICAgICAgICAgIFwK ICAgYXNtIHZvbGF0aWxlKCJyZHRzYyIgOiAiPWEiIChfX2EpLCAiPWQiIChfX2QpKTsgXAogICAo dCkgPSAoKHVuc2lnbmVkIGxvbmcpX19hKSB8ICgoKHVuc2lnbmVkIGxvbmcpX19kKTw8MzIpOyBc Cn0gd2hpbGUoMCkKI2VuZGlmCgo+VGhlICdBJyBpcyB0aGUgY29uc3RyYWludCBFQVg6UkRYIHJl Z2lzdGVyIHBhaXIuCj5BbHNvIHNlZSBodHRwczovL2djYy5nbnUub3JnL29ubGluZWRvY3MvZ2Nj L01hY2hpbmUtQ29uc3RyYWludHMuaHRtbAo+YW5kIGh0dHBzOi8vZ2NjLmdudS5vcmcvb25saW5l ZG9jcy9nY2MvRXh0ZW5kZWQtQXNtLmh0bWwuClRoYW5rcyB0byB5b3VyIGF0dGFjaGVkIGRvY3Vt ZW50LCBJIGZpbmQgYSBsb3Qgb2YgdXNlZnVsIGluZm9ybWF0aW9uLgpCVFcsICBXaGF0IGRvZXMg IlRoZSBBIHJlZ2lzdGVyIiwgIlRoZSBCIHJlZ2lzdGVyIiBhbmQgZXRjIG1lYW4/CkkgZ29vZ2xl ZCBidXQgZGlkbid0IGdldCBhbnkgdXNlZnVsIGluZm9ybWF0aW9uLgpDb3VsZCB5b3UgcGxlYXNl IGdpdmUgbWUgYSBmZXcgYnJpZWYgZXhwbGFuYXRpb25zIG9yIHN1Z2dlc3Qgc29tZQpkb2N1bWVu dHMgZm9yIG1lIHRvIGdvIHRocm91Z2g/CgpUaGFuayB5b3UgZm9yIHlvdXIgYXR0ZW50aW9uIHRv IHRoaXMgbWF0dGVyLgpMb29raW5nIGZvcndhcmQgdG8gaGVhcmluZyBmcm9tIHlvdS4KQmVzdCBX aXNoZXMuCnN1bnNoaWxvbmcKCk9uIFRodSwgSnVsIDE2LCAyMDIwIGF0IDg6NTIgUE0gSmVmZnJl eSBXYWx0b24gPG5vbG9hZGVyQGdtYWlsLmNvbT4gd3JvdGU6Cj4KPiBPbiBUaHUsIEp1bCAxNiwg MjAyMCBhdCA4OjIyIEFNIOWtmeS4lum+mSBzdW5zaGlsb25nIDxzdW5zaGlsb25nMzY5QGdtYWls LmNvbT4gd3JvdGU6Cj4gPgo+ID4gSGVyZSBpcyB0aGUgY29kZSBzbmlwcGV0Ogo+ID4gI2RlZmlu ZSBpcGlwZV9yZWFkX3RzYyh0KSAgICAgICAgICAgICAgXAo+ID4gX19hc21fXyBfX3ZvbGF0aWxl X18oInJkdHNjIiA6ICI9QSIodCkpCj4KPiBJIGhvcGUgdGhhdCBpcyBpMzg2IG9ubHksIGFuZCBu b3QgeDg2XzY0Lgo+Cj4gPiBJIGZvdW5kIHRoYXQgdGhlIHJkdHNjIChSZWFkIFRpbWUtU3RhbXAg Q291bnRlcikgaW5zdHJ1Y3Rpb24gaXMgdXNlZAo+ID4gdG8gZGV0ZXJtaW5lIGhvdyBtYW55IENQ VSB0aWNrcyB0b29rIHBsYWNlIHNpbmNlIHRoZSBwcm9jZXNzb3Igd2FzCj4gPiByZXNldC4KPiA+ Cj4gPiBCdXQgd2hhdCBkb2VzCj4gPiAiPUEiKHQpCj4gPiBtZWFuPwo+Cj4gVGhlICc9QScgaXMg YSBHQ0MgbWFjaGluZSBjb25zdHJhaW50IGZvciBpMzg2IGFuZCBhbiBvdXRwdXQgb3BlcmFuZC4K PiBUaGUgJ0EnIGlzIHRoZSBjb25zdHJhaW50IEVBWDpSRFggcmVnaXN0ZXIgcGFpci4gVGhlICc9 JyBtZWFucyBpdCBpcwo+IGJlaW5nIHdyaXR0ZW4gdG8uCj4KPiBBbHNvIHNlZSBodHRwczovL2dj Yy5nbnUub3JnL29ubGluZWRvY3MvZ2NjL01hY2hpbmUtQ29uc3RyYWludHMuaHRtbAo+IGFuZCBo dHRwczovL2djYy5nbnUub3JnL29ubGluZWRvY3MvZ2NjL0V4dGVuZGVkLUFzbS5odG1sLgo+Cj4g QWxzbyByZWFkIHRoZSBub3RlIGluIHRoZSBNYWNoaW5lIENvbnN0cmFpbnRzIGZvcjoKPgo+ICAg ICB1bnNpZ25lZCBsb25nIGxvbmcgcmR0c2MgKHZvaWQpCj4gICAgIHsKPiAgICAgICB1bnNpZ25l ZCBsb25nIGxvbmcgdGljazsKPiAgICAgICBfX2FzbV9fIF9fdm9sYXRpbGVfXygicmR0c2MiOiI9 QSIodGljaykpOwo+ICAgICAgIHJldHVybiB0aWNrOwo+ICAgICB9Cj4KPiBUaGUgbWFudWFsIHNh eXMgdGhlIHBhdHRlcm4gaXMgd3JvbmcgZm9yIHg4Nl82NC4KPgo+IEplZmYKCl9fX19fX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCktlcm5lbG5ld2JpZXMgbWFpbGlu ZyBsaXN0Cktlcm5lbG5ld2JpZXNAa2VybmVsbmV3Ymllcy5vcmcKaHR0cHM6Ly9saXN0cy5rZXJu ZWxuZXdiaWVzLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2tlcm5lbG5ld2JpZXMK