From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-x232.google.com (mail-qk0-x232.google.com [IPv6:2607:f8b0:400d:c09::232]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 6AB5681997 for ; Thu, 5 Jan 2017 03:59:42 -0800 (PST) Received: by mail-qk0-x232.google.com with SMTP id n21so430283475qka.3 for ; Thu, 05 Jan 2017 03:59:42 -0800 (PST) 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; bh=iwugvyMP9raJyrBsV7oxBo8CQ7H8wLZCQlngsqWPuO8=; b=rpXrcnXNRqtc4F7kz4/f5Lpf0P+f/ISQYqkrSBvAROg7kK6CaEeQ8B4hXf/47rzTfk W9cdwk3EEPytxiT2zMTszMDhOiD9/JxQLa+z4XtHeaXT+FYNsnaaCPOrjgpKP1aIJoG4 Gwiqbnoz0KdOUA8EIZYu3HXbFTmn2r3BtONAPcDwyopG+9afqy/3RTZvMKmVl+bw97cn a7DpSE8jL4xZXlTKbyllJakn0dmJDisHPjeeKYvQjeon8/+4dpiSVmgv4p3zyNZ1tAsR VVcxy6KXEqsqpKdkAjOI5sWLoq4m7Kbh7NaY6SUkcyGtYxL4v0W6nC3rozJh912okP3S n7VQ== 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; bh=iwugvyMP9raJyrBsV7oxBo8CQ7H8wLZCQlngsqWPuO8=; b=lsDwFwHFi+lAY1sbHf4zRhi38I516gVQWncV4BRv+H23KFfCS6tjdiQSG+nncWsYcY JZzyzYrlssGvGS9XTowfuvBDNwq0IEk73CESGjgSF+W2eh0nJTOXm4XDxZGMwmevc+2P z2dh9zLYt1QwH4uNL23pg7NtZ0fWhQoFemz8V5xofPYsvM6F+iwPjwarPZG6w/bw8Nmb q+6F4/+3UeOY8PI7X2HSqpPMB1RlKCoGFh4gpKZFLqGtsl2yAOakIVDZt5dkpU/KrQ8W bay9JZzEwaoMwYBtT+3qrnjJ3M2gUWVSuSmcdpWjS0yYfPUR52cLh3TGuNJJLYwJKEzo K16w== X-Gm-Message-State: AIkVDXIfGYKQgapFRjbfVZ5nYbR3i6BP2APRJjfCegjKDHE12c1PE9+7lld5on/ao5xC/jk0cxpu1g1ZyVx1Kw== X-Received: by 10.55.11.130 with SMTP id 124mr69703570qkl.112.1483617581289; Thu, 05 Jan 2017 03:59:41 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Rafael Machado Date: Thu, 05 Jan 2017 11:59:30 +0000 Message-ID: To: "edk2-devel@lists.01.org" X-Content-Filtered-By: Mailman/MimeDel 2.1.21 Subject: Question about OS initialization at UEFI firmware (x86) X-BeenThere: edk2-devel@lists.01.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: EDK II Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 05 Jan 2017 11:59:42 -0000 Content-Type: text/plain; charset=UTF-8 Hi everyone I was taking a look at how the OS boots after the firmware and bootloader are done. To understand this I started to take a look at the linux source code, and the strange is that I saw some bios legacy interrupts being called. The flow I checked is this: void main(void) --> linux/arch/x86/boot/main.c int detect_memory(void) --> linux/arch/x86/boot/memory.c static int detect_memory_e820(void) --> linux/arch/x86/boot/memory.c intcall(0x15, &ireg, &oreg) --> linux/arch/x86/boot/memory.c At the last call the value of ireg is this one: ireg.ax = 0xe820; ireg.cx = sizeof buf; ireg.edx = SMAP; ireg.di = (size_t)&buf; As we can see this is done so the OS knows the memory map, so the OS can do all its magic. Finally, my question is: How could linux, or any other OS, boot on a system with UEFI firmware that does not have CSM (compatibility support module) ? I consider that some parts of the hypothetical OS need to be written to call some UEFI protocols. Am I right ? Thanks and Regards Rafael R. Machado