From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received-SPF: Pass (sender SPF authorized) identity=mailfrom; client-ip=209.132.183.28; helo=mx1.redhat.com; envelope-from=lersek@redhat.com; receiver=edk2-devel@lists.01.org Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 8AD8D211D6810 for ; Thu, 7 Mar 2019 23:59:54 -0800 (PST) Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 52CCE3082128; Fri, 8 Mar 2019 07:59:54 +0000 (UTC) Received: from lacos-laptop-7.usersys.redhat.com (ovpn-120-151.rdu2.redhat.com [10.10.120.151]) by smtp.corp.redhat.com (Postfix) with ESMTP id AC8905D786; Fri, 8 Mar 2019 07:59:53 +0000 (UTC) To: Andrew Fish , edk2-devel References: <96DCE1C9-B02B-4520-A483-F72BBAAAB3B8@apple.com> From: Laszlo Ersek Message-ID: <480fe32f-032e-0bf8-a561-c41a16213b82@redhat.com> Date: Fri, 8 Mar 2019 08:59:52 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <96DCE1C9-B02B-4520-A483-F72BBAAAB3B8@apple.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Fri, 08 Mar 2019 07:59:54 +0000 (UTC) Subject: Re: UefiCpuPkg CpuDxe GDT init question? X-BeenThere: edk2-devel@lists.01.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: EDK II Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 08 Mar 2019 07:59:55 -0000 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Hi Andrew, On 03/07/19 23:37, Andrew Fish via edk2-devel wrote: > I'm trying to understand why gdtPtr.Base is casting to (UINT32)? > 1) gdtPtr.Base is a a UINTN > 2) It is legal for AllocateRuntimePool() to return an address > 4GB > > It seems like the code should just cast to (UINTN)? > > > https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/CpuDxe/CpuGdt.c#L151 I think you are right. I'm missing the background on this too. I tried to see if any justification was given in a git commit message, but according to "git blame", this code dates back to the original addition of the driver, namely commit a47463f28382 ("Add CPU DXE driver for IA32 & X64 processor architectures.", 2009-05-27). The commit message is unhelpful (for 3119 lines added). Thanks Laszlo > > > > VOID > InitGlobalDescriptorTable ( > VOID > ) > { > GDT_ENTRIES *gdt; > IA32_DESCRIPTOR gdtPtr; > > // > // Allocate Runtime Data for the GDT > // > gdt = AllocateRuntimePool (sizeof (GdtTemplate) + 8); > ASSERT (gdt != NULL); > gdt = ALIGN_POINTER (gdt, 8); > > // > // Initialize all GDT entries > // > CopyMem (gdt, &GdtTemplate, sizeof (GdtTemplate)); > > // > // Write GDT register > // > gdtPtr.Base = (UINT32)(UINTN)(VOID*) gdt; > gdtPtr.Limit = (UINT16) (sizeof (GdtTemplate) - 1); > AsmWriteGdtr (&gdtPtr); > > Thanks, > > Andrew Fish > _______________________________________________ > edk2-devel mailing list > edk2-devel@lists.01.org > https://lists.01.org/mailman/listinfo/edk2-devel >