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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Anthony PERARD <anthony.perard@citrix.com>
Cc: <devel@edk2.groups.io>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Jordan Justen <jordan.l.justen@intel.com>,
	Julien Grall <julien.grall@arm.com>,
	<xen-devel@lists.xenproject.org>,
	Laszlo Ersek <lersek@redhat.com>
Subject: Re: [Xen-devel] [PATCH v2 06/31] OvmfPkg/XenResetVector: Add new entry point for Xen PVH
Date: Mon, 15 Apr 2019 14:28:12 +0100	[thread overview]
Message-ID: <fb77cdf3-66a4-2c62-223e-58a4912e4fb3@citrix.com> (raw)
In-Reply-To: <20190415112547.GB1354@perard.uk.xensource.com>

On 15/04/2019 12:25, Anthony PERARD wrote:
> On Thu, Apr 11, 2019 at 01:52:27PM +0100, Andrew Cooper wrote:
>> On 09/04/2019 12:08, Anthony PERARD wrote:
>>> diff --git a/OvmfPkg/XenResetVector/Ia32/XenPVHMain.asm b/OvmfPkg/XenResetVector/Ia32/XenPVHMain.asm
>>> new file mode 100644
>>> index 0000000000..c4802bf4d1
>>> --- /dev/null
>>> +++ b/OvmfPkg/XenResetVector/Ia32/XenPVHMain.asm
>>> @@ -0,0 +1,47 @@
>>> +;------------------------------------------------------------------------------
>>> +; @file
>>> +; An entry point use by Xen when a guest is started in PVH mode.
>>> +;
>>> +; Copyright (c) 2019, Citrix Systems, Inc.
>>> +;
>>> +; This program and the accompanying materials are licensed and made available
>>> +; under the terms and conditions of the BSD License which accompanies this
>>> +; distribution.  The full text of the license may be found at
>>> +; http://opensource.org/licenses/bsd-license.php
>>> +;
>>> +; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
>>> +; WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
>>> +;
>>> +;------------------------------------------------------------------------------
>>> +
>>> +BITS    32
>>> +
>>> +xenPVHMain:
>>> +    mov     di, 'BP'
>>> +
>>> +    ; ESP -  Initial value of the EAX register (BIST: Built-in Self Test)
>>> +    mov     esp, eax
>> Where is the ABI described?  Xen has no BIST, so this will always have
>> the value 0. Stashing it in the stack pointer seems like a weird choice,
>> and a recipe for subtle bugs.
> I've just copied over what was done in the HVM case. I'll change that
> and ignore the value in `eax'.

The ASCII BP in %di is also bizarre without an explanation of where it
is intended to be used.

>>> +
>>> +    mov     eax, SEC_DEFAULT_CR0
>>> +    mov     cr0, eax
>>> +
>>> +    jmp     LINEAR_CODE_SEL:ADDR_OF(.jmpToNewCodeSeg)
>>> +.jmpToNewCodeSeg:
>>> +
>>> +    mov     eax, SEC_DEFAULT_CR4
>>> +    mov     cr4, eax
>>> +
>>> +    mov     ax, LINEAR_SEL
>>> +    mov     ds, ax
>>> +    mov     es, ax
>>> +    mov     fs, ax
>>> +    mov     gs, ax
>>> +    mov     ss, ax
>>> +
>>> +    ; return to the Main16
>>> +    OneTimeCallRet TransitionFromReal16To32BitFlat
>> Is there any description of what OneTimeCallRet is, and why a simple jmp
>> wont do?
> That's is used to return to where the `OneTimeCall' macro has been
> used. In this assembly, they don't use `call' and `ret', instead there
> is a set of two macros:
>
> %macro  OneTimeCall 1
>     jmp     %1
> %1 %+ OneTimerCallReturn:
> %endmacro
>
> %macro  OneTimeCallRet 1
>     jmp     %1 %+ OneTimerCallReturn
> %endmacro

I found these, but the complete lack of any documentation makes them
entirely opaque, especially as they are not actually call/ret instructions.

Even if they are suppose to be used in matching pairs, OneTimeCall
hasn't been used so far in the PVH code, so where is this going to
actually go to?

~Andrew

  reply	other threads:[~2019-04-15 13:28 UTC|newest]

Thread overview: 84+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-09 11:08 [PATCH v2 00/31] Specific platform to run OVMF in Xen PVH and HVM guests Anthony PERARD
2019-04-09 11:08 ` [PATCH v2 01/31] OvmfPkg/ResetSystemLib: Add missing dependency on PciLib Anthony PERARD
2019-04-10  8:48   ` [edk2-devel] " Laszlo Ersek
2019-04-10  9:16     ` Jordan Justen
2019-04-09 11:08 ` [PATCH v2 02/31] OvmfPkg: Create platform XenOvmf Anthony PERARD
2019-04-10  9:32   ` [edk2-devel] " Laszlo Ersek
2019-04-15 10:53     ` Anthony PERARD
2019-04-10  9:48   ` Jordan Justen
2019-04-10 14:27     ` Laszlo Ersek
2019-04-10 16:27       ` Ard Biesheuvel
2019-04-10 18:37       ` Jordan Justen
2019-04-11  7:34         ` Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 03/31] OvmfPkg: Introduce XenResetVector Anthony PERARD
2019-04-10  9:46   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 04/31] OvmfPkg: Introduce XenPlatformPei Anthony PERARD
2019-04-10 10:37   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 05/31] OvmfPkg/XenOvmf: Creating an ELF header Anthony PERARD
2019-04-11 10:43   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 06/31] OvmfPkg/XenResetVector: Add new entry point for Xen PVH Anthony PERARD
2019-04-11 10:49   ` [edk2-devel] " Laszlo Ersek
2019-04-11 12:52   ` [Xen-devel] " Andrew Cooper
2019-04-15 11:25     ` Anthony PERARD
2019-04-15 13:28       ` Andrew Cooper [this message]
2019-04-09 11:08 ` [PATCH v2 07/31] OvmfPkg/XenResetVector: Saving start of day pointer for PVH guests Anthony PERARD
2019-04-11 11:09   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 08/31] OvmfPkg/XenResetVector: Allow to jumpstart from either hvmloader or PVH Anthony PERARD
2019-04-11 11:19   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 09/31] OvmfPkg/XenOvmf: use a TimerLib instance that depends only on the CPU Anthony PERARD
2019-04-11 11:25   ` [edk2-devel] " Laszlo Ersek
2019-04-11 11:33     ` Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 10/31] OvmfPkg/XenPlatformPei: Detect OVMF_INFO from hvmloader Anthony PERARD
2019-04-11 11:47   ` [edk2-devel] " Laszlo Ersek
2019-04-11 11:47     ` Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 11/31] OvmfPkg/XenPlatformPei: Use mXenHvmloaderInfo to get E820 Anthony PERARD
2019-04-11 11:49   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 12/31] OvmfPkg/XenPlatformPei: Grab RSDP from PVH guest start of day struct Anthony PERARD
2019-04-11 11:58   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 13/31] OvmfPkg/Library/XenPlatformLib: New library Anthony PERARD
2019-04-11 12:10   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 14/31] OvmfPkg/AcpiPlatformDxe: Use PVH RSDP if exist Anthony PERARD
2019-04-11 12:20   ` [edk2-devel] " Laszlo Ersek
2019-04-11 12:23     ` Laszlo Ersek
2019-04-11 12:31       ` Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 15/31] OvmfPkg/XenHypercallLib: Enable it in PEIM Anthony PERARD
2019-04-12  9:07   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 16/31] OvmfPkg/XenPlatformPei: Introduce XenHvmloaderDetected Anthony PERARD
2019-04-12  9:08   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 17/31] OvmfPkg/XenPlatformPei: Reserve hvmloader's memory only when it as runned Anthony PERARD
2019-04-12  9:09   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 18/31] OvmfPkg/XenPlatformPei: Setup HyperPages earlier Anthony PERARD
2019-04-12  9:17   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 19/31] OvmfPkg/XenPlatformPei: Introduce XenPvhDetected Anthony PERARD
2019-04-12  9:20   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 20/31] OvmfPkg: Import XENMEM_memory_map hypercall to Xen/memory.h Anthony PERARD
2019-04-12  9:22   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 21/31] OvmfPkg/XenPlatformPei: Get E820 table via hypercall Anthony PERARD
2019-04-12  9:33   ` [edk2-devel] " Laszlo Ersek
2019-04-12  9:45     ` [Xen-devel] " Andrew Cooper
2019-04-09 11:08 ` [PATCH v2 22/31] OvmfPkg/XenPlatformPei: Rework memory detection Anthony PERARD
2019-04-12 11:15   ` [edk2-devel] " Laszlo Ersek
2019-04-15 13:42     ` Anthony PERARD
2019-04-09 11:08 ` [PATCH v2 23/31] OvmfPkg/XenPlatformPei: Reserve VGA memory region, to boot Linux Anthony PERARD
2019-04-15 13:21   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 24/31] OvmfPkg/XenPlatformPei: Ignore missing PCI Host Bridge on Xen PVH Anthony PERARD
2019-04-15 13:29   ` [edk2-devel] " Laszlo Ersek
2019-04-15 13:33     ` Laszlo Ersek
2019-04-15 13:37   ` [Xen-devel] " Andrew Cooper
2019-04-09 11:08 ` [PATCH v2 25/31] OvmfPkg/PlatformBootManagerLib: Handle the absence of PCI bus " Anthony PERARD
2019-04-15 13:33   ` [edk2-devel] " Laszlo Ersek
2019-04-15 13:49     ` Laszlo Ersek
2019-04-15 14:40       ` Anthony PERARD
2019-04-15 17:57         ` Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 26/31] OvmfPkg/XenOvmf: Override PcdFSBClock to Xen vLAPIC timer frequency Anthony PERARD
2019-04-15 13:52   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 27/31] OvmfPkg/XenOvmf: Introduce XenTimerDxe Anthony PERARD
2019-04-15 14:07   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 28/31] OvmfPkg/PlatformBootManagerLib: Use a Xen console for ConOut/ConIn Anthony PERARD
2019-04-15 14:56   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 29/31] OvmfPkg: Introduce XenIoPvhDxe to initialize Grant Tables Anthony PERARD
2019-04-16  8:49   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 30/31] OvmfPkg: Move XenRealTimeClockLib from ArmVirtPkg Anthony PERARD
2019-04-16  8:53   ` [edk2-devel] " Laszlo Ersek
2019-04-09 11:08 ` [PATCH v2 31/31] OvmfPkg/XenOvmf: use RealTimeClockRuntimeDxe from EmbeddedPkg Anthony PERARD
2019-04-16  8:58   ` [edk2-devel] " Laszlo Ersek

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