Re: [Xen-devel] [PATCH v3 21/27] Ovmf/Xen: add ARM and AArch64 support to XenBusDxe

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 3 Feb 2015, Ard Biesheuvel wrote:
> This patch adds support to XenBusDxe for executing on ARM and AArch64
> machines (the former only when built with GCC).

Wouldn't it be simpler to just provide an asm implementation of them?
Similarly to OvmfPkg/XenBusDxe/X64/TestAndClearBit.nasm and
OvmfPkg/XenBusDxe/X64/InterlockedCompareExchange16.nasm?

> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> ---
>  OvmfPkg/XenBusDxe/AtomicsGcc.c  | 44 
> +++++++++++++++++++++++++++++++++++++++++
>  OvmfPkg/XenBusDxe/XenBusDxe.inf |  3 +++
>  2 files changed, 47 insertions(+)
>  create mode 100644 OvmfPkg/XenBusDxe/AtomicsGcc.c
> 
> diff --git a/OvmfPkg/XenBusDxe/AtomicsGcc.c b/OvmfPkg/XenBusDxe/AtomicsGcc.c
> new file mode 100644
> index 000000000000..a0bdcbf67440
> --- /dev/null
> +++ b/OvmfPkg/XenBusDxe/AtomicsGcc.c
> @@ -0,0 +1,44 @@
> +/** @file
> +  Arch-independent implementations of XenBusDxe atomics using GCC __builtins
> +
> +  Copyright (C) 2014, Linaro Ltd.
> +
> +  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.
> +
> +**/
> +
> +UINT16
> +EFIAPI
> +InternalSyncCompareExchange16 (
> +  IN      volatile UINT16           *Value,
> +  IN      UINT16                    CompareValue,
> +  IN      UINT16                    ExchangeValue
> +  )
> +{
> +  return __sync_val_compare_and_swap_2 (Value, CompareValue, ExchangeValue);
> +}
> +
> +INT32
> +EFIAPI
> +TestAndClearBit (
> +  IN INT32            Bit,
> +  IN volatile VOID    *Address
> +  )
> +{
> +  //
> +  // Calculate the effective address relative to 'Address' based on the
> +  // higher order bits of 'Bit'. Use signed shift instead of division to
> +  // ensure we round towards -Inf, and end up with a positive shift in 'Bit',
> +  // even if 'Bit' itself is negative.
> +  //
> +  Address += (Bit >> 5) * sizeof(INT32);
> +  Bit &= 31;
> +
> +  return (__sync_fetch_and_and_4 (Address, ~(1U << Bit)) & (1U << Bit)) != 0;
> +}
> diff --git a/OvmfPkg/XenBusDxe/XenBusDxe.inf b/OvmfPkg/XenBusDxe/XenBusDxe.inf
> index 31553ac5a64a..949ec0a0c732 100644
> --- a/OvmfPkg/XenBusDxe/XenBusDxe.inf
> +++ b/OvmfPkg/XenBusDxe/XenBusDxe.inf
> @@ -54,6 +54,9 @@
>    X64/InterlockedCompareExchange16.nasm
>    X64/TestAndClearBit.nasm
>  
> +[Sources.AARCH64, Sources.ARM]
> +  AtomicsGcc.c | GCC
> +
>  [LibraryClasses]
>    UefiDriverEntryPoint
>    UefiBootServicesTableLib
> -- 
> 1.8.3.2
> 

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