Re: [edk2-devel] [edk2-test PATCH v1 2/2] SctPkg: Enable RISCV64 support using AARCH64 sources

["Leif Lindholm" <leif@nuviainc.com>]

On Mon, Feb 08, 2021 at 18:04:45 +0100, Heinrich Schuchardt wrote:
> >>> diff --git a/uefi-sct/SctPkg/SCRT/SCRTApp/Riscv64/GoVirtual.S
> >>> b/uefi-sct/SctPkg/SCRT/SCRTApp/Riscv64/GoVirtual.S
> >>> new file mode 100644
> >>> index 00000000..8bc2c624
> >>> --- /dev/null
> >>> +++ b/uefi-sct/SctPkg/SCRT/SCRTApp/Riscv64/GoVirtual.S
> >>> @@ -0,0 +1,45 @@
> >>> +## @file
> >>> +#
> >>> +#  Copyright 2010 - 2012 Unified EFI, Inc.<BR>
> >>> +#  Copyright (c) 2012, ARM Ltd. All rights reserved.<BR>
> >>> +#  Copyright (c) 2020, Hewlett Packard Enterprise Development LP.<BR>
> >>> +#
> >>> +#  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.
> >>> +#
> >>> +##
> >>> +#
> >>> +#
> >>> +#/*++
> >>> +#
> >>> +# Module Name:
> >>> +#
> >>> +#  GoVirtual.S
> >>> +#
> >>> +#--*/
> >>> +#start of the code section
> >>> +.text
> >>> +/* FIXME: Should alignment be different on Aarch64? */
> >>
> >> 1) FIXME
> >> 2) Aarch64.
> >
> > I have no idea why the alignment would be 3 on other platforms, so I
> > don't know how to fix it.
> > If anyone knows more, please let me know. I'll just change the comment
> > to say Riscv64.
> >
> >>> +.align 3
> 
> Both on Aarch64 and on RISC-V an odd alignment value makes no sense.
> 
> .align 8 should do no harm. But is it needed?

The glory of the GAS .align directive is that its meaning differs
between architectures and executable formats. On ARM/AArch64, as well
as on RISC-V (I think?) the alignment is described as a power of 2.

So .align 3 on ARM and others are the same as .align 8 on x86 (ELF)
and others.

(It might not be a bad idea to start replacing .align directives with
.baligh to reduce confusion.)

I haven't looked into whether 8-byte alignment is actually required by
the code here.

/
    Leif