linux-kernel - Re: [v2 PATCH] RISC-V: Add a PE/COFF compliant Image header.

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Message-ID: <alpine.DEB.2.21.9999.1905131522370.21198@viisi.sifive.com>
Date:   Mon, 13 May 2019 15:31:16 -0700 (PDT)
From:   Paul Walmsley <paul.walmsley@...ive.com>
To:     Atish Patra <atish.patra@....com>
cc:     linux-kernel@...r.kernel.org, mark.rutland@....com,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Zong Li <zong@...estech.com>, merker@...ian.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [v2 PATCH] RISC-V: Add a PE/COFF compliant Image header.

On Wed, 1 May 2019, Atish Patra wrote:

> Currently, last stage boot loaders such as U-Boot can accept only
> uImage which is an unnecessary additional step in automating boot flows.
> 
> Add a PE/COFF compliant image header that boot loaders can parse and
> directly load kernel flat Image. The existing booting methods will continue
> to work as it is.
> 
> Another goal of this header is to support EFI stub for RISC-V in future.
> EFI specification needs PE/COFF image header in the beginning of the kernel
> image in order to load it as an EFI application. In order to support
> EFI stub, code0 should be replaced with "MZ" magic string and res5(at
> offset 0x3c) should point to the rest of the PE/COFF header (which will
> be added during EFI support).
> 
> Tested on both QEMU and HiFive Unleashed using OpenSBI + U-Boot + Linux.
> 
> Signed-off-by: Atish Patra <atish.patra@....com>

Seems like we're stuck with this basic format for EFI, etc.  Even though 
we may be stuck with it, I think we should take the opportunity to add the 
possibility to extending this header format by adding fields after the 
basic PE/COFF header ends.

In particular, at the very least, I'd suggest adding a u32 after the 
PE/COFF header ends, to represent a "RISC-V header format version number".  
Then if we add more fields that follow the PE/COFF header -- for example, 
to represent the RISC-V instruction set extensions that are required to 
run this binary -- we can just bump that RISC-V-specific version number 
field to indicate to bootloaders that there's more there.

One other observation - if what's here was copied from some other 
architecture, like ARM, please acknowledge the source in the patch 
description.

thanks

- Paul