On Mon, 13 May 2019, Atish Patra wrote: > On 5/13/19 3:31 PM, Paul Walmsley wrote: > > 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.pa...@wdc.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. > > > That would be inventing our RISC-V specific header format. However, we > can always use the one of the reserved fields in proposed header (res4) > for this purpose.
What are the semantics of those reserved fields? > Do we need to add it now or add it later when we actually need a version > number. My preference is to add it later based on requirement. If it isn't added now, how would bootloaders know whether it was there or not? - Paul
