On Mon, Jun 27, 2022 at 4:15 PM Simon Sapin <simon.sa...@exyr.org> wrote: > > On 27/06/2022 07:40, Alistair Francis wrote: > > We have previously kept the addresses backwards compatible. So that > > software for an older virt machine will work on a newer one. There is > > currently talks about changing the virt machine memory layout in a > > breaking way and versioning in the current one though. > > > > So I don't really have a good answer for you. I would recommend > > reading as much as possible from the device tree dynamically at boot. > > > > In general though we don't want to break people, we just might have to > > make changes in the future to allow for new functionality. > > I agree that reading from the device tree as much as possible is good. We > there’s > still a need to get code running at all, and finding the device tree. > > So it would be good to decide to make stable what’s needed to get there (like > was > apparently decided for ARM) and document it.
Yeah, we are working towards that > > On principle maybe a firmware/bootloader could be entirely > position-independent? But I don't link the RISC-V toolchains suppor fully position independent code > in what I’ve done/seen so far https://docs.rs/riscv-rt/latest/riscv_rt/ has > address > ranges hard-coded in a linker script for different regions, and when passing > an ELF > file to -kernel, QEMU maps it to those addresses but boots at 0x8000_0000 > regardless. Yeah, I suspect we will keep the 0x8000_0000 as that's pretty standard > > > >> * With `qemu-system-riscv32 -machine virt -bios none -kernel something.elf > >> -s -S`, > >> GDB shows that execution starts at the lowest address of RAM, not of flash > >> like I > >> expected. Then what is emulated flash for? > > > > If you supply a flash image we will start executing from flash > > automatically. > > Passing with -drive? Should I use that instead of -kernel? If you want to pass a drive then yes, that's the better option > > > >> * To what extent is the above calling convention standardized? I found > >> similar things > >> in coreboot[4] and in OpenSBI[5] > > > > Good question. I don't think it's specified in a spec, but it is very common > > Should we document this convention as something guest code can rely on? We probably should at some point Alistair > > -- > Simon Sapin
