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Booting OS images

The Sail model implements a very simple platform based on the one implemented by the Spike reference simulator. It implements a console output port similar to Spike's HTIF (host-target interface) mechanism, and an interrupt controller based on Spike's CLINT (core-local interrupt controller). Console input is not currently supported.

32-bit OS boots require a workaround for the 64-bit HTIF interface, which is currently not supported.

OS boots use device-tree binary blobs generated by the dtc compiler, installable on Ubuntu and Debian machines with

sudo apt install device-tree-compiler

Booting Linux with the C backend

The C model needs an ELF-version of the BBL (Berkeley-Boot-Loader) that contains the Linux kernel as an embedded payload. It also needs a DTB (device-tree blob) file describing the platform (say in the file spike.dtb). Once those are available (see below for suggestions), the model should be run as:

$ ./c_emulator/riscv_sim_<arch> -t console.log -b spike.dtb bbl > execution-trace.log 2>&1 &
$ tail -f console.log

The console.log file contains the console boot messages. For maximum performance and benchmarking a model without any execution tracing is available on the optimize branch (git checkout optimize) of this repository. This currently requires the latest Sail built from source.

Booting Linux with the OCaml backend

The OCaml model only needs the ELF-version of the BBL, since it can generate its own DTB.

$ ./ocaml_emulator/riscv_ocaml_sim_<arch> bbl > execution-trace.log 2> console.log

Caveats for OS boot

  • Some OS toolchains generate obsolete LR/SC instructions with now illegal combinations of .aq and .rl flags. You can work-around this by changing riscv_mem.sail to accept these flags.

  • One needs to manually ensure that the DTB used for the C model accurately describes the physical memory map implemented in the C platform. This will not be needed once the C model can generate its own DTB.

Sample Linux image

rv64-linux-4.15.0-gcc-7.2.0-64mb.bbl contains a sample Linux RV64 image that can be booted as follows, after first generating the device-tree blob for a 64MB RV64 machine using dtc:

dtc < os-boot/rv64-64mb.dts > os-boot/rv64-64mb.dtb
./c_emulator/riscv_sim_RV64 -b os-boot/rv64-64mb.dtb -t /tmp/console.log os-boot/rv64-linux-4.15.0-gcc-7.2.0-64mb.bbl > >(gzip -c > execution-trace.log.gz) 2>&1
tail -f /tmp/console.log