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os-boot

README.md

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.

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