Update README for new CMake build system

[Alasdair]

I think the README needs to be updated for the new CMake build system as says:

make -C build riscv_sim_rv64f_rvfi

but this doesn't work until you've run CMake at least to get the build directory. I think the intent behind the current wording is to run the build_simulators.sh script first, but I don't think this is obvious enough.

[Timmmm]

Hmm I couldn't think of a good way to word this so what if we just change the code block to this?

$ ./build_simulators.sh
$ make -C build riscv_sim_rv64f_rvfi

[jordancarlin]

What about having the first line directly invoke cmake to avoid unnecessarily building the standard simulators first?

[Timmmm]

That gets a bit complex for a first command the user ever runs maybe...

mkdir -p build
cmake -S . -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo -DDOWNLOAD_GMP=TRUE
make -C build riscv_sim_rv64f_rvfi

[jordancarlin]

The mkdircommand shouldn’t be needed (cmake creates that directory automatically).

That gets a bit complex for a first command the user ever runs maybe...

I assume most users won’t be using the rvfi version, so not sure that this is a huge concern. Also, once we have the pre-compiled releases I think we should change this section to direct users to those and have a separate developers (or something along those lines) section that explains how to actually build the model. Most people should not need to build from source themselves.

[Timmmm]

So this?

cmake -S . -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo -DDOWNLOAD_GMP=TRUE
make -C build riscv_sim_rv64f_rvfi

I'm ok with that if you guys think it is better.

[jordancarlin]

So this?

cmake -S . -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo -DDOWNLOAD_GMP=TRUE
make -C build riscv_sim_rv64f_rvfi

That’s what I was thinking. I think we should definitely go with one of the options discussed in this thread, and this one would be my preference to avoid redundant/unnecessary compilation, but I’d be fine with either.