Add configuration for gcc 16.1 baremetal toolchain and add compatibility fix for RISC-V proxy kernel

[isa084]

The PR adds the following features to fix the issue mentioned in #3356 :

1. Add a new toolchain configuration for building gcc 16.1, compatible with the instructions in util/toolchain-builder.
2. Update the riscv-pk installation script to a recent version compatible with gcc > 15. Without this update, the riscv-pk installation fails due to tighter compiler warnings flagged by gcc versions higher than 15.

The final outcome is that users can now :

1. Build RISC-V GNU toolchain with gcc 16.1 using the existing toolchain-builder.
2. Run programs compiled with gcc > 15 on veri-testharness-pk simulation target.

• I have searched for similar pull requests
• I am a human engaging in an interpersonal interaction. During this interaction, my words are my own and are not generated. If relevant, I provide links to my sources.

[MikeOpenHWGroup]

As an aside, I used the above compiler version to launch verif/regress/coremark.sh and got total ticks = 229114.

Hi @isa084, please do not introduce multiple topics into a single issue or pull-request. This PR is about the gcc 16.1 baremetal toolchain. If you'd like to ask a question about coremark please do so in a new/different Issue. If GitHub is not a good fit for the discussion, consider posting a question to the CVA6 channel on MatterMost.

[isa084]

@MikeOpenHWGroup Sorry about that !

I will open another issue or post it on the CVA6 channel on Mattermost

[valentinThomazic]

Hi @isa084
We need to install GCC 16 on Thales CI runners to test the PR.
I will let you know when it is done!

[zchamski]

Hi @isa084,

When we upgraded the CVA6 GCC baseline to version 15, the move (and the asociated effort) was motivated by a notable improvement in benchmark perfomance, especially on CoreMark. Does GCC 16 bring any significant benefits in target feature support /perf / code size compared to GCC 15?

[isa084]

@zchamski from my past experience with ARM/RISC-V cores, there is no guarantee that merely upgrading the compiler will lead to performance improvements. I am in interested in investigating this further, once the above PR is accepted.

[JeanRochCoulon]

Hello @isa084
Lot of different tools are needed to support CVA6 functionalities: Spike, compilers, Verilator, VCS, Questa, Synthesis tool, Power tools, FPGA tools, ... Upgrading tool requests effort. We will upgrade GCC in the case there is an interest.

[JeanRochCoulon]

To demonstrate the performance improvements, coremark job can be used. With GCC15, we are currently at 5 Coremark/MHz.