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Re: Configuring qemu for Vector Extension

Wei Wu (吴伟)
 

Hi Mick,

As Jim said, you may need the right toolchain and right qemu for the
version you want, which is not an easy task.

BTW, the PLCT Lab is working on setting an all-in-one developer
environment for unratified extensions, including Vector.

Currently QEMU and GNU Toolchain are available. Feel free to try it out:

We cherry-pick and rebase the B/K/P/V patches and merge them into one branch.

QEMU:
https://github.com/plctlab/plct-qemu/tree/new-machine-dev

gcc:
https://github.com/pz9115/riscv-gcc/tree/riscv-gcc-experimenal-v

binutils:
https://github.com/pz9115/riscv-binutils-gdb/tree/riscv-binutils-experimental-v

It is still under development, and I hope that the PLCT Lab might be
able to provide several online QEMU VMs for public access and
experiment in 2 weeks.

On Tue, Sep 14, 2021 at 12:06 AM Jim Wilson <jimw@...> wrote:

On Sun, Sep 12, 2021 at 5:21 PM Mick Thomas Lim <mickthomaslim@...> wrote:

A "Hello World" program compiled with riscv64-unknown-linux-gnu-gcc does work.
But we aren't seeing expected behavior when running the simple rvv_vadd.c program described here:
https://lists.riscv.org/g/tech-vector-ext/message/364

There are many thousands of different incompatible draft versions of the vector spec. If you don't have exactly matching versions of the compiler and qemu and libraries, it isn't going to work. Unfortunately, it will continue to be difficult to work with the vector spec until they stop changing it in incompatible ways.

The current vector work incidentally is in clang not gcc. The gcc support may not be compatible with anything else as it hasn't been properly updated.

This is the qemu run command we're using for buildroot:
qemu-system-riscv64 -cpu rv64,x-v=true,vlen=256,elen=64,vext_spec=v0.7.1 -M virt -nographic -bios output/images/fw_jump.elf -kernel output/images/Image -append "root=/dev/vda ro" -drive file=output/images/rootfs.ext2,format=raw,id=hd0 -device virtio-blk-device,drive=hd0 -netdev user,id=net0 -device virtio-net-device,netdev=net0

The v0.7.1 draft has been obsolete for about 2 years now. That won't be useful. Unless maybe you have Alibaba compilers as this is what Alibaba implemented in their SoCs. Otherwise, you are better off with a v0.9x or v1.0 qemu. I would expect to find patches for that on the qemu mailing list. But another person pointed to a branch in a SiFive github tree that may work for you.

Jim

--
Best wishes,
Wei Wu (吴伟)
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