RISC-V requires "zicsr" ISA extension to build with FSF GNAT 12.1.1

Question

RISC-V requires "zicsr" ISA extension to build with FSF GNAT 12.1.1

rod-chapman opened this issue 2 years ago · comments

A recent change in GNU binutils (see https://groups.google.com/a/groups.riscv.org/g/sw-dev/c/aE1ZeHHCYf4) means that the RISC-V "performance counter" registers are now in a specific ISA extension called "zicsr". This change is shipping with the FSF GNAT 12.1.1 in Alire, so the build of Ada_Drivers_Library for the HiFive_revb (for example) fails. The project files needs to be updated to select "-march=rv32imac_zicsr" for all units, or (more generally) to add "_zicsr" to the end of the "-march" option for units that require the CSRR instructions.

Roderick Chapman · Answer 1 · Thu Jun 30 2022 17:26:22 GMT+0800 (China Standard Time)

It may also be possible to directly insert an assembler directive in the generated code for the packages that require the CSRR and CSRW instructions. I think you need to add
.option arch,+zicsr

near the top of the generated .s file. Can this be done with package Machine_Code?

Details in the RISC-V specific section of the most recent GNU as manual.

Roderick Chapman · Answer 2 · Thu Jun 30 2022 17:51:26 GMT+0800 (China Standard Time)

For reference, my local changes to SPARKNaCl to get GNAT 12.1.1 working are here:
rod-chapman/SPARKNaCl#28

Fabien Chouteau · Answer 3 · Thu Jun 30 2022 20:28:55 GMT+0800 (China Standard Time)

.option arch,+zicsr in inlined machine code would be the best option in my opinion. Did you try it?

Roderick Chapman · Answer 4 · Thu Jun 30 2022 20:38:54 GMT+0800 (China Standard Time)

Yes... but I couldn't work out the exact syntax required...

See https://sourceware.org/binutils/docs/as/RISC_002dV_002dDirectives.html#RISC_002dV_002dDirectives

Fabien Chouteau · Answer 5 · Fri Jul 01 2022 16:33:50 GMT+0800 (China Standard Time)

Might be because we don't have the latest binutils: enjoy-digital/litex@91d79ae

I will build a toolchain with the latest and try again.

Fabien Chouteau · Answer 6 · Fri Jul 01 2022 18:24:11 GMT+0800 (China Standard Time)

Confirmed, I started build for a new release of the toolchains with binutils 2.38.

Roderick Chapman · Answer 7 · Mon Jul 04 2022 16:20:18 GMT+0800 (China Standard Time)

OK... let me know when it's ready (and how to get it) and I will give it a try...

Roderick Chapman · Answer 8 · Tue Jul 05 2022 22:16:42 GMT+0800 (China Standard Time)

Reading the ISA spec more carefully, I think you actually should generate

.option push
.option arch,+zicsr
# do stuff with CSRs or whatever...
.option pop

so that the existing state of the "arch" setting is saved and restored properly.

Roderick Chapman · Answer 9 · Fri Jul 22 2022 22:41:27 GMT+0800 (China Standard Time)

The SPARKNaCl performance test program now seems to build OK with the new GNAT 12.1.2 with no modification to the assembly language component(s), so looking good.

Fabien Chouteau · Answer 10 · Fri Jul 22 2022 23:05:22 GMT+0800 (China Standard Time)

Without the .option arch,+zicsr?

Thanks for the update,

Roderick Chapman · Answer 11 · Fri Jul 22 2022 23:34:51 GMT+0800 (China Standard Time)

Yes... my sources (see SPARKNaCl/perf/csrs.s) are unmodified and it builds OK...