cmd/compile,runtime: race support for riscv64

[mauri870]

There was a previous issue requesting support for riscv64 (#58739), but it was closed because upstream support in LLVM was lacking.

On Oct 6 support for riscv64 was finally merged into the LLVM tree.

I propose we reconsider adding race detector support to Risc-V. From the top of my head this would require:

• Update the compiler to recognize -race on linux/riscv64
• clone llvm and compile a race_linux_riscv64.syso file, push the necessary changes upstream
• linux-riscv64-race builder?
• Add a new platform to x/build/cmd/racebuild to build syso files for riscv64
• Add race instrumentation (race_riscv64.s) to runtime
• Document support on https://go.dev/doc/articles/race_detector
• freebsd/riscv64 support is possible in the future?

Happy to work on this for the early stage of Go 1.23.

cc @golang/runtime @golang/riscv64

[mengzhuo]

I can setup a linux-riscv64-race builder(LUCI) for you.

[mauri870]

Thanks @mengzhuo, appreciate if you could handle that 🙏

[mauri870]

@mengzhuo I tried compiling the syso file for riscv64 with CC=clang and got stuck in this part:

runtime/race(.rodata): unexpected relocation type 291 (R_RISCV_ADD32)
runtime/race(.rodata): unsupported dynamic relocation for symbol .LBB438_37 (type=291 (R_RISCV_ADD32) stype=1 (STEXT))
runtime/race(.rodata): unexpected relocation type 295 (R_RISCV_SUB32)
runtime/race(.rodata): unsupported dynamic relocation for symbol .LJTI438_0 (type=295 (R_RISCV_SUB32) stype=9 (SRODATA))runtime/race(.rodata): unexpected relocation type 291 (R_RISCV_ADD32)
runtime/race(.rodata): unsupported dynamic relocation for symbol .LBB438_169 (type=291 (R_RISCV_ADD32) stype=1 (STEXT))
runtime/race(.rodata): unexpected relocation type 295 (R_RISCV_SUB32)
runtime/race(.rodata): unsupported dynamic relocation for symbol .LJTI438_0 (type=295 (R_RISCV_SUB32) stype=9 (SRODATA))runtime/race(.rodata): unexpected relocation type 291 (R_RISCV_ADD32)
runtime/race(.rodata): unsupported dynamic relocation for symbol .LBB438_169 (type=291 (R_RISCV_ADD32) stype=1 (STEXT))
runtime/race(.rodata): unexpected relocation type 295 (R_RISCV_SUB32)
runtime/race(.rodata): unsupported dynamic relocation for symbol .LJTI438_0 (type=295 (R_RISCV_SUB32) stype=9 (SRODATA))runtime/race(.rodata): unexpected relocation type 291 (R_RISCV_ADD32)
runtime/race(.rodata): unsupported dynamic relocation for symbol .LBB438_169 (type=291 (R_RISCV_ADD32) stype=1 (STEXT))
runtime/race(.rodata): unexpected relocation type 295 (R_RISCV_SUB32)
runtime/race(.rodata): unsupported dynamic relocation for symbol .LJTI438_0 (type=295 (R_RISCV_SUB32) stype=9 (SRODATA))runtime/race(.rodata): unexpected relocation type 291 (R_RISCV_ADD32)
runtime/race(.rodata): unsupported dynamic relocation for symbol .LBB438_169 (type=291 (R_RISCV_ADD32) stype=1 (STEXT))
runtime/race(.rodata): unexpected relocation type 295 (R_RISCV_SUB32)
runtime/race(.rodata): unsupported dynamic relocation for symbol .LJTI438_0 (type=295 (R_RISCV_SUB32) stype=9 (SRODATA))runtime/race(.rodata): unexpected relocation type 291 (R_RISCV_ADD32)
/home/ubuntu/git/go/pkg/tool/linux_riscv64/link: too many errors

Maybe I have to use some specific compiler flag? I see that these relocations are currently supported in the go linker

[mengzhuo]

CC @4a6f656c
@mauri870 builder is up, I had same issue like yours.

[4a6f656c]

@mauri870 that looks like the riscv64 linker is missing handling for some relocation types - do you have a branch handy that I can build/test from?

[mauri870]

@4a6f656c I have some changes in one of my branches, hopefully you can still build from it, if not then let me know:

https://github.com/golang/go/compare/master...mauri870:go:feature/race-riscv64?expand=1

Edit: If you wanna compile the syso file yourself, then you have to get a hold of a llvm copy and then cd compiler-rt/lib/tsan/go && CC=clang ./buildgo.sh