message: '-pacbti' is not a recognized feature for this target (ignoring feature)

[oflebbe]

When compiling for an rp2040 (with llvm13) on current dev
I get the message

'-pacbti' is not a recognized feature for this target (ignoring feature)

I guess this line is the one triggering it.

tinygo/targets/cortex-m0plus.json

Line 5 in ee497a2

"features": "+armv6-m,+soft-float,+strict-align,+thumb-mode,-aes,-bf16,-cdecp0,-cdecp1,-cdecp2,-cdecp3,-cdecp4,-cdecp5,-cdecp6,-cdecp7,-crc,-crypto,-d32,-dotprod,-dsp,-fp-armv8,-fp-armv8d16,-fp-armv8d16sp,-fp-armv8sp,-fp16,-fp16fml,-fp64,-fpregs,-fullfp16,-hwdiv,-hwdiv-arm,-i8mm,-lob,-mve,-mve.fp,-neon,-pacbti,-ras,-sb,-sha2,-vfp2,-vfp2sp,-vfp3,-vfp3d16,-vfp3d16sp,-vfp3sp,-vfp4,-vfp4d16,-vfp4d16sp,-vfp4sp"

However if I check https://community.arm.com/arm-community-blogs/b/architectures-and-processors-blog/posts/armv8-1-m-pointer-authentication-and-branch-target-identification-extension this feature is an ARM8 extension and isn't available on 32bit targets. Is this added accidentely ? @aykevl ?

[aykevl]

It has a - in front of it so it disables this feature. So that's correct.

This feature is new in LLVM 14. Updating to LLVM 14 (build tinygo with -tags=llvm14) will get the feature recognized and will let the warning disappear. I've added -pacbti to match Clang because if it doesn't match Clang, LLVM refuses to inline such functions between C and Go.

[ysoldak]

I think we have to wait for llvm@14 on Mac to test that.
There is an open PR Homebrew/homebrew-core#97618

(assuming we want to use system llvm, instead of building own, that is)

[QuLogic]

This feature is new in LLVM 14.

I suppose this means I can patch out the -pacbti on our LLVM 13 builds then?

[aykevl]

Yes, that's fine.

(I know it's not a great solution, but I'm not sure what's the best way to fix this).

[QuLogic]

For LLVM 13, what I did was QuLogic@1e77b52, which you may want to use for packages.

However, #3039 has dropped support for LLVM 13, so I guess this can be closed.

[aykevl]

For LLVM 13, what I did was QuLogic@1e77b52, which you may want to use for packages.

That's a workaround if you encounter a similar issue again, but note that it if this patch is applied for LLVM 14 as well it will block inlining between C and Go code. That might not be what you intended.

[QuLogic]

Yes, it's only for LLVM 13.