[PATCH] D110065: [AArch64] Add support for the 'R' architecture profile.

Thu Sep 30 11:03:01 PDT 2021

nickdesaulniers added a comment.

In D110065#3033050 <https://reviews.llvm.org/D110065#3033050>, @labrinea wrote:

> That said my current approach will be breaking the current tools behavior: when the user only specifies the triple and not -march then they will be targeting the intersection, not v8-a.

For the purposes of compiling the linux kernel, for the `ARCH=arm64` port, we always pass `-Wa,-march=armv8.5-a` but not `-march=`.  While it's trivial to add it to the kernel Makefiles, I worry if this causes clang's behavior to differ significantly from GCC. Does GCC support the R profile?

> The impact is not expected to be significant as the missing instructions (smc, dcps3) were not being generated anyway.

I can see in the kernel sources that hypervisor code in KVM is using `smc` instructions. `kvm/hyp/hyp-entry.S`  Since we're passing `-Wa,-march=`, I suspect with your patch we'd be fine.

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