Add new Tier-3 target: riscv64a23-unknown-linux-gnu

[ZhongyaoChen]

MCP: Tier 3 target proposal: riscv64a23-unknown-linux-gnu

Changes:

• add new target: riscv64a23-unknown-linux-gnu
• add target page

[rustbot]

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[rustbot]

These commits modify compiler targets.
(See the Target Tier Policy.)

Some changes occurred in src/doc/rustc/src/platform-support

cc @Noratrieb

[jieyouxu]

Tier 3 targets do not get built nor tested in rust-lang/rust CI, and by implication, no prebuilt artifacts will be distributed for Tier 3 targets.

[bors]

☔ The latest upstream changes (presumably #145077) made this pull request unmergeable. Please resolve the merge conflicts.

[rustbot]

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

This PR modifies tests/ui/issues/. If this PR is adding new tests to tests/ui/issues/,
please refrain from doing so, and instead add it to more descriptive subdirectories.

This PR changes how LLVM is built. Consider updating src/bootstrap/download-ci-llvm-stamp.

This PR modifies src/bootstrap/src/core/config.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

[ZhongyaoChen]

Ready for review. @zachs18 @Noratrieb @jieyouxu

[jchzhou]

Some minor issue here: the target requirement listed in platform-support.md (kernel 4.20+, glibc 2.29) and platform-support/riscv64a23-unknown-linux-gnu.md (kernel 4.20+, glibc 2.19) does not align, and both of them are not quite sufficient for RVA23. At least the kernel should be 6.x from the last 2 or 3 years I think?

ref: https://lf-rise.atlassian.net/wiki/spaces/HOME/pages/8587962/RVA23+Profile

[ZhongyaoChen]

Some minor issue here: the target requirement listed in platform-support.md (kernel 4.20+, glibc 2.29) and platform-support/riscv64a23-unknown-linux-gnu.md (kernel 4.20+, glibc 2.19) does not align, and both of them are not quite sufficient for RVA23. At least the kernel should be 6.x from the last 2 or 3 years I think?

ref: https://lf-rise.atlassian.net/wiki/spaces/HOME/pages/8587962/RVA23+Profile

• For the minimum glibc version, riscv64gc also seems to have documentation issues. I’ll confirm the minimum version later.
• I don’t think such a new kernel is needed, since I haven’t changed ABI or std.

[ZhongyaoChen]

Pls review @jieyouxu @zachs18 @Noratrieb , i have make all changes requested.

[a4lg]

I don't support adding support for the Supm extension because of its nature. At least, support in std_detect (backend of std::arch::is_riscv_feature_detected is once rejected by @Amanieu because of this (cf. rust-lang/stdarch#1770).

This extension itself does not provide any instructions, CSRs or platform behavior constraints but only denotes existence of a platform-dependent facility to control pointer masking behavior. For instance, the Supm extension on Linux denotes prctl-based control but we can actually call prctl to probe pointer masking.

EDIT: I don't support unless it's truly necessary (e.g. for interoperability with other object files compiled for RVA23U64). Even in this case, I would like to hear your thoughts about this extension.

[a4lg]

And I have a concern regarding adding (so much) supervisor-mode extensions despite being a Linux target (which normally means a user mode target).

[a4lg]

I personally recommend starting from RVA23U64 (excluding RVA23S64) and discuss possibilities extending it later.