Add features gates for experimental asm features #90348

Amanieu · 2021-10-27T17:43:04Z

This PR splits off parts of asm! into separate features because they are not ready for stabilization.

Specifically this adds:

asm_const for const operands.
asm_sym for sym operands.
asm_experimental_arch for architectures other than x86, x86_64, arm, aarch64 and riscv.

r? @nagisa

joshtriplett · 2021-10-30T21:53:13Z

Looks reasonable to me. r=me once it passes CI.

Amanieu · 2021-11-01T21:00:49Z

@bors r=joshtriplett

bors · 2021-11-01T21:00:51Z

📌 Commit 53ff09f123d246c2e86ce9aba39027b9dfa82009 has been approved by joshtriplett

bors · 2021-11-02T07:47:57Z

⌛ Testing commit 53ff09f123d246c2e86ce9aba39027b9dfa82009 with merge 5f7f78f5227ff3342c84fe250ac1e9b31a908c51...

bors · 2021-11-02T08:11:53Z

💔 Test failed - checks-actions

bors · 2021-11-03T05:32:04Z

☔ The latest upstream changes (presumably #90516) made this pull request unmergeable. Please resolve the merge conflicts.

Amanieu · 2021-11-03T12:27:11Z

@bors r=joshtriplett rollup=iffy

bors · 2021-11-07T01:54:17Z

📌 Commit b88821c5abbc65dfb17eff7094b4b05e9ed523e6 has been approved by joshtriplett

bors · 2021-11-07T01:54:27Z

⌛ Testing commit b88821c5abbc65dfb17eff7094b4b05e9ed523e6 with merge b0ee314d7a7490dd02bd701d23b5396c8b817e02...

bors · 2021-11-07T02:17:31Z

💔 Test failed - checks-actions

architectures

Amanieu · 2021-11-07T03:44:53Z

@bors r=joshtriplett

bors · 2021-11-07T03:44:54Z

📌 Commit 87d0d64 has been approved by joshtriplett

bors · 2021-11-07T04:59:46Z

⌛ Testing commit 87d0d64 with merge 90a273b...

bors · 2021-11-07T07:56:43Z

☀️ Test successful - checks-actions
Approved by: joshtriplett
Pushing 90a273b to master...

rust-timer · 2021-11-07T09:27:28Z

Finished benchmarking commit (90a273b): comparison url.

Summary: This benchmark run did not return any relevant changes.

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression

bnaecker · 2021-11-08T23:59:19Z

I know this has already been merged, but I'm a bit concerned about this change. For context, I maintain the usdt crate, which allows developers to insert DTrace probes into userland Rust code. For a variety of reasons, that crate works by generating declarative macros (macros-by-example) for each probe, whose expanded bodies contain inline assembly. Because the expansion site contains asm!, which requires a feature flag, developers using the usdt crate have previously been required to include a #![feature(asm)] in their own code that defines and uses probes. As of this change, there are now two features required for downstream users of the usdt crate, asm and (at least on macOS platforms), asm_sym.

More generally, this manner in which this new flag was included seems fraught. As I understand it, any code with a call to asm! that uses a symbol operand will not compile across this threshold. Existing code has been effectively hidden behind a new feature flag.

I'm not sure how to resolve this. Since there is no support for compile-time detection of the Rust toolchain (that I'm aware of!), it doesn't seem possible to write a library that uses symbol operands, and that can be compiled across this change. Including the asm_sym flag will generate compiler errors on an older toolchain, since that feature flag is unknown in that case. But omitting the asm_sym flag will generate compiler errors on this toolchain. How can one write the set of feature flags required to build such a library for a range of compiler versions?

cc @ahl

…=Mark-Simulacrum kmc-solid: Avoid the use of `asm_const` This PR removes the use of [the now-separated-out `asm_const` compiler feature][1] in `std::sys::solid` to fix the [`*-kmc-solid_*`](https://doc.rust-lang.org/nightly/rustc/platform-support/kmc-solid.html) Tier 3 targets. [1]: rust-lang#90348

rust-highfive assigned nagisa Oct 27, 2021

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 27, 2021