expose is_s390x_feature_detected! from std::arch

[folkertdev]

tracking issue: #135413
implementation: rust-lang/stdarch#1699 (more features added in rust-lang/stdarch#1720)

This macro was part of the recent stdarch synchronization, but not yet exposed via std::arch.

r? libs

[Mark-Simulacrum]

@bors r+

Technically new API area, but seems basically obviously fine to add as unstable.

[bors]

📌 Commit a312635 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[uweigand]

Not sure if this is directly related, but as of a few days ago, I now see this failure in ./x.py check:

...
9   |           $(cfg!(target_feature = $target_feature_lit) ||)*
    |                  ^^^^^^^^^^^^^^
...
50  | /         macro_rules! $macro_name {
51  | |             $(
52  | |                 ($feature_lit) => {
53  | |                     $crate::detect_feature!($feature, $feature_lit $(, without cfg check: $feature_cfg_check)? $(: $($target_feature_lit),*)?)
    | |                     -------------------------------------------------------------------------------------------------------------------------- in this macro invocation (#2)
...   |
87  | |             };
88  | |         }
    | |_________- in this expansion of `is_s390x_feature_detected!` (#1)
    |
   ::: library/std/tests/run-time-detect.rs:154:9
    |
154 |           is_s390x_feature_detected!("vector-packed-decimal-enhancement-2")
    |           ----------------------------------------------------------------- in this macro invocation (#1)
    |
    = note: expected values for `target_feature` are: `10e60`, `2e3`, `3e3r1`, `3e3r2`, `3e3r3`, `3e7`, `7e10`, `a`, `aclass`, `adx`, `aes`, `altivec`, `alu32`, `amx-bf16`, `amx-complex`, `amx-fp16`, `amx-int8`, `amx-tile`, `atomics`, `avx`, `avx2`, `avx512bf16`, `avx512bitalg`, `avx512bw`, `avx512cd`, `avx512dq`, `avx512f`, `avx512fp16`, `avx512ifma`, `avx512vbmi`, `avx512vbmi2`, `avx512vl`, `avx512vnni`, `avx512vp2intersect`, and `avx512vpopcntdq` and 266 more
    = note: using a cfg inside a macro will use the cfgs from the destination crate and not the ones from the defining crate
    = help: try referring to `$crate::detect_feature` crate for guidance on how handle this unexpected cfg
    = help: the macro `$crate::detect_feature` may come from an old version of the `std_detect` crate, try updating your dependency with `cargo update -p std_detect`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration

error: unexpected `cfg` condition value: `vector-packed-decimal-enhancement`
   --> /home/stefansf/devel/dailyrust-workdir/rust/library/stdarch/crates/std_detect/src/detect/macros.rs:9:16
    |
4   |   macro_rules! detect_feature {
    |   ---------------------------
    |   |
    |   in this expansion of `$crate::detect_feature!` (#2)
    |   in this expansion of `$crate::detect_feature!` (#3)
5   |       ($feature:tt, $feature_lit:tt) => {
6   |           $crate::detect_feature!($feature, $feature_lit : $feature_lit)
    |           -------------------------------------------------------------- in this macro invocation (#3)
...
9   |           $(cfg!(target_feature = $target_feature_lit) ||)*
    |                  ^^^^^^^^^^^^^^
...
50  | /         macro_rules! $macro_name {
51  | |             $(
52  | |                 ($feature_lit) => {
53  | |                     $crate::detect_feature!($feature, $feature_lit $(, without cfg check: $feature_cfg_check)? $(: $($target_feature_lit),*)?)
    | |                     -------------------------------------------------------------------------------------------------------------------------- in this macro invocation (#2)
...   |
87  | |             };
88  | |         }
    | |_________- in this expansion of `is_s390x_feature_detected!` (#1)
    |
   ::: library/std/tests/run-time-detect.rs:158:9
    |
158 |           is_s390x_feature_detected!("vector-packed-decimal-enhancement")
    |           --------------------------------------------------------------- in this macro invocation (#1)
    |
    = note: expected values for `target_feature` are: `10e60`, `2e3`, `3e3r1`, `3e3r2`, `3e3r3`, `3e7`, `7e10`, `a`, `aclass`, `adx`, `aes`, `altivec`, `alu32`, `amx-bf16`, `amx-complex`, `amx-fp16`, `amx-int8`, `amx-tile`, `atomics`, `avx`, `avx2`, `avx512bf16`, `avx512bitalg`, `avx512bw`, `avx512cd`, `avx512dq`, `avx512f`, `avx512fp16`, `avx512ifma`, `avx512vbmi`, `avx512vbmi2`, `avx512vl`, `avx512vnni`, `avx512vp2intersect`, and `avx512vpopcntdq` and 266 more
    = note: using a cfg inside a macro will use the cfgs from the destination crate and not the ones from the defining crate
    = help: try referring to `$crate::detect_feature` crate for guidance on how handle this unexpected cfg
    = help: the macro `$crate::detect_feature` may come from an old version of the `std_detect` crate, try updating your dependency with `cargo update -p std_detect`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration

error: unexpected `cfg` condition value: `vector-packed-decimal`
   --> /home/stefansf/devel/dailyrust-workdir/rust/library/stdarch/crates/std_detect/src/detect/macros.rs:9:16
    |
4   |   macro_rules! detect_feature {
    |   ---------------------------
    |   |
    |   in this expansion of `$crate::detect_feature!` (#2)
    |   in this expansion of `$crate::detect_feature!` (#3)
5   |       ($feature:tt, $feature_lit:tt) => {
6   |           $crate::detect_feature!($feature, $feature_lit : $feature_lit)
    |           -------------------------------------------------------------- in this macro invocation (#3)
...
9   |           $(cfg!(target_feature = $target_feature_lit) ||)*
    |                  ^^^^^^^^^^^^^^
...
50  | /         macro_rules! $macro_name {
51  | |             $(
52  | |                 ($feature_lit) => {
53  | |                     $crate::detect_feature!($feature, $feature_lit $(, without cfg check: $feature_cfg_check)? $(: $($target_feature_lit),*)?)
    | |                     -------------------------------------------------------------------------------------------------------------------------- in this macro invocation (#2)
...   |
87  | |             };
88  | |         }
    | |_________- in this expansion of `is_s390x_feature_detected!` (#1)
    |
   ::: library/std/tests/run-time-detect.rs:160:43
    |
160 |       println!("vector-packed-decimal: {}", is_s390x_feature_detected!("vector-packed-decimal"));
    |                                             --------------------------------------------------- in this macro invocation (#1)
    |
    = note: expected values for `target_feature` are: `10e60`, `2e3`, `3e3r1`, `3e3r2`, `3e3r3`, `3e7`, `7e10`, `a`, `aclass`, `adx`, `aes`, `altivec`, `alu32`, `amx-bf16`, `amx-complex`, `amx-fp16`, `amx-int8`, `amx-tile`, `atomics`, `avx`, `avx2`, `avx512bf16`, `avx512bitalg`, `avx512bw`, `avx512cd`, `avx512dq`, `avx512f`, `avx512fp16`, `avx512ifma`, `avx512vbmi`, `avx512vbmi2`, `avx512vl`, `avx512vnni`, `avx512vp2intersect`, and `avx512vpopcntdq` and 266 more
    = note: using a cfg inside a macro will use the cfgs from the destination crate and not the ones from the defining crate
    = help: try referring to `$crate::detect_feature` crate for guidance on how handle this unexpected cfg
    = help: the macro `$crate::detect_feature` may come from an old version of the `std_detect` crate, try updating your dependency with `cargo update -p std_detect`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration

error: could not compile `std` (test "run-time-detect") due to 11 previous errors
warning: build failed, waiting for other jobs to finish...
Build completed unsuccessfully in 0:00:30

[folkertdev]

I suspect this is a caching issue of some kind? I ran run the following just fine (with qemu)

#![cfg_attr(
    all(target_arch = "s390x", target_os = "linux"),
    feature(stdarch_s390x_feature_detection)
)]

use std::arch::is_s390x_feature_detected;
fn main() {
    println!(
        "vector-packed-decimal-enhancement-2: {}",
        is_s390x_feature_detected!("vector-packed-decimal-enhancement-2")
    );
}

on current nightly. You could try a ./x clean maybe? (I'm assuming you are on a commit that should have this macro exposed?)

[uweigand]

I still see the failure today after cleaning everything. The failure occurs during stage0 library build, where the std library sources included in the Rust repo (rust/library/std) are being built with the bootstrap compiler (https://static.rust-lang.org/dist/2025-02-18/rustc-beta-s390x-unknown-linux-gnu.tar.xz). Is this supposed to work now?

[folkertdev]

I believe bootstrap updates in tandem with the standard releases, so maybe wait for that?

[uweigand]

I believe bootstrap updates in tandem with the standard releases, so maybe wait for that?

I just ran ./x.py run src/tools/bump-stage0 and the build is now using https://static.rust-lang.org/dist/2025-03-23/rustc-beta-s390x-unknown-linux-gnu.tar.xz. But I'm still getting the same error ...

I suspect something else must be going on here. A minimal command line to reproduce is

RUSTC_BOOTSTRAP=1 /home/uweigand/rust/build/s390x-unknown-linux-gnu/stage0/bin/rustc
library/std/tests/run-time-detect.rs --test --target s390x-unknown-linux-gnu
--check-cfg "cfg(test)" -D unexpected-cfgs
--sysroot /home/uweigand/rust/build/s390x-unknown-linux-gnu/stage0-sysroot

where /home/uweigand/rust/build/s390x-unknown-linux-gnu/stage0/bin/rustc is (after my change) version rustc 1.86.0-beta.7 (7824ede68 2025-03-22), and /home/uweigand/rust/build/s390x-unknown-linux-gnu/stage0-sysroot contains a lib/rustlib/s390x-unknown-linux-gnu/lib/libstd-743ebc1720e92b95.rmeta that was apparently just rebuilt from mainline sources using that same 2025-03-22 compiler. This should all be recent enough, shouldn't it?

[folkertdev]

The build of stage0 appears new enough, but does not contain all commits of the master branch. Only critical bug fixes are backported (e.g. see this PR to beta which that commit is a part of #138817).

So modulo these beta backports, the code used for bootstrap should only update every 6 weeks. The next release is in roughly 7 days, so I expect these issues to be resolved early next week.

I did ask some further questions here #t-libs > target features, core_arch and bootstrap, because another sync from core_arch to rust/rust also caused issues with these tests. It still looks like the next release cycle should resolve these issues.

The true problem here is that stdarch and rust-lang/rust are in different repositories. There are some plans to change that, but it's tricky and has downsides too.

[uweigand]

The build of stage0 appears new enough, but does not contain all commits of the master branch. Only critical bug fixes are backported (e.g. see this PR to beta which that commit is a part of #138817).

Oh, so the stage0 compiler binaries were created on 2025-03-22, but from the beta branch, not master. That's the bit I was missing - thanks!