forbid toggling x87 and fpregs on hard-float targets

Author: RalfJung

compiler/rustc_feature/src/unstable.rs

@@ -342,6 +342,7 @@ declare_features! (
     (unstable, sse4a_target_feature, "1.27.0", Some(44839)),
     (unstable, tbm_target_feature, "1.27.0", Some(44839)),
     (unstable, wasm_target_feature, "1.30.0", Some(44839)),
+    (unstable, x87_target_feature, "CURRENT_RUSTC_VERSION", Some(44839)),
     // !!!!    !!!!    !!!!    !!!!   !!!!    !!!!    !!!!    !!!!    !!!!    !!!!    !!!!
     // Features are listed in alphabetical order. Tidy will fail if you don't keep it this way.
     // !!!!    !!!!    !!!!    !!!!   !!!!    !!!!    !!!!    !!!!    !!!!    !!!!    !!!!

compiler/rustc_span/src/symbol.rs

@@ -2176,6 +2176,7 @@ symbols! {
         writeln_macro,
         x86_amx_intrinsics,
         x87_reg,
+        x87_target_feature,
         xer,
         xmm_reg,
         xop_target_feature,

compiler/rustc_target/src/spec/mod.rs

@@ -2594,6 +2594,18 @@ impl TargetOptions {
                 .collect();
         }
     }
+
+    pub(crate) fn has_feature(&self, search_feature: &str) -> bool {
+        self.features.split(',').any(|f| {
+            if let Some(f) = f.strip_prefix('+')
+                && f == search_feature
+            {
+                true
+            } else {
+                false
+            }
+        })
+    }
 }
 
 impl Default for TargetOptions {

compiler/rustc_target/src/target_features.rs

@@ -32,6 +32,8 @@ pub enum Stability<AllowToggle> {
     /// This target feature is unstable. It is only present in `#[cfg(target_feature)]` on
     /// nightly and using it in `#[target_feature]` requires enabling the given nightly feature.
     Unstable {
+        /// This must be a *language* feature, or else rustc will ICE when reporting a missing
+        /// feature gate!
         nightly_feature: Symbol,
         /// See `Stable::allow_toggle` comment above.
         allow_toggle: AllowToggle,
@@ -168,6 +170,22 @@ const ARM_FEATURES: &[(&str, StabilityUncomputed, ImpliedFeatures)] = &[
     ("dotprod", unstable(sym::arm_target_feature), &["neon"]),
     ("dsp", unstable(sym::arm_target_feature), &[]),
     ("fp-armv8", unstable(sym::arm_target_feature), &["vfp4"]),
+    (
+        "fpregs",
+        Stability::Unstable {
+            nightly_feature: sym::arm_target_feature,
+            allow_toggle: |target: &Target| {
+                // Only allow toggling this if the target has `soft-float` set. With `soft-float`,
+                // `fpregs` isn't needed so changing it cannot affect the ABI.
+                if target.has_feature("soft-float") {
+                    Ok(())
+                } else {
+                    Err("unsound on hard-float targets because it changes float ABI")
+                }
+            },
+        },
+        &[],
+    ),
     ("i8mm", unstable(sym::arm_target_feature), &["neon"]),
     ("mclass", unstable(sym::arm_target_feature), &[]),
     ("neon", unstable(sym::arm_target_feature), &["vfp3"]),
@@ -191,7 +209,6 @@ const ARM_FEATURES: &[(&str, StabilityUncomputed, ImpliedFeatures)] = &[
     ("vfp4", unstable(sym::arm_target_feature), &["vfp3"]),
     ("virtualization", unstable(sym::arm_target_feature), &[]),
     // tidy-alphabetical-end
-    // FIXME: need to also forbid turning off `fpregs` on hardfloat targets
 ];
 
 const AARCH64_FEATURES: &[(&str, StabilityUncomputed, ImpliedFeatures)] = &[
@@ -444,13 +461,28 @@ const X86_FEATURES: &[(&str, StabilityUncomputed, ImpliedFeatures)] = &[
     ("tbm", unstable(sym::tbm_target_feature), &[]),
     ("vaes", unstable(sym::avx512_target_feature), &["avx2", "aes"]),
     ("vpclmulqdq", unstable(sym::avx512_target_feature), &["avx", "pclmulqdq"]),
+    (
+        "x87",
+        Stability::Unstable {
+            nightly_feature: sym::x87_target_feature,
+            allow_toggle: |target: &Target| {
+                // Only allow toggling this if the target has `soft-float` set. With `soft-float`,
+                // `fpregs` isn't needed so changing it cannot affect the ABI.
+                if target.has_feature("soft-float") {
+                    Ok(())
+                } else {
+                    Err("unsound on hard-float targets because it changes float ABI")
+                }
+            },
+        },
+        &[],
+    ),
     ("xop", unstable(sym::xop_target_feature), &[/*"fma4", */ "avx", "sse4a"]),
     ("xsave", STABLE, &[]),
     ("xsavec", STABLE, &["xsave"]),
     ("xsaveopt", STABLE, &["xsave"]),
     ("xsaves", STABLE, &["xsave"]),
     // tidy-alphabetical-end
-    // FIXME: need to also forbid turning off `x87` on hardfloat targets
 ];
 
 const HEXAGON_FEATURES: &[(&str, StabilityUncomputed, ImpliedFeatures)] = &[

tests/ui/check-cfg/mix.stderr

@@ -251,7 +251,7 @@ warning: unexpected `cfg` condition value: `zebra`
 LL |     cfg!(target_feature = "zebra");
    |          ^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = 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 251 more
+   = 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 253 more
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
 
 warning: 27 warnings emitted

tests/ui/check-cfg/well-known-values.stderr

@@ -174,7 +174,7 @@ warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
 LL |     target_feature = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = 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`, `avx512vpopcntdq`, `avxifma`, `avxneconvert`, `avxvnni`, `avxvnniint16`, `avxvnniint8`, `backchain`, `bf16`, `bmi1`, `bmi2`, `bti`, `bulk-memory`, `c`, `cache`, `cmpxchg16b`, `crc`, `crt-static`, `cssc`, `d`, `d32`, `dit`, `doloop`, `dotprod`, `dpb`, `dpb2`, `dsp`, `dsp1e2`, `dspe60`, `e`, `e1`, `e2`, `ecv`, `edsp`, `elrw`, `ermsb`, `exception-handling`, `extended-const`, `f`, `f16c`, `f32mm`, `f64mm`, `faminmax`, `fcma`, `fdivdu`, `fhm`, `flagm`, `flagm2`, `float1e2`, `float1e3`, `float3e4`, `float7e60`, `floate1`, `fma`, `fp-armv8`, `fp16`, `fp64`, `fp8`, `fp8dot2`, `fp8dot4`, `fp8fma`, `fpuv2_df`, `fpuv2_sf`, `fpuv3_df`, `fpuv3_hf`, `fpuv3_hi`, `fpuv3_sf`, `frecipe`, `frintts`, `fxsr`, `gfni`, `hard-float`, `hard-float-abi`, `hard-tp`, `hbc`, `high-registers`, `hvx`, `hvx-length128b`, `hwdiv`, `i8mm`, `jsconv`, `lahfsahf`, `lasx`, `lbt`, `leoncasa`, `lor`, `lse`, `lse128`, `lse2`, `lsx`, `lut`, `lvz`, `lzcnt`, `m`, `mclass`, `mops`, `movbe`, `mp`, `mp1e2`, `msa`, `mte`, `multivalue`, `mutable-globals`, `neon`, `nontrapping-fptoint`, `nvic`, `paca`, `pacg`, `pan`, `partword-atomics`, `pauth-lr`, `pclmulqdq`, `pmuv3`, `popcnt`, `power10-vector`, `power8-altivec`, `power8-vector`, `power9-altivec`, `power9-vector`, `prfchw`, `quadword-atomics`, `rand`, `ras`, `rclass`, `rcpc`, `rcpc2`, `rcpc3`, `rdm`, `rdrand`, `rdseed`, `reference-types`, `relax`, `relaxed-simd`, `rtm`, `sb`, `sha`, `sha2`, `sha3`, `sha512`, `sign-ext`, `simd128`, `sm3`, `sm4`, `sme`, `sme-b16b16`, `sme-f16f16`, `sme-f64f64`, `sme-f8f16`, `sme-f8f32`, `sme-fa64`, `sme-i16i64`, `sme-lutv2`, `sme2`, `sme2p1`, `spe`, `ssbs`, `sse`, `sse2`, `sse3`, `sse4.1`, `sse4.2`, `sse4a`, `ssse3`, `ssve-fp8dot2`, `ssve-fp8dot4`, `ssve-fp8fma`, `sve`, `sve-b16b16`, `sve2`, `sve2-aes`, `sve2-bitperm`, `sve2-sha3`, `sve2-sm4`, `sve2p1`, `tail-call`, `tbm`, `thumb-mode`, `thumb2`, `tme`, `trust`, `trustzone`, `ual`, `unaligned-scalar-mem`, `v`, `v5te`, `v6`, `v6k`, `v6t2`, `v7`, `v8`, `v8.1a`, `v8.2a`, `v8.3a`, `v8.4a`, `v8.5a`, `v8.6a`, `v8.7a`, `v8.8a`, `v8.9a`, `v8plus`, `v9`, `v9.1a`, `v9.2a`, `v9.3a`, `v9.4a`, `v9.5a`, `v9a`, `vaes`, `vdsp2e60f`, `vdspv1`, `vdspv2`, `vector`, `vfp2`, `vfp3`, `vfp4`, `vh`, `virt`, `virtualization`, `vpclmulqdq`, `vsx`, `wfxt`, `wide-arithmetic`, `xop`, `xsave`, `xsavec`, `xsaveopt`, `xsaves`, `zaamo`, `zabha`, `zalrsc`, `zba`, `zbb`, `zbc`, `zbkb`, `zbkc`, `zbkx`, `zbs`, `zdinx`, `zfh`, `zfhmin`, `zfinx`, `zhinx`, `zhinxmin`, `zk`, `zkn`, `zknd`, `zkne`, `zknh`, `zkr`, `zks`, `zksed`, `zksh`, and `zkt`
+   = 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`, `avx512vpopcntdq`, `avxifma`, `avxneconvert`, `avxvnni`, `avxvnniint16`, `avxvnniint8`, `backchain`, `bf16`, `bmi1`, `bmi2`, `bti`, `bulk-memory`, `c`, `cache`, `cmpxchg16b`, `crc`, `crt-static`, `cssc`, `d`, `d32`, `dit`, `doloop`, `dotprod`, `dpb`, `dpb2`, `dsp`, `dsp1e2`, `dspe60`, `e`, `e1`, `e2`, `ecv`, `edsp`, `elrw`, `ermsb`, `exception-handling`, `extended-const`, `f`, `f16c`, `f32mm`, `f64mm`, `faminmax`, `fcma`, `fdivdu`, `fhm`, `flagm`, `flagm2`, `float1e2`, `float1e3`, `float3e4`, `float7e60`, `floate1`, `fma`, `fp-armv8`, `fp16`, `fp64`, `fp8`, `fp8dot2`, `fp8dot4`, `fp8fma`, `fpregs`, `fpuv2_df`, `fpuv2_sf`, `fpuv3_df`, `fpuv3_hf`, `fpuv3_hi`, `fpuv3_sf`, `frecipe`, `frintts`, `fxsr`, `gfni`, `hard-float`, `hard-float-abi`, `hard-tp`, `hbc`, `high-registers`, `hvx`, `hvx-length128b`, `hwdiv`, `i8mm`, `jsconv`, `lahfsahf`, `lasx`, `lbt`, `leoncasa`, `lor`, `lse`, `lse128`, `lse2`, `lsx`, `lut`, `lvz`, `lzcnt`, `m`, `mclass`, `mops`, `movbe`, `mp`, `mp1e2`, `msa`, `mte`, `multivalue`, `mutable-globals`, `neon`, `nontrapping-fptoint`, `nvic`, `paca`, `pacg`, `pan`, `partword-atomics`, `pauth-lr`, `pclmulqdq`, `pmuv3`, `popcnt`, `power10-vector`, `power8-altivec`, `power8-vector`, `power9-altivec`, `power9-vector`, `prfchw`, `quadword-atomics`, `rand`, `ras`, `rclass`, `rcpc`, `rcpc2`, `rcpc3`, `rdm`, `rdrand`, `rdseed`, `reference-types`, `relax`, `relaxed-simd`, `rtm`, `sb`, `sha`, `sha2`, `sha3`, `sha512`, `sign-ext`, `simd128`, `sm3`, `sm4`, `sme`, `sme-b16b16`, `sme-f16f16`, `sme-f64f64`, `sme-f8f16`, `sme-f8f32`, `sme-fa64`, `sme-i16i64`, `sme-lutv2`, `sme2`, `sme2p1`, `spe`, `ssbs`, `sse`, `sse2`, `sse3`, `sse4.1`, `sse4.2`, `sse4a`, `ssse3`, `ssve-fp8dot2`, `ssve-fp8dot4`, `ssve-fp8fma`, `sve`, `sve-b16b16`, `sve2`, `sve2-aes`, `sve2-bitperm`, `sve2-sha3`, `sve2-sm4`, `sve2p1`, `tail-call`, `tbm`, `thumb-mode`, `thumb2`, `tme`, `trust`, `trustzone`, `ual`, `unaligned-scalar-mem`, `v`, `v5te`, `v6`, `v6k`, `v6t2`, `v7`, `v8`, `v8.1a`, `v8.2a`, `v8.3a`, `v8.4a`, `v8.5a`, `v8.6a`, `v8.7a`, `v8.8a`, `v8.9a`, `v8plus`, `v9`, `v9.1a`, `v9.2a`, `v9.3a`, `v9.4a`, `v9.5a`, `v9a`, `vaes`, `vdsp2e60f`, `vdspv1`, `vdspv2`, `vector`, `vfp2`, `vfp3`, `vfp4`, `vh`, `virt`, `virtualization`, `vpclmulqdq`, `vsx`, `wfxt`, `wide-arithmetic`, `x87`, `xop`, `xsave`, `xsavec`, `xsaveopt`, `xsaves`, `zaamo`, `zabha`, `zalrsc`, `zba`, `zbb`, `zbc`, `zbkb`, `zbkc`, `zbkx`, `zbs`, `zdinx`, `zfh`, `zfhmin`, `zfinx`, `zhinx`, `zhinxmin`, `zk`, `zkn`, `zknd`, `zkne`, `zknh`, `zkr`, `zks`, `zksed`, `zksh`, and `zkt`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`

tests/ui/target-feature/allowed-softfloat-target-feature-attribute.rs

@@ -0,0 +1,11 @@
+//@ compile-flags: --target=x86_64-unknown-none --crate-type=lib
+//@ needs-llvm-components: x86
+//@ build-pass
+#![feature(no_core, lang_items, x87_target_feature)]
+#![no_core]
+
+#[lang = "sized"]
+pub trait Sized {}
+
+#[target_feature(enable = "x87")]
+pub unsafe fn my_fun() {}

tests/ui/target-feature/allowed-softfloat-target-feature-flag-disable.rs

@@ -0,0 +1,9 @@
+//@ compile-flags: --target=x86_64-unknown-none --crate-type=lib
+//@ needs-llvm-components: x86
+//@ compile-flags: -Ctarget-feature=-x87
+//@ build-pass
+#![feature(no_core, lang_items)]
+#![no_core]
+
+#[lang = "sized"]
+pub trait Sized {}

tests/ui/target-feature/allowed-softfloat-target-feature-flag-disable.stderr

@@ -0,0 +1,6 @@
+warning: unstable feature specified for `-Ctarget-feature`: `x87`
+   |
+   = note: this feature is not stably supported; its behavior can change in the future
+
+warning: 1 warning emitted
+

tests/ui/target-feature/forbidden-hardfloat-target-feature-attribute.rs

@@ -0,0 +1,11 @@
+//@ compile-flags: --target=x86_64-unknown-linux-gnu --crate-type=lib
+//@ needs-llvm-components: x86
+#![feature(no_core, lang_items)]
+#![no_core]
+
+#[lang = "sized"]
+pub trait Sized {}
+
+#[target_feature(enable = "x87")]
+//~^ERROR: cannot be toggled with
+pub unsafe fn my_fun() {}

tests/ui/target-feature/forbidden-hardfloat-target-feature-attribute.stderr

@@ -0,0 +1,8 @@
+error: target feature `x87` cannot be toggled with `#[target_feature]`: unsound on hard-float targets because it changes float ABI
+  --> $DIR/forbidden-hardfloat-target-feature-attribute.rs:9:18
+   |
+LL | #[target_feature(enable = "x87")]
+   |                  ^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+

tests/ui/target-feature/forbidden-hardfloat-target-feature-cfg.rs

@@ -0,0 +1,14 @@
+//@ compile-flags: --target=x86_64-unknown-linux-gnu --crate-type=lib
+//@ needs-llvm-components: x86
+//@ check-pass
+#![feature(no_core, lang_items)]
+#![no_core]
+#![allow(unexpected_cfgs)]
+
+#[lang = "sized"]
+pub trait Sized {}
+
+// The compile_error macro does not exist, so if the `cfg` evaluates to `true` this
+// complains about the missing macro rather than showing the error... but that's good enough.
+#[cfg(not(target_feature = "x87"))]
+compile_error!("the x87 feature *should* be exposed in `cfg`");

tests/ui/target-feature/forbidden-hardfloat-target-feature-flag-disable.rs

@@ -0,0 +1,10 @@
+//@ compile-flags: --target=x86_64-unknown-linux-gnu --crate-type=lib
+//@ needs-llvm-components: x86
+//@ compile-flags: -Ctarget-feature=-x87
+// For now this is just a warning.
+//@ build-pass
+#![feature(no_core, lang_items)]
+#![no_core]
+
+#[lang = "sized"]
+pub trait Sized {}

tests/ui/target-feature/forbidden-hardfloat-target-feature-flag-disable.stderr

@@ -0,0 +1,7 @@
+warning: target feature `x87` cannot be toggled with `-Ctarget-feature`: unsound on hard-float targets because it changes float ABI
+   |
+   = note: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #116344 <https://github.com/rust-lang/rust/issues/116344>
+
+warning: 1 warning emitted
+

tests/ui/target-feature/forbidden-target-feature-attribute.rs

@@ -1,7 +1,6 @@
 //@ compile-flags: --target=x86_64-unknown-linux-gnu --crate-type=lib
 //@ needs-llvm-components: x86
 #![feature(no_core, lang_items)]
-#![no_std]
 #![no_core]
 
 #[lang = "sized"]

tests/ui/target-feature/forbidden-target-feature-attribute.stderr

@@ -1,5 +1,5 @@
 error: target feature `soft-float` cannot be toggled with `#[target_feature]`: unsound because it changes float ABI
-  --> $DIR/forbidden-target-feature-attribute.rs:10:18
+  --> $DIR/forbidden-target-feature-attribute.rs:9:18
    |
 LL | #[target_feature(enable = "soft-float")]
    |                  ^^^^^^^^^^^^^^^^^^^^^

tests/ui/target-feature/forbidden-target-feature-cfg.rs

@@ -2,7 +2,6 @@
 //@ needs-llvm-components: x86
 //@ check-pass
 #![feature(no_core, lang_items)]
-#![no_std]
 #![no_core]
 #![allow(unexpected_cfgs)]
 

tests/ui/target-feature/forbidden-target-feature-flag-disable.rs

@@ -4,7 +4,6 @@
 // For now this is just a warning.
 //@ build-pass
 #![feature(no_core, lang_items)]
-#![no_std]
 #![no_core]
 
 #[lang = "sized"]

tests/ui/target-feature/forbidden-target-feature-flag.rs

@@ -4,7 +4,6 @@
 // For now this is just a warning.
 //@ build-pass
 #![feature(no_core, lang_items)]
-#![no_std]
 #![no_core]
 
 #[lang = "sized"]

tests/ui/target-feature/gate.rs

@@ -24,6 +24,7 @@
 // gate-test-prfchw_target_feature
 // gate-test-s390x_target_feature
 // gate-test-sparc_target_feature
+// gate-test-x87_target_feature
 
 #[target_feature(enable = "avx512bw")]
 //~^ ERROR: currently unstable

tests/ui/target-feature/gate.stderr

@@ -1,5 +1,5 @@
 error[E0658]: the target feature `avx512bw` is currently unstable
-  --> $DIR/gate.rs:28:18
+  --> $DIR/gate.rs:29:18
    |
 LL | #[target_feature(enable = "avx512bw")]
    |                  ^^^^^^^^^^^^^^^^^^^