Auto merge of #136146 - RalfJung:x86-abi, r=workingjubilee

Explicitly choose x86 softfloat/hardfloat ABI

Part of #135408:
Instead of choosing this based on the target features listed in the target spec, make that choice explicit.
This means that all x86 (32bit and 64bit) softfloat target need to explicitly set `rustc-abi` to `x86-softfloat`.

Also fix some mistakes in the platform-docs where the x87 errata footnotes were missing or wrong.

try-job: x86_64-rust-for-linux

compiler/rustc_target/src/spec/json.rs

@@ -128,6 +128,19 @@ impl Target {
                     Some(Ok(()))
                 })).unwrap_or(Ok(()))
             } );
+            ($key_name:ident, RustcAbi) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
+                    match s.parse::<super::RustcAbi>() {
+                        Ok(rustc_abi) => base.$key_name = Some(rustc_abi),
+                        _ => return Some(Err(format!(
+                            "'{s}' is not a valid value for rustc-abi. \
+                            Use 'x86-softfloat' or leave the field unset."
+                        ))),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
             ($key_name:ident, RelocModel) => ( {
                 let name = (stringify!($key_name)).replace("_", "-");
                 obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
@@ -612,6 +625,7 @@ impl Target {
         key!(llvm_mcount_intrinsic, optional);
         key!(llvm_abiname);
         key!(llvm_floatabi, FloatAbi)?;
+        key!(rustc_abi, RustcAbi)?;
         key!(relax_elf_relocations, bool);
         key!(llvm_args, list);
         key!(use_ctors_section, bool);
@@ -788,6 +802,7 @@ impl ToJson for Target {
         target_option_val!(llvm_mcount_intrinsic);
         target_option_val!(llvm_abiname);
         target_option_val!(llvm_floatabi);
+        target_option_val!(rustc_abi);
         target_option_val!(relax_elf_relocations);
         target_option_val!(llvm_args);
         target_option_val!(use_ctors_section);

compiler/rustc_target/src/spec/mod.rs

@@ -1114,6 +1114,33 @@ impl ToJson for FloatAbi {
     }
 }
 
+/// The Rustc-specific variant of the ABI used for this target.
+#[derive(Clone, Copy, PartialEq, Hash, Debug)]
+pub enum RustcAbi {
+    /// On x86-32/64 only: do not use any FPU or SIMD registers for the ABI.
+    X86Softfloat,
+}
+
+impl FromStr for RustcAbi {
+    type Err = ();
+
+    fn from_str(s: &str) -> Result<RustcAbi, ()> {
+        Ok(match s {
+            "x86-softfloat" => RustcAbi::X86Softfloat,
+            _ => return Err(()),
+        })
+    }
+}
+
+impl ToJson for RustcAbi {
+    fn to_json(&self) -> Json {
+        match *self {
+            RustcAbi::X86Softfloat => "x86-softfloat",
+        }
+        .to_json()
+    }
+}
+
 #[derive(Clone, Copy, PartialEq, Hash, Debug)]
 pub enum TlsModel {
     GeneralDynamic,
@@ -2505,6 +2532,12 @@ pub struct TargetOptions {
     /// If not provided, LLVM will infer the float ABI from the target triple (`llvm_target`).
     pub llvm_floatabi: Option<FloatAbi>,
 
+    /// Picks a specific ABI for this target. This is *not* just for "Rust" ABI functions,
+    /// it can also affect "C" ABI functions; the point is that this flag is interpreted by
+    /// rustc and not forwarded to LLVM.
+    /// So far, this is only used on x86.
+    pub rustc_abi: Option<RustcAbi>,
+
     /// Whether or not RelaxElfRelocation flag will be passed to the linker
     pub relax_elf_relocations: bool,
 
@@ -2664,10 +2697,6 @@ impl TargetOptions {
                 .collect();
         }
     }
-
-    pub(crate) fn has_feature(&self, search_feature: &str) -> bool {
-        self.features.split(',').any(|f| f.strip_prefix('+').is_some_and(|f| f == search_feature))
-    }
 }
 
 impl Default for TargetOptions {
@@ -2774,6 +2803,7 @@ impl Default for TargetOptions {
             llvm_mcount_intrinsic: None,
             llvm_abiname: "".into(),
             llvm_floatabi: None,
+            rustc_abi: None,
             relax_elf_relocations: false,
             llvm_args: cvs![],
             use_ctors_section: false,
@@ -3240,6 +3270,17 @@ impl Target {
             _ => {}
         }
 
+        // Check consistency of Rust ABI declaration.
+        if let Some(rust_abi) = self.rustc_abi {
+            match rust_abi {
+                RustcAbi::X86Softfloat => check_matches!(
+                    &*self.arch,
+                    "x86" | "x86_64",
+                    "`x86-softfloat` ABI is only valid for x86 targets"
+                ),
+            }
+        }
+
         // Check that the given target-features string makes some basic sense.
         if !self.features.is_empty() {
             let mut features_enabled = FxHashSet::default();

compiler/rustc_target/src/spec/targets/i686_unknown_uefi.rs

@@ -5,7 +5,7 @@
 // The cdecl ABI is used. It differs from the stdcall or fastcall ABI.
 // "i686-unknown-windows" is used to get the minimal subset of windows-specific features.
 
-use crate::spec::{Target, base};
+use crate::spec::{RustcAbi, Target, base};
 
 pub(crate) fn target() -> Target {
     let mut base = base::uefi_msvc::opts();
@@ -22,6 +22,7 @@ pub(crate) fn target() -> Target {
     // If you initialize FP units yourself, you can override these flags with custom linker
     // arguments, thus giving you access to full MMX/SSE acceleration.
     base.features = "-mmx,-sse,+soft-float".into();
+    base.rustc_abi = Some(RustcAbi::X86Softfloat);
 
     // Use -GNU here, because of the reason below:
     // Background and Problem:

compiler/rustc_target/src/spec/targets/x86_64_unknown_none.rs

@@ -5,8 +5,8 @@
 // features.
 
 use crate::spec::{
-    Cc, CodeModel, LinkerFlavor, Lld, PanicStrategy, RelroLevel, SanitizerSet, StackProbeType,
-    Target, TargetOptions,
+    Cc, CodeModel, LinkerFlavor, Lld, PanicStrategy, RelroLevel, RustcAbi, SanitizerSet,
+    StackProbeType, Target, TargetOptions,
 };
 
 pub(crate) fn target() -> Target {
@@ -20,6 +20,7 @@ pub(crate) fn target() -> Target {
         relro_level: RelroLevel::Full,
         linker_flavor: LinkerFlavor::Gnu(Cc::No, Lld::Yes),
         linker: Some("rust-lld".into()),
+        rustc_abi: Some(RustcAbi::X86Softfloat),
         features: "-mmx,-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2,+soft-float".into(),
         supported_sanitizers: SanitizerSet::KCFI | SanitizerSet::KERNELADDRESS,
         disable_redzone: true,

compiler/rustc_target/src/spec/targets/x86_64_unknown_uefi.rs

@@ -6,7 +6,7 @@
 // LLVM. "x86_64-unknown-windows" is used to get the minimal subset of windows-specific features.
 
 use crate::abi::call::Conv;
-use crate::spec::{Target, base};
+use crate::spec::{RustcAbi, Target, base};
 
 pub(crate) fn target() -> Target {
     let mut base = base::uefi_msvc::opts();
@@ -26,6 +26,7 @@ pub(crate) fn target() -> Target {
     // If you initialize FP units yourself, you can override these flags with custom linker
     // arguments, thus giving you access to full MMX/SSE acceleration.
     base.features = "-mmx,-sse,+soft-float".into();
+    base.rustc_abi = Some(RustcAbi::X86Softfloat);
 
     Target {
         llvm_target: "x86_64-unknown-windows".into(),

compiler/rustc_target/src/target_features.rs

@@ -5,7 +5,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_span::{Symbol, sym};
 
-use crate::spec::{FloatAbi, Target};
+use crate::spec::{FloatAbi, RustcAbi, Target};
 
 /// Features that control behaviour of rustc, rather than the codegen.
 /// These exist globally and are not in the target-specific lists below.
@@ -422,7 +422,9 @@ const X86_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     ("sha512", Unstable(sym::sha512_sm_x86), &["avx2"]),
     ("sm3", Unstable(sym::sha512_sm_x86), &["avx"]),
     ("sm4", Unstable(sym::sha512_sm_x86), &["avx2"]),
-    ("soft-float", Stability::Forbidden { reason: "unsound because it changes float ABI" }, &[]),
+    // This cannot actually be toggled, the ABI always fixes it, so it'd make little sense to
+    // stabilize. It must be in this list for the ABI check to be able to use it.
+    ("soft-float", Stability::Unstable(sym::x87_target_feature), &[]),
     ("sse", Stable, &[]),
     ("sse2", Stable, &["sse"]),
     ("sse3", Stable, &["sse2"]),
@@ -773,23 +775,41 @@ impl Target {
         // questions "which ABI is used".
         match &*self.arch {
             "x86" => {
-                // We support 2 ABIs, hardfloat (default) and softfloat.
-                // x86 has no sane ABI indicator so we have to use the target feature.
-                if self.has_feature("soft-float") {
-                    NOTHING
-                } else {
-                    // Hardfloat ABI. x87 must be enabled.
-                    FeatureConstraints { required: &["x87"], incompatible: &[] }
+                // We use our own ABI indicator here; LLVM does not have anything native.
+                // Every case should require or forbid `soft-float`!
+                match self.rustc_abi {
+                    None => {
+                        // Default hardfloat ABI.
+                        // x87 must be enabled, soft-float must be disabled.
+                        FeatureConstraints { required: &["x87"], incompatible: &["soft-float"] }
+                    }
+                    Some(RustcAbi::X86Softfloat) => {
+                        // Softfloat ABI, requires corresponding target feature. That feature trumps
+                        // `x87` and all other FPU features so those do not matter.
+                        // Note that this one requirement is the entire implementation of the ABI!
+                        // LLVM handles the rest.
+                        FeatureConstraints { required: &["soft-float"], incompatible: &[] }
+                    }
                 }
             }
             "x86_64" => {
-                // We support 2 ABIs, hardfloat (default) and softfloat.
-                // x86 has no sane ABI indicator so we have to use the target feature.
-                if self.has_feature("soft-float") {
-                    NOTHING
-                } else {
-                    // Hardfloat ABI. x87 and SSE2 must be enabled.
-                    FeatureConstraints { required: &["x87", "sse2"], incompatible: &[] }
+                // We use our own ABI indicator here; LLVM does not have anything native.
+                // Every case should require or forbid `soft-float`!
+                match self.rustc_abi {
+                    None => {
+                        // Default hardfloat ABI. On x86-64, this always includes SSE2.
+                        FeatureConstraints {
+                            required: &["x87", "sse2"],
+                            incompatible: &["soft-float"],
+                        }
+                    }
+                    Some(RustcAbi::X86Softfloat) => {
+                        // Softfloat ABI, requires corresponding target feature. That feature trumps
+                        // `x87` and all other FPU features so those do not matter.
+                        // Note that this one requirement is the entire implementation of the ABI!
+                        // LLVM handles the rest.
+                        FeatureConstraints { required: &["soft-float"], incompatible: &[] }
+                    }
                 }
             }
             "arm" => {

src/ci/docker/scripts/rfl-build.sh

@@ -2,7 +2,7 @@
 
 set -euo pipefail
 
-LINUX_VERSION=v6.13-rc1
+LINUX_VERSION=5c4c930873e33cff6d1db9cae56a6cc321fde1af
 
 # Build rustc, rustdoc, cargo, clippy-driver and rustfmt
 ../x.py build --stage 2 library rustdoc clippy rustfmt
@@ -28,7 +28,7 @@ rm -rf linux || true
 # Download Linux at a specific commit
 mkdir -p linux
 git -C linux init
-git -C linux remote add origin https://github.com/Rust-for-Linux/linux.git
+git -C linux remote add origin https://github.com/Darksonn/linux.git
 git -C linux fetch --depth 1 origin ${LINUX_VERSION}
 git -C linux checkout FETCH_HEAD
 

src/doc/rustc/src/platform-support.md

@@ -309,13 +309,13 @@ target | std | host | notes
 [`hexagon-unknown-none-elf`](platform-support/hexagon-unknown-none-elf.md)| * | | Bare Hexagon (v60+, HVX)
 [`i386-apple-ios`](platform-support/apple-ios.md) | ✓ |  | 32-bit x86 iOS [^x86_32-floats-return-ABI]
 [`i586-pc-nto-qnx700`](platform-support/nto-qnx.md) | * |  | 32-bit x86 QNX Neutrino 7.0 RTOS  [^x86_32-floats-return-ABI]
-[`i586-unknown-netbsd`](platform-support/netbsd.md) | ✓ |  | 32-bit x86, restricted to Pentium
+[`i586-unknown-netbsd`](platform-support/netbsd.md) | ✓ |  | 32-bit x86, restricted to Pentium [^x86_32-floats-x87]
 [`i686-apple-darwin`](platform-support/apple-darwin.md) | ✓ | ✓ | 32-bit macOS (10.12+, Sierra+) [^x86_32-floats-return-ABI]
-`i686-unknown-haiku` | ✓ | ✓ | 32-bit Haiku [^x86_32-floats-return-ABI]
-[`i686-unknown-hurd-gnu`](platform-support/hurd.md) | ✓ | ✓ | 32-bit GNU/Hurd [^x86_32-floats-return-ABI]
+`i686-unknown-haiku` | ✓ | ✓ | 32-bit Haiku with SSE [^x86_32-floats-return-ABI]
+[`i686-unknown-hurd-gnu`](platform-support/hurd.md) | ✓ | ✓ | 32-bit GNU/Hurd w/o SSE [^x86_32-floats-x87]
 [`i686-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | NetBSD/i386 with SSE2 [^x86_32-floats-return-ABI]
-[`i686-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 32-bit OpenBSD [^x86_32-floats-return-ABI]
-[`i686-unknown-redox`](platform-support/redox.md) | ✓ |  | i686 Redox OS
+[`i686-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 32-bit OpenBSD with SSE2 [^x86_32-floats-return-ABI]
+[`i686-unknown-redox`](platform-support/redox.md) | ✓ |  | i686 Redox OS w/o SSE [^x86_32-floats-x87]
 `i686-uwp-windows-gnu` | ✓ |  | [^x86_32-floats-return-ABI]
 [`i686-uwp-windows-msvc`](platform-support/uwp-windows-msvc.md) | ✓ |  | [^x86_32-floats-return-ABI]
 [`i686-win7-windows-gnu`](platform-support/win7-windows-gnu.md) | ✓ |   | 32-bit Windows 7 support [^x86_32-floats-return-ABI]

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

@@ -1,3 +1,4 @@
+//! Ensure ABI-incompatible features cannot be enabled via `#[target_feature]`.
 //@ compile-flags: --target=riscv32e-unknown-none-elf --crate-type=lib
 //@ needs-llvm-components: riscv
 #![feature(no_core, lang_items, riscv_target_feature)]

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

@@ -1,5 +1,5 @@
 error: target feature `d` cannot be enabled with `#[target_feature]`: this feature is incompatible with the target ABI
-  --> $DIR/forbidden-hardfloat-target-feature-attribute.rs:9:18
+  --> $DIR/forbidden-hardfloat-target-feature-attribute.rs:10:18
    |
 LL | #[target_feature(enable = "d")]
    |                  ^^^^^^^^^^^^

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

@@ -1,8 +1,11 @@
+//! Ensure that if disabling a target feature implies disabling an ABI-required target feature,
+//! we complain.
 //@ compile-flags: --target=x86_64-unknown-linux-gnu --crate-type=lib
 //@ needs-llvm-components: x86
 //@ compile-flags: -Ctarget-feature=-sse
 // For now this is just a warning.
 //@ build-pass
+//@error-pattern: must be enabled to ensure that the ABI
 #![feature(no_core, lang_items)]
 #![no_core]
 

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

@@ -3,6 +3,7 @@
 //@ compile-flags: -Ctarget-feature=-neon
 // For now this is just a warning.
 //@ build-pass
+//@error-pattern: must be enabled to ensure that the ABI
 #![feature(no_core, lang_items)]
 #![no_core]
 

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

@@ -1,8 +1,10 @@
+//! Ensure ABI-required features cannot be disabled via `-Ctarget-feature`.
 //@ 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
+//@error-pattern: must be enabled to ensure that the ABI
 #![feature(no_core, lang_items)]
 #![no_core]
 

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

@@ -0,0 +1,12 @@
+//! Ensure ABI-incompatible features cannot be enabled via `-Ctarget-feature`.
+//@ compile-flags: --target=x86_64-unknown-linux-gnu --crate-type=lib
+//@ needs-llvm-components: x86
+//@ compile-flags: -Ctarget-feature=+soft-float
+// For now this is just a warning.
+//@ build-pass
+//@error-pattern: must be disabled to ensure that the ABI
+#![feature(no_core, lang_items, riscv_target_feature)]
+#![no_core]
+
+#[lang = "sized"]
+pub trait Sized {}

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

@@ -0,0 +1,11 @@
+warning: target feature `soft-float` must be disabled to ensure that the ABI of the current target can be implemented correctly
+   |
+   = 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: unstable feature specified for `-Ctarget-feature`: `soft-float`
+   |
+   = note: this feature is not stably supported; its behavior can change in the future
+
+warning: 2 warnings emitted
+

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

@@ -1,11 +1,12 @@
-//@ compile-flags: --target=x86_64-unknown-linux-gnu --crate-type=lib
-//@ needs-llvm-components: x86
+//! Ensure "forbidden" target features cannot be enabled via `#[target_feature]`.
+//@ compile-flags: --target=riscv32e-unknown-none-elf --crate-type=lib
+//@ needs-llvm-components: riscv
 #![feature(no_core, lang_items)]
 #![no_core]
 
 #[lang = "sized"]
 pub trait Sized {}
 
-#[target_feature(enable = "soft-float")]
+#[target_feature(enable = "forced-atomics")]
 //~^ERROR: cannot be enabled with
 pub unsafe fn my_fun() {}

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

@@ -1,8 +1,8 @@
-error: target feature `soft-float` cannot be enabled with `#[target_feature]`: unsound because it changes float ABI
-  --> $DIR/forbidden-target-feature-attribute.rs:9:18
+error: target feature `forced-atomics` cannot be enabled with `#[target_feature]`: unsound because it changes the ABI of atomic operations
+  --> $DIR/forbidden-target-feature-attribute.rs:10:18
    |
-LL | #[target_feature(enable = "soft-float")]
-   |                  ^^^^^^^^^^^^^^^^^^^^^
+LL | #[target_feature(enable = "forced-atomics")]
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error