Auto merge of #117919 - daxpedda:wasm-c-abi, r=wesleywiser

Introduce perma-unstable `wasm-c-abi` flag

Now that `wasm-bindgen` v0.2.88 supports the spec-compliant C ABI, the idea is to switch to that in a future version of Rust. In the meantime it would be good to let people test and play around with it.

This PR introduces a new perma-unstable `-Zwasm-c-abi` compiler flag, which switches to the new spec-compliant C ABI when targeting `wasm32-unknown-unknown`.

Alternatively, we could also stabilize this and then deprecate it when we switch. I will leave this to the Rust maintainers to decide.

This is a companion PR to #117918, but they could be merged independently.
MCP: https://github.com/rust-lang/compiler-team/issues/703
Tracking issue: https://github.com/rust-lang/rust/issues/122532

compiler/rustc_codegen_gcc/src/builder.rs

@@ -31,7 +31,7 @@ use rustc_span::Span;
 use rustc_target::abi::{
     self, call::FnAbi, Align, HasDataLayout, Size, TargetDataLayout, WrappingRange,
 };
-use rustc_target::spec::{HasTargetSpec, Target};
+use rustc_target::spec::{HasTargetSpec, HasWasmCAbiOpt, Target, WasmCAbi};
 
 use crate::common::{type_is_pointer, SignType, TypeReflection};
 use crate::context::CodegenCx;
@@ -2352,6 +2352,12 @@ impl<'tcx> HasTargetSpec for Builder<'_, '_, 'tcx> {
     }
 }
 
+impl<'tcx> HasWasmCAbiOpt for Builder<'_, '_, 'tcx> {
+    fn wasm_c_abi_opt(&self) -> WasmCAbi {
+        self.cx.wasm_c_abi_opt()
+    }
+}
+
 pub trait ToGccComp {
     fn to_gcc_comparison(&self) -> ComparisonOp;
 }

compiler/rustc_codegen_gcc/src/context.rs

@@ -20,7 +20,7 @@ use rustc_span::{source_map::respan, Span};
 use rustc_target::abi::{
     call::FnAbi, HasDataLayout, PointeeInfo, Size, TargetDataLayout, VariantIdx,
 };
-use rustc_target::spec::{HasTargetSpec, Target, TlsModel};
+use rustc_target::spec::{HasTargetSpec, HasWasmCAbiOpt, Target, TlsModel, WasmCAbi};
 
 use crate::callee::get_fn;
 use crate::common::SignType;
@@ -557,6 +557,12 @@ impl<'gcc, 'tcx> HasTargetSpec for CodegenCx<'gcc, 'tcx> {
     }
 }
 
+impl<'gcc, 'tcx> HasWasmCAbiOpt for CodegenCx<'gcc, 'tcx> {
+    fn wasm_c_abi_opt(&self) -> WasmCAbi {
+        self.tcx.sess.opts.unstable_opts.wasm_c_abi
+    }
+}
+
 impl<'gcc, 'tcx> LayoutOfHelpers<'tcx> for CodegenCx<'gcc, 'tcx> {
     type LayoutOfResult = TyAndLayout<'tcx>;
 

compiler/rustc_interface/src/tests.rs

@@ -19,7 +19,9 @@ use rustc_span::edition::{Edition, DEFAULT_EDITION};
 use rustc_span::source_map::{RealFileLoader, SourceMapInputs};
 use rustc_span::symbol::sym;
 use rustc_span::{FileName, SourceFileHashAlgorithm};
-use rustc_target::spec::{CodeModel, LinkerFlavorCli, MergeFunctions, PanicStrategy, RelocModel};
+use rustc_target::spec::{
+    CodeModel, LinkerFlavorCli, MergeFunctions, PanicStrategy, RelocModel, WasmCAbi,
+};
 use rustc_target::spec::{RelroLevel, SanitizerSet, SplitDebuginfo, StackProtector, TlsModel};
 use std::collections::{BTreeMap, BTreeSet};
 use std::num::NonZero;
@@ -851,6 +853,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(verify_llvm_ir, true);
     tracked!(virtual_function_elimination, true);
     tracked!(wasi_exec_model, Some(WasiExecModel::Reactor));
+    tracked!(wasm_c_abi, WasmCAbi::Spec);
     // tidy-alphabetical-end
 
     macro_rules! tracked_no_crate_hash {

compiler/rustc_middle/src/ty/layout.rs

@@ -15,7 +15,9 @@ use rustc_span::symbol::{sym, Symbol};
 use rustc_span::{ErrorGuaranteed, Span, DUMMY_SP};
 use rustc_target::abi::call::FnAbi;
 use rustc_target::abi::*;
-use rustc_target::spec::{abi::Abi as SpecAbi, HasTargetSpec, PanicStrategy, Target};
+use rustc_target::spec::{
+    abi::Abi as SpecAbi, HasTargetSpec, HasWasmCAbiOpt, PanicStrategy, Target, WasmCAbi,
+};
 
 use std::borrow::Cow;
 use std::cmp;
@@ -483,6 +485,12 @@ impl<'tcx> HasTargetSpec for TyCtxt<'tcx> {
     }
 }
 
+impl<'tcx> HasWasmCAbiOpt for TyCtxt<'tcx> {
+    fn wasm_c_abi_opt(&self) -> WasmCAbi {
+        self.sess.opts.unstable_opts.wasm_c_abi
+    }
+}
+
 impl<'tcx> HasTyCtxt<'tcx> for TyCtxt<'tcx> {
     #[inline]
     fn tcx(&self) -> TyCtxt<'tcx> {
@@ -528,6 +536,12 @@ impl<'tcx, T: HasTargetSpec> HasTargetSpec for LayoutCx<'tcx, T> {
     }
 }
 
+impl<'tcx, T: HasWasmCAbiOpt> HasWasmCAbiOpt for LayoutCx<'tcx, T> {
+    fn wasm_c_abi_opt(&self) -> WasmCAbi {
+        self.tcx.wasm_c_abi_opt()
+    }
+}
+
 impl<'tcx, T: HasTyCtxt<'tcx>> HasTyCtxt<'tcx> for LayoutCx<'tcx, T> {
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx.tcx()

compiler/rustc_session/src/config.rs

@@ -2880,7 +2880,7 @@ pub(crate) mod dep_tracking {
     use rustc_feature::UnstableFeatures;
     use rustc_span::edition::Edition;
     use rustc_span::RealFileName;
-    use rustc_target::spec::{CodeModel, MergeFunctions, PanicStrategy, RelocModel};
+    use rustc_target::spec::{CodeModel, MergeFunctions, PanicStrategy, RelocModel, WasmCAbi};
     use rustc_target::spec::{
         RelroLevel, SanitizerSet, SplitDebuginfo, StackProtector, TargetTriple, TlsModel,
     };
@@ -2978,6 +2978,7 @@ pub(crate) mod dep_tracking {
         Polonius,
         InliningThreshold,
         FunctionReturn,
+        WasmCAbi,
     );
 
     impl<T1, T2> DepTrackingHash for (T1, T2)

compiler/rustc_session/src/options.rs

@@ -8,7 +8,9 @@ use rustc_data_structures::profiling::TimePassesFormat;
 use rustc_data_structures::stable_hasher::Hash64;
 use rustc_errors::ColorConfig;
 use rustc_errors::{LanguageIdentifier, TerminalUrl};
-use rustc_target::spec::{CodeModel, LinkerFlavorCli, MergeFunctions, PanicStrategy, SanitizerSet};
+use rustc_target::spec::{
+    CodeModel, LinkerFlavorCli, MergeFunctions, PanicStrategy, SanitizerSet, WasmCAbi,
+};
 use rustc_target::spec::{
     RelocModel, RelroLevel, SplitDebuginfo, StackProtector, TargetTriple, TlsModel,
 };
@@ -441,6 +443,7 @@ mod desc {
         "either a boolean (`yes`, `no`, `on`, `off`, etc), or a non-negative number";
     pub const parse_llvm_module_flag: &str = "<key>:<type>:<value>:<behavior>. Type must currently be `u32`. Behavior should be one of (`error`, `warning`, `require`, `override`, `append`, `appendunique`, `max`, `min`)";
     pub const parse_function_return: &str = "`keep` or `thunk-extern`";
+    pub const parse_wasm_c_abi: &str = "`legacy` or `spec`";
 }
 
 mod parse {
@@ -1433,6 +1436,15 @@ mod parse {
         }
         true
     }
+
+    pub(crate) fn parse_wasm_c_abi(slot: &mut WasmCAbi, v: Option<&str>) -> bool {
+        match v {
+            Some("spec") => *slot = WasmCAbi::Spec,
+            Some("legacy") => *slot = WasmCAbi::Legacy,
+            _ => return false,
+        }
+        true
+    }
 }
 
 options! {
@@ -2061,6 +2073,8 @@ written to standard error output)"),
         Requires `-Clto[=[fat,yes]]`"),
     wasi_exec_model: Option<WasiExecModel> = (None, parse_wasi_exec_model, [TRACKED],
         "whether to build a wasi command or reactor"),
+    wasm_c_abi: WasmCAbi = (WasmCAbi::Legacy, parse_wasm_c_abi, [TRACKED],
+        "use spec-compliant C ABI for `wasm32-unknown-unknown` (default: legacy)"),
     write_long_types_to_disk: bool = (true, parse_bool, [UNTRACKED],
         "whether long type names should be written to files instead of being printed in errors"),
     // tidy-alphabetical-end

compiler/rustc_target/src/abi/call/mod.rs

@@ -1,6 +1,6 @@
 use crate::abi::{self, Abi, Align, FieldsShape, Size};
 use crate::abi::{HasDataLayout, TyAbiInterface, TyAndLayout};
-use crate::spec::{self, HasTargetSpec};
+use crate::spec::{self, HasTargetSpec, HasWasmCAbiOpt};
 use rustc_span::Symbol;
 use std::fmt;
 use std::str::FromStr;
@@ -829,7 +829,7 @@ impl<'a, Ty> FnAbi<'a, Ty> {
     ) -> Result<(), AdjustForForeignAbiError>
     where
         Ty: TyAbiInterface<'a, C> + Copy,
-        C: HasDataLayout + HasTargetSpec,
+        C: HasDataLayout + HasTargetSpec + HasWasmCAbiOpt,
     {
         if abi == spec::abi::Abi::X86Interrupt {
             if let Some(arg) = self.args.first_mut() {
@@ -886,7 +886,9 @@ impl<'a, Ty> FnAbi<'a, Ty> {
             "sparc" => sparc::compute_abi_info(cx, self),
             "sparc64" => sparc64::compute_abi_info(cx, self),
             "nvptx64" => {
-                if cx.target_spec().adjust_abi(abi, self.c_variadic) == spec::abi::Abi::PtxKernel {
+                if cx.target_spec().adjust_abi(cx, abi, self.c_variadic)
+                    == spec::abi::Abi::PtxKernel
+                {
                     nvptx64::compute_ptx_kernel_abi_info(cx, self)
                 } else {
                     nvptx64::compute_abi_info(self)
@@ -895,7 +897,7 @@ impl<'a, Ty> FnAbi<'a, Ty> {
             "hexagon" => hexagon::compute_abi_info(self),
             "riscv32" | "riscv64" => riscv::compute_abi_info(cx, self),
             "wasm32" | "wasm64" => {
-                if cx.target_spec().adjust_abi(abi, self.c_variadic) == spec::abi::Abi::Wasm {
+                if cx.target_spec().adjust_abi(cx, abi, self.c_variadic) == spec::abi::Abi::Wasm {
                     wasm::compute_wasm_abi_info(self)
                 } else {
                     wasm::compute_c_abi_info(cx, self)

compiler/rustc_target/src/spec/mod.rs

@@ -37,7 +37,7 @@
 use crate::abi::call::Conv;
 use crate::abi::{Endian, Integer, Size, TargetDataLayout, TargetDataLayoutErrors};
 use crate::json::{Json, ToJson};
-use crate::spec::abi::{lookup as lookup_abi, Abi};
+use crate::spec::abi::Abi;
 use crate::spec::crt_objects::CrtObjects;
 use rustc_fs_util::try_canonicalize;
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
@@ -1915,6 +1915,19 @@ impl HasTargetSpec for Target {
     }
 }
 
+/// Which C ABI to use for `wasm32-unknown-unknown`.
+#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
+pub enum WasmCAbi {
+    /// Spec-compliant C ABI.
+    Spec,
+    /// Legacy ABI. Which is non-spec-compliant.
+    Legacy,
+}
+
+pub trait HasWasmCAbiOpt {
+    fn wasm_c_abi_opt(&self) -> WasmCAbi;
+}
+
 type StaticCow<T> = Cow<'static, T>;
 
 /// Optional aspects of a target specification.
@@ -2273,9 +2286,6 @@ pub struct TargetOptions {
     /// distributed with the target, the sanitizer should still appear in this list for the target.
     pub supported_sanitizers: SanitizerSet,
 
-    /// If present it's a default value to use for adjusting the C ABI.
-    pub default_adjusted_cabi: Option<Abi>,
-
     /// Minimum number of bits in #[repr(C)] enum. Defaults to the size of c_int
     pub c_enum_min_bits: Option<u64>,
 
@@ -2507,7 +2517,6 @@ impl Default for TargetOptions {
             // `Off` is supported by default, but targets can remove this manually, e.g. Windows.
             supported_split_debuginfo: Cow::Borrowed(&[SplitDebuginfo::Off]),
             supported_sanitizers: SanitizerSet::empty(),
-            default_adjusted_cabi: None,
             c_enum_min_bits: None,
             generate_arange_section: true,
             supports_stack_protector: true,
@@ -2538,9 +2547,21 @@ impl DerefMut for Target {
 
 impl Target {
     /// Given a function ABI, turn it into the correct ABI for this target.
-    pub fn adjust_abi(&self, abi: Abi, c_variadic: bool) -> Abi {
+    pub fn adjust_abi<C>(&self, cx: &C, abi: Abi, c_variadic: bool) -> Abi
+    where
+        C: HasWasmCAbiOpt,
+    {
         match abi {
-            Abi::C { .. } => self.default_adjusted_cabi.unwrap_or(abi),
+            Abi::C { .. } => {
+                if self.arch == "wasm32"
+                    && self.os == "unknown"
+                    && cx.wasm_c_abi_opt() == WasmCAbi::Legacy
+                {
+                    Abi::Wasm
+                } else {
+                    abi
+                }
+            }
 
             // On Windows, `extern "system"` behaves like msvc's `__stdcall`.
             // `__stdcall` only applies on x86 and on non-variadic functions:
@@ -3079,16 +3100,6 @@ impl Target {
                     }
                 }
             } );
-            ($key_name:ident, Option<Abi>) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
-                    match lookup_abi(s) {
-                        Ok(abi) => base.$key_name = Some(abi),
-                        _ => return Some(Err(format!("'{}' is not a valid value for abi", s))),
-                    }
-                    Some(Ok(()))
-                })).unwrap_or(Ok(()))
-            } );
             ($key_name:ident, TargetFamilies) => ( {
                 if let Some(value) = obj.remove("target-family") {
                     if let Some(v) = value.as_array() {
@@ -3238,7 +3249,6 @@ impl Target {
         key!(split_debuginfo, SplitDebuginfo)?;
         key!(supported_split_debuginfo, fallible_list)?;
         key!(supported_sanitizers, SanitizerSet)?;
-        key!(default_adjusted_cabi, Option<Abi>)?;
         key!(generate_arange_section, bool);
         key!(supports_stack_protector, bool);
         key!(entry_name);
@@ -3502,10 +3512,6 @@ impl ToJson for Target {
         target_option_val!(entry_abi);
         target_option_val!(supports_xray);
 
-        if let Some(abi) = self.default_adjusted_cabi {
-            d.insert("default-adjusted-cabi".into(), Abi::name(abi).to_json());
-        }
-
         // Serializing `-Clink-self-contained` needs a dynamic key to support the
         // backwards-compatible variants.
         d.insert(self.link_self_contained.json_key().into(), self.link_self_contained.to_json());

compiler/rustc_target/src/spec/targets/wasm32_unknown_unknown.rs

@@ -10,23 +10,12 @@
 //! This target is more or less managed by the Rust and WebAssembly Working
 //! Group nowadays at <https://github.com/rustwasm>.
 
-use crate::spec::abi::Abi;
 use crate::spec::{base, Cc, LinkerFlavor, Target};
 
 pub fn target() -> Target {
     let mut options = base::wasm::options();
     options.os = "unknown".into();
 
-    // This is a default for backwards-compatibility with the original
-    // definition of this target oh-so-long-ago. Once the "wasm" ABI is
-    // stable and the wasm-bindgen project has switched to using it then there's
-    // no need for this and it can be removed.
-    //
-    // Currently this is the reason that this target's ABI is mismatched with
-    // clang's ABI. This means that, in the limit, you can't merge C and Rust
-    // code on this target due to this ABI mismatch.
-    options.default_adjusted_cabi = Some(Abi::Wasm);
-
     options.add_pre_link_args(
         LinkerFlavor::WasmLld(Cc::No),
         &[

compiler/rustc_ty_utils/src/abi.rs

@@ -322,7 +322,7 @@ fn fn_sig_for_fn_abi<'tcx>(
 #[inline]
 fn conv_from_spec_abi(tcx: TyCtxt<'_>, abi: SpecAbi, c_variadic: bool) -> Conv {
     use rustc_target::spec::abi::Abi::*;
-    match tcx.sess.target.adjust_abi(abi, c_variadic) {
+    match tcx.sess.target.adjust_abi(&tcx, abi, c_variadic) {
         RustIntrinsic | Rust | RustCall => Conv::Rust,
 
         // This is intentionally not using `Conv::Cold`, as that has to preserve

src/doc/unstable-book/src/compiler-flags/wasm-c-abi.md

@@ -0,0 +1,10 @@
+# `wasm-c-abi`
+
+This option controls whether Rust uses the spec-compliant C ABI when compiling
+for the `wasm32-unknown-unknown` target.
+
+This makes it possible to be ABI-compatible with all other spec-compliant Wasm
+like Rusts `wasm32-wasi`.
+
+This compiler flag is perma-unstable, as it will be enabled by default in the
+future with no option to fall back to the old non-spec-compliant ABI.