Rollup merge of #142146 - workingjubilee:doubt-that-cmse-nonsecure-abis-always-match-c, r=compiler-errors

Withdraw the claim `extern "C-cmse-nonsecure-*"` always matches `extern "C"`

We currently claim that `extern "C-cmse-nonsecure-*"` ABIs will always match `extern "C"`, but that seems... **optimistic** when one considers that `extern "C"` is ambiguous enough to be redefined in ways we may not want the Cortex M Security Extensions ABIs to mirror. If some configuration, feature, or other platform quirk that applied to Arm CPUs with CMSE would modify the `extern "C"` ABI, it does not seem like we should guarantee that also applies to the `extern "cmse-nonsecure-*"` ABIs. Anything involving target modifiers that might affect register availability or usage could make us liars if, for instance, clang decides those apply to normal C functions but not ones with the CMSE attributes, but we still want to have interop with the C compiler.

We simply do not control enough of the factors involved to both force these ABIs to match and still provide useful interop, so we shouldn't implicitly promise they do. We should leave this judgement call to the decisions of platform experts who can afford to keep up with the latest news from Cambridge, instead of enshrining today's hopeful guess forever in Rust's permitted ABIs.

It's a bit weird anyways.
- The attributes are `__attribute__((cmse_nonsecure_call))` and `__attribute__((cmse_nonsecure_entry))`, so the obvious choice is `extern "cmse-nonsecure-call"` and `extern "cmse-nonsecure-entry"`.
- We do not prefix any other ABI that reflects (or even *is*) a C ABI with "C-", with the exception of the Rust-defined `extern "C-unwind`", e.g. we do not have `extern "C-aapcs"` or `extern "C-sysv64"`.

Tracking issues:
- rust-lang/rust#75835
- rust-lang/rust#81391

16 files changed, 46 insertions, 44 deletions

diff --git a/compiler/rustc_abi/src/canon_abi.rs b/compiler/rustc_abi/src/canon_abi.rs
index 7c020be6761..13f9a04b286 100644
--- a/compiler/rustc_abi/src/canon_abi.rs
+++ b/compiler/rustc_abi/src/canon_abi.rs
@@ -63,8 +63,8 @@ impl fmt::Display for CanonAbi {
             CanonAbi::Custom => ExternAbi::Custom,
             CanonAbi::Arm(arm_call) => match arm_call {
                 ArmCall::Aapcs => ExternAbi::Aapcs { unwind: false },
-                ArmCall::CCmseNonSecureCall => ExternAbi::CCmseNonSecureCall,
-                ArmCall::CCmseNonSecureEntry => ExternAbi::CCmseNonSecureEntry,
+                ArmCall::CCmseNonSecureCall => ExternAbi::CmseNonSecureCall,
+                ArmCall::CCmseNonSecureEntry => ExternAbi::CmseNonSecureEntry,
             },
             CanonAbi::GpuKernel => ExternAbi::GpuKernel,
             CanonAbi::Interrupt(interrupt_kind) => match interrupt_kind {
diff --git a/compiler/rustc_abi/src/extern_abi.rs b/compiler/rustc_abi/src/extern_abi.rs
index 1b8c2de1588..29a3678abf3 100644
--- a/compiler/rustc_abi/src/extern_abi.rs
+++ b/compiler/rustc_abi/src/extern_abi.rs
@@ -59,9 +59,9 @@ pub enum ExternAbi {
         unwind: bool,
     },
     /// extremely constrained barely-C ABI for TrustZone
-    CCmseNonSecureCall,
+    CmseNonSecureCall,
     /// extremely constrained barely-C ABI for TrustZone
-    CCmseNonSecureEntry,
+    CmseNonSecureEntry,
 
     /* gpu */
     /// An entry-point function called by the GPU's host
@@ -140,8 +140,6 @@ macro_rules! abi_impls {
 abi_impls! {
     ExternAbi = {
             C { unwind: false } =><= "C",
-            CCmseNonSecureCall =><= "C-cmse-nonsecure-call",
-            CCmseNonSecureEntry =><= "C-cmse-nonsecure-entry",
             C { unwind: true } =><= "C-unwind",
             Rust =><= "Rust",
             Aapcs { unwind: false } =><= "aapcs",
@@ -150,6 +148,8 @@ abi_impls! {
             AvrNonBlockingInterrupt =><= "avr-non-blocking-interrupt",
             Cdecl { unwind: false } =><= "cdecl",
             Cdecl { unwind: true } =><= "cdecl-unwind",
+            CmseNonSecureCall =><= "cmse-nonsecure-call",
+            CmseNonSecureEntry =><= "cmse-nonsecure-entry",
             Custom =><= "custom",
             EfiApi =><= "efiapi",
             Fastcall { unwind: false } =><= "fastcall",
diff --git a/compiler/rustc_ast_lowering/src/stability.rs b/compiler/rustc_ast_lowering/src/stability.rs
index 9b60807e650..6752218fa0d 100644
--- a/compiler/rustc_ast_lowering/src/stability.rs
+++ b/compiler/rustc_ast_lowering/src/stability.rs
@@ -127,12 +127,12 @@ pub fn extern_abi_stability(abi: ExternAbi) -> Result<(), UnstableAbi> {
             feature: sym::abi_riscv_interrupt,
             explain: GateReason::Experimental,
         }),
-        ExternAbi::CCmseNonSecureCall => Err(UnstableAbi {
+        ExternAbi::CmseNonSecureCall => Err(UnstableAbi {
             abi,
-            feature: sym::abi_c_cmse_nonsecure_call,
+            feature: sym::abi_cmse_nonsecure_call,
             explain: GateReason::Experimental,
         }),
-        ExternAbi::CCmseNonSecureEntry => Err(UnstableAbi {
+        ExternAbi::CmseNonSecureEntry => Err(UnstableAbi {
             abi,
             feature: sym::cmse_nonsecure_entry,
             explain: GateReason::Experimental,
diff --git a/compiler/rustc_error_codes/src/error_codes/E0775.md b/compiler/rustc_error_codes/src/error_codes/E0775.md
index efbd51e89ea..9fcd3a6eef7 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0775.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0775.md
@@ -8,7 +8,7 @@ Erroneous code example:
 ```ignore (no longer emitted)
 #![feature(cmse_nonsecure_entry)]
 
-pub extern "C-cmse-nonsecure-entry" fn entry_function() {}
+pub extern "cmse-nonsecure-entry" fn entry_function() {}
 ```
 
 To fix this error, compile your code for a Rust target that supports the
diff --git a/compiler/rustc_error_codes/src/error_codes/E0781.md b/compiler/rustc_error_codes/src/error_codes/E0781.md
index 7641acfb524..22abe0e3cb1 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0781.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0781.md
@@ -1,12 +1,12 @@
-The `C-cmse-nonsecure-call` ABI can only be used with function pointers.
+The `cmse-nonsecure-call` ABI can only be used with function pointers.
 
 Erroneous code example:
 
 ```compile_fail,E0781
-#![feature(abi_c_cmse_nonsecure_call)]
+#![feature(abi_cmse_nonsecure_call)]
 
-pub extern "C-cmse-nonsecure-call" fn test() {}
+pub extern "cmse-nonsecure-call" fn test() {}
 ```
 
-The `C-cmse-nonsecure-call` ABI should be used by casting function pointers to
+The `cmse-nonsecure-call` ABI should be used by casting function pointers to
 specific addresses.
diff --git a/compiler/rustc_error_codes/src/error_codes/E0798.md b/compiler/rustc_error_codes/src/error_codes/E0798.md
index da08cde3010..e5f356ef4d5 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0798.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0798.md
@@ -1,4 +1,4 @@
-Functions marked as `C-cmse-nonsecure-call` place restrictions on their
+Functions marked as `cmse-nonsecure-call` place restrictions on their
 inputs and outputs.
 
 - inputs must fit in the 4 available 32-bit argument registers. Alignment
@@ -12,12 +12,12 @@ see [arm's aapcs32](https://github.com/ARM-software/abi-aa/releases).
 
 Erroneous code example:
 
-```ignore (only fails on supported targets)
-#![feature(abi_c_cmse_nonsecure_call)]
+```ignore (host errors will not match for target)
+#![feature(abi_cmse_nonsecure_call)]
 
 #[no_mangle]
 pub fn test(
-    f: extern "C-cmse-nonsecure-call" fn(u32, u32, u32, u32, u32) -> u32,
+    f: extern "cmse-nonsecure-call" fn(u32, u32, u32, u32, u32) -> u32,
 ) -> u32 {
     f(1, 2, 3, 4, 5)
 }
@@ -27,12 +27,12 @@ Arguments' alignment is respected. In the example below, padding is inserted
 so that the `u64` argument is passed in registers r2 and r3. There is then no
 room left for the final `f32` argument
 
-```ignore (only fails on supported targets)
-#![feature(abi_c_cmse_nonsecure_call)]
+```ignore (host errors will not match for target)
+#![feature(abi_cmse_nonsecure_call)]
 
 #[no_mangle]
 pub fn test(
-    f: extern "C-cmse-nonsecure-call" fn(u32, u64, f32) -> u32,
+    f: extern "cmse-nonsecure-call" fn(u32, u64, f32) -> u32,
 ) -> u32 {
     f(1, 2, 3.0)
 }
diff --git a/compiler/rustc_error_codes/src/lib.rs b/compiler/rustc_error_codes/src/lib.rs
index 22cc1e894da..0aff1c06e0a 100644
--- a/compiler/rustc_error_codes/src/lib.rs
+++ b/compiler/rustc_error_codes/src/lib.rs
@@ -690,5 +690,5 @@ E0805: 0805,
 //  E0723, // unstable feature in `const` context
 //  E0738, // Removed; errored on `#[track_caller] fn`s in `extern "Rust" { ... }`.
 //  E0744, // merged into E0728
-//  E0776, // Removed; cmse_nonsecure_entry is now `C-cmse-nonsecure-entry`
+//  E0776, // Removed; `#[cmse_nonsecure_entry]` is now `extern "cmse-nonsecure-entry"`
 //  E0796, // unused error code. We use `static_mut_refs` lint instead.
diff --git a/compiler/rustc_feature/src/removed.rs b/compiler/rustc_feature/src/removed.rs
index c54b831e244..ddb99585bc2 100644
--- a/compiler/rustc_feature/src/removed.rs
+++ b/compiler/rustc_feature/src/removed.rs
@@ -54,6 +54,7 @@ declare_features! (
 
     /// Allows using the `amdgpu-kernel` ABI.
     (removed, abi_amdgpu_kernel, "1.77.0", Some(51575), None, 120495),
+    (removed, abi_c_cmse_nonsecure_call, "CURRENT_RUSTC_VERSION", Some(81391), Some("renamed to abi_cmse_nonsecure_call"), 142146),
     (removed, advanced_slice_patterns, "1.42.0", Some(62254),
      Some("merged into `#![feature(slice_patterns)]`"), 67712),
     (removed, allocator, "1.0.0", None, None),
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index d9d5334615a..e73a4e1766c 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -353,8 +353,8 @@ declare_features! (
 
     /// Allows `extern "avr-interrupt" fn()` and `extern "avr-non-blocking-interrupt" fn()`.
     (unstable, abi_avr_interrupt, "1.45.0", Some(69664)),
-    /// Allows `extern "C-cmse-nonsecure-call" fn()`.
-    (unstable, abi_c_cmse_nonsecure_call, "1.51.0", Some(81391)),
+    /// Allows `extern "cmse-nonsecure-call" fn()`.
+    (unstable, abi_cmse_nonsecure_call, "CURRENT_RUSTC_VERSION", Some(81391)),
     /// Allows `extern "custom" fn()`.
     (unstable, abi_custom, "CURRENT_RUSTC_VERSION", Some(140829)),
     /// Allows `extern "gpu-kernel" fn()`.
@@ -431,7 +431,7 @@ declare_features! (
     (unstable, closure_lifetime_binder, "1.64.0", Some(97362)),
     /// Allows `#[track_caller]` on closures and coroutines.
     (unstable, closure_track_caller, "1.57.0", Some(87417)),
-    /// Allows `extern "C-cmse-nonsecure-entry" fn()`.
+    /// Allows `extern "cmse-nonsecure-entry" fn()`.
     (unstable, cmse_nonsecure_entry, "1.48.0", Some(75835)),
     /// Allows `async {}` expressions in const contexts.
     (unstable, const_async_blocks, "1.53.0", Some(85368)),
diff --git a/compiler/rustc_hir_analysis/messages.ftl b/compiler/rustc_hir_analysis/messages.ftl
index 8c43d10b9e4..4ec2bbfc5ab 100644
--- a/compiler/rustc_hir_analysis/messages.ftl
+++ b/compiler/rustc_hir_analysis/messages.ftl
@@ -73,10 +73,10 @@ hir_analysis_closure_implicit_hrtb = implicit types in closure signatures are fo
     .label = `for<...>` is here
 
 hir_analysis_cmse_call_generic =
-    function pointers with the `"C-cmse-nonsecure-call"` ABI cannot contain generics in their type
+    function pointers with the `"cmse-nonsecure-call"` ABI cannot contain generics in their type
 
 hir_analysis_cmse_entry_generic =
-    functions with the `"C-cmse-nonsecure-entry"` ABI cannot contain generics in their type
+    functions with the `"cmse-nonsecure-entry"` ABI cannot contain generics in their type
 
 hir_analysis_cmse_inputs_stack_spill =
     arguments for `{$abi}` function too large to pass via registers
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/cmse.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/cmse.rs
index ebeb3b58208..82e5f65476f 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/cmse.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/cmse.rs
@@ -18,7 +18,7 @@ pub(crate) fn validate_cmse_abi<'tcx>(
     fn_sig: ty::PolyFnSig<'tcx>,
 ) {
     match abi {
-        ExternAbi::CCmseNonSecureCall => {
+        ExternAbi::CmseNonSecureCall => {
             let hir_node = tcx.hir_node(hir_id);
             let hir::Node::Ty(hir::Ty {
                 span: bare_fn_span,
@@ -38,7 +38,7 @@ pub(crate) fn validate_cmse_abi<'tcx>(
                     dcx,
                     span,
                     E0781,
-                    "the `\"C-cmse-nonsecure-call\"` ABI is only allowed on function pointers"
+                    "the `\"cmse-nonsecure-call\"` ABI is only allowed on function pointers"
                 )
                 .emit();
                 return;
@@ -78,7 +78,7 @@ pub(crate) fn validate_cmse_abi<'tcx>(
                 }
             };
         }
-        ExternAbi::CCmseNonSecureEntry => {
+        ExternAbi::CmseNonSecureEntry => {
             let hir_node = tcx.hir_node(hir_id);
             let Some(hir::FnSig { decl, span: fn_sig_span, .. }) = hir_node.fn_sig() else {
                 // might happen when this ABI is used incorrectly. That will be handled elsewhere
@@ -203,11 +203,11 @@ fn should_emit_generic_error<'tcx>(abi: ExternAbi, layout_err: &'tcx LayoutError
     match layout_err {
         TooGeneric(ty) => {
             match abi {
-                ExternAbi::CCmseNonSecureCall => {
+                ExternAbi::CmseNonSecureCall => {
                     // prevent double reporting of this error
                     !ty.is_impl_trait()
                 }
-                ExternAbi::CCmseNonSecureEntry => true,
+                ExternAbi::CmseNonSecureEntry => true,
                 _ => bug!("invalid ABI: {abi}"),
             }
         }
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index 5cb943b0d8c..90b832df281 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -1248,13 +1248,13 @@ pub fn fn_can_unwind(tcx: TyCtxt<'_>, fn_def_id: Option<DefId>, abi: ExternAbi)
         | EfiApi
         | AvrInterrupt
         | AvrNonBlockingInterrupt
+        | CmseNonSecureCall
+        | CmseNonSecureEntry
+        | Custom
         | RiscvInterruptM
         | RiscvInterruptS
-        | CCmseNonSecureCall
-        | CCmseNonSecureEntry
-        | Custom
-        | Unadjusted
-        | RustInvalid => false,
+        | RustInvalid
+        | Unadjusted => false,
         Rust | RustCall | RustCold => tcx.sess.panic_strategy() == PanicStrategy::Unwind,
     }
 }
diff --git a/compiler/rustc_smir/src/rustc_internal/internal.rs b/compiler/rustc_smir/src/rustc_internal/internal.rs
index c0d9937e34d..24351eee1c4 100644
--- a/compiler/rustc_smir/src/rustc_internal/internal.rs
+++ b/compiler/rustc_smir/src/rustc_internal/internal.rs
@@ -479,6 +479,8 @@ impl RustcInternal for Abi {
             Abi::Vectorcall { unwind } => rustc_abi::ExternAbi::Vectorcall { unwind },
             Abi::Thiscall { unwind } => rustc_abi::ExternAbi::Thiscall { unwind },
             Abi::Aapcs { unwind } => rustc_abi::ExternAbi::Aapcs { unwind },
+            Abi::CCmseNonSecureCall => rustc_abi::ExternAbi::CmseNonSecureCall,
+            Abi::CCmseNonSecureEntry => rustc_abi::ExternAbi::CmseNonSecureEntry,
             Abi::Win64 { unwind } => rustc_abi::ExternAbi::Win64 { unwind },
             Abi::SysV64 { unwind } => rustc_abi::ExternAbi::SysV64 { unwind },
             Abi::PtxKernel => rustc_abi::ExternAbi::PtxKernel,
@@ -488,8 +490,6 @@ impl RustcInternal for Abi {
             Abi::EfiApi => rustc_abi::ExternAbi::EfiApi,
             Abi::AvrInterrupt => rustc_abi::ExternAbi::AvrInterrupt,
             Abi::AvrNonBlockingInterrupt => rustc_abi::ExternAbi::AvrNonBlockingInterrupt,
-            Abi::CCmseNonSecureCall => rustc_abi::ExternAbi::CCmseNonSecureCall,
-            Abi::CCmseNonSecureEntry => rustc_abi::ExternAbi::CCmseNonSecureEntry,
             Abi::System { unwind } => rustc_abi::ExternAbi::System { unwind },
             Abi::RustCall => rustc_abi::ExternAbi::RustCall,
             Abi::Unadjusted => rustc_abi::ExternAbi::Unadjusted,
diff --git a/compiler/rustc_smir/src/rustc_smir/convert/ty.rs b/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
index 2c652c7546e..7abec488151 100644
--- a/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
+++ b/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
@@ -871,8 +871,8 @@ impl<'tcx> Stable<'tcx> for rustc_abi::ExternAbi {
             ExternAbi::EfiApi => Abi::EfiApi,
             ExternAbi::AvrInterrupt => Abi::AvrInterrupt,
             ExternAbi::AvrNonBlockingInterrupt => Abi::AvrNonBlockingInterrupt,
-            ExternAbi::CCmseNonSecureCall => Abi::CCmseNonSecureCall,
-            ExternAbi::CCmseNonSecureEntry => Abi::CCmseNonSecureEntry,
+            ExternAbi::CmseNonSecureCall => Abi::CCmseNonSecureCall,
+            ExternAbi::CmseNonSecureEntry => Abi::CCmseNonSecureEntry,
             ExternAbi::System { unwind } => Abi::System { unwind },
             ExternAbi::RustCall => Abi::RustCall,
             ExternAbi::Unadjusted => Abi::Unadjusted,
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index c9262d24a17..11463ad354a 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -406,6 +406,7 @@ symbols! {
         abi_amdgpu_kernel,
         abi_avr_interrupt,
         abi_c_cmse_nonsecure_call,
+        abi_cmse_nonsecure_call,
         abi_custom,
         abi_efiapi,
         abi_gpu_kernel,
diff --git a/compiler/rustc_target/src/spec/abi_map.rs b/compiler/rustc_target/src/spec/abi_map.rs
index ce1bdcbb8ac..fde3adb034d 100644
--- a/compiler/rustc_target/src/spec/abi_map.rs
+++ b/compiler/rustc_target/src/spec/abi_map.rs
@@ -93,13 +93,13 @@ impl AbiMap {
             (ExternAbi::Aapcs { .. }, Arch::Arm(..)) => CanonAbi::Arm(ArmCall::Aapcs),
             (ExternAbi::Aapcs { .. }, _) => return AbiMapping::Invalid,
 
-            (ExternAbi::CCmseNonSecureCall, Arch::Arm(ArmVer::ThumbV8M)) => {
+            (ExternAbi::CmseNonSecureCall, Arch::Arm(ArmVer::ThumbV8M)) => {
                 CanonAbi::Arm(ArmCall::CCmseNonSecureCall)
             }
-            (ExternAbi::CCmseNonSecureEntry, Arch::Arm(ArmVer::ThumbV8M)) => {
+            (ExternAbi::CmseNonSecureEntry, Arch::Arm(ArmVer::ThumbV8M)) => {
                 CanonAbi::Arm(ArmCall::CCmseNonSecureEntry)
             }
-            (ExternAbi::CCmseNonSecureCall | ExternAbi::CCmseNonSecureEntry, ..) => {
+            (ExternAbi::CmseNonSecureCall | ExternAbi::CmseNonSecureEntry, ..) => {
                 return AbiMapping::Invalid;
             }