Rollup merge of rust-lang#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#75835
- rust-lang#81391

Author: jdonszelmann

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 {

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",

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,

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

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.

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)
 }

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.

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),

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)),

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