Auto merge of #81346 - hug-dev:nonsecure-call-abi, r=jonas-schievink

Add a new ABI to support cmse_nonsecure_call

This adds support for the `cmse_nonsecure_call` feature to be able to perform non-secure function call.

See the discussion on Zulip [here](https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Support.20for.20callsite.20attributes/near/223054928).

This is a followup to #75810 which added `cmse_nonsecure_entry`. As for that PR, I assume that the changes are small enough to not have to go through a RFC but I don't mind doing one if needed 😃
I did not yet create a tracking issue, but if most of it is fine, I can create one and update the various files accordingly (they refer to the other tracking issue now).

On the Zulip chat, I believe `@jonas-schievink` volunteered to be a reviewer 💯

Author: bors

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -156,6 +156,14 @@ impl<'a> PostExpansionVisitor<'a> {
                     "efiapi ABI is experimental and subject to change"
                 );
             }
+            "C-cmse-nonsecure-call" => {
+                gate_feature_post!(
+                    &self,
+                    abi_c_cmse_nonsecure_call,
+                    span,
+                    "C-cmse-nonsecure-call ABI is experimental and subject to change"
+                );
+            }
             abi => self
                 .sess
                 .parse_sess

compiler/rustc_codegen_cranelift/src/abi/mod.rs

@@ -28,6 +28,7 @@ fn clif_sig_from_fn_abi<'tcx>(
         Conv::X86_64SysV => CallConv::SystemV,
         Conv::X86_64Win64 => CallConv::WindowsFastcall,
         Conv::ArmAapcs
+        | Conv::CCmseNonSecureCall
         | Conv::Msp430Intr
         | Conv::PtxKernel
         | Conv::X86Fastcall

compiler/rustc_codegen_llvm/src/abi.rs

@@ -389,7 +389,7 @@ impl<'tcx> FnAbiLlvmExt<'tcx> for FnAbi<'tcx, Ty<'tcx>> {
 
     fn llvm_cconv(&self) -> llvm::CallConv {
         match self.conv {
-            Conv::C | Conv::Rust => llvm::CCallConv,
+            Conv::C | Conv::Rust | Conv::CCmseNonSecureCall => llvm::CCallConv,
             Conv::AmdGpuKernel => llvm::AmdGpuKernel,
             Conv::AvrInterrupt => llvm::AvrInterrupt,
             Conv::AvrNonBlockingInterrupt => llvm::AvrNonBlockingInterrupt,
@@ -546,6 +546,18 @@ impl<'tcx> FnAbiLlvmExt<'tcx> for FnAbi<'tcx, Ty<'tcx>> {
         if cconv != llvm::CCallConv {
             llvm::SetInstructionCallConv(callsite, cconv);
         }
+
+        if self.conv == Conv::CCmseNonSecureCall {
+            // This will probably get ignored on all targets but those supporting the TrustZone-M
+            // extension (thumbv8m targets).
+            unsafe {
+                llvm::AddCallSiteAttrString(
+                    callsite,
+                    llvm::AttributePlace::Function,
+                    rustc_data_structures::const_cstr!("cmse_nonsecure_call"),
+                );
+            }
+        }
     }
 }
 

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -1100,6 +1100,7 @@ extern "C" {
     // Operations on call sites
     pub fn LLVMSetInstructionCallConv(Instr: &Value, CC: c_uint);
     pub fn LLVMRustAddCallSiteAttribute(Instr: &Value, index: c_uint, attr: Attribute);
+    pub fn LLVMRustAddCallSiteAttrString(Instr: &Value, index: c_uint, Name: *const c_char);
     pub fn LLVMRustAddAlignmentCallSiteAttr(Instr: &Value, index: c_uint, bytes: u32);
     pub fn LLVMRustAddDereferenceableCallSiteAttr(Instr: &Value, index: c_uint, bytes: u64);
     pub fn LLVMRustAddDereferenceableOrNullCallSiteAttr(Instr: &Value, index: c_uint, bytes: u64);

compiler/rustc_codegen_llvm/src/llvm/mod.rs

@@ -43,6 +43,10 @@ pub fn AddFunctionAttrString(llfn: &'a Value, idx: AttributePlace, attr: &CStr)
     }
 }
 
+pub fn AddCallSiteAttrString(callsite: &Value, idx: AttributePlace, attr: &CStr) {
+    unsafe { LLVMRustAddCallSiteAttrString(callsite, idx.as_uint(), attr.as_ptr()) }
+}
+
 #[derive(Copy, Clone)]
 pub enum AttributePlace {
     ReturnValue,

compiler/rustc_error_codes/src/error_codes.rs

@@ -466,6 +466,7 @@ E0777: include_str!("./error_codes/E0777.md"),
 E0778: include_str!("./error_codes/E0778.md"),
 E0779: include_str!("./error_codes/E0779.md"),
 E0780: include_str!("./error_codes/E0780.md"),
+E0781: include_str!("./error_codes/E0781.md"),
 ;
 //  E0006, // merged with E0005
 //  E0008, // cannot bind by-move into a pattern guard

compiler/rustc_error_codes/src/error_codes/E0781.md

@@ -0,0 +1,12 @@
+The `C-cmse-nonsecure-call` ABI can only be used with function pointers.
+
+Erroneous code example:
+
+```compile_fail,E0781
+#![feature(abi_c_cmse_nonsecure_call)]
+
+pub extern "C-cmse-nonsecure-call" fn test() {}
+```
+
+The `C-cmse-nonsecure-call` ABI should be used by casting function pointers to
+specific addresses.

compiler/rustc_feature/src/active.rs

@@ -628,6 +628,9 @@ declare_features! (
 
     /// Allows using `pointer` and `reference` in intra-doc links
     (active, intra_doc_pointers, "1.51.0", Some(80896), None),
+
+    /// Allows `extern "C-cmse-nonsecure-call" fn()`.
+    (active, abi_c_cmse_nonsecure_call, "1.51.0", Some(81391), None),
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -216,6 +216,14 @@ extern "C" void LLVMRustAddCallSiteAttribute(LLVMValueRef Instr, unsigned Index,
   Call->addAttribute(Index, Attr);
 }
 
+extern "C" void LLVMRustAddCallSiteAttrString(LLVMValueRef Instr, unsigned Index,
+                                              const char *Name) {
+  CallBase *Call = unwrap<CallBase>(Instr);
+  Attribute Attr = Attribute::get(Call->getContext(), Name);
+  Call->addAttribute(Index, Attr);
+}
+
+
 extern "C" void LLVMRustAddAlignmentCallSiteAttr(LLVMValueRef Instr,
                                                  unsigned Index,
                                                  uint32_t Bytes) {

compiler/rustc_middle/src/ty/layout.rs

@@ -2650,6 +2650,7 @@ where
             Win64 => Conv::X86_64Win64,
             SysV64 => Conv::X86_64SysV,
             Aapcs => Conv::ArmAapcs,
+            CCmseNonSecureCall => Conv::CCmseNonSecureCall,
             PtxKernel => Conv::PtxKernel,
             Msp430Interrupt => Conv::Msp430Intr,
             X86Interrupt => Conv::X86Intr,