From eea6149e03401c4a94a213112fb0694e3f44991b Mon Sep 17 00:00:00 2001
From: Soveu <marx.tomasz@gmail.com>
Date: Thu, 14 Sep 2023 23:21:39 +0200
Subject: [PATCH] Enable varargs support for AAPCS calling convention

This is the default calling convention for ARM - it is used for extern "C",
therefore it supports varargs.
---
 compiler/rustc_hir_analysis/src/lib.rs    | 2 +-
 compiler/rustc_target/src/spec/abi.rs     | 3 ++-
 tests/ui/c-variadic/variadic-ffi-2.rs     | 5 ++++-
 tests/ui/c-variadic/variadic-ffi-2.stderr | 2 +-
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/compiler/rustc_hir_analysis/src/lib.rs b/compiler/rustc_hir_analysis/src/lib.rs
index b0f333b79ca..ef788935efb 100644
--- a/compiler/rustc_hir_analysis/src/lib.rs
+++ b/compiler/rustc_hir_analysis/src/lib.rs
@@ -117,7 +117,7 @@
 fluent_messages! { "../messages.ftl" }
 
 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
-    const CONVENTIONS_UNSTABLE: &str = "`C`, `cdecl`, `win64`, `sysv64` or `efiapi`";
+    const CONVENTIONS_UNSTABLE: &str = "`C`, `cdecl`, `aapcs`, `win64`, `sysv64` or `efiapi`";
     const CONVENTIONS_STABLE: &str = "`C` or `cdecl`";
     const UNSTABLE_EXPLAIN: &str =
         "using calling conventions other than `C` or `cdecl` for varargs functions is unstable";
diff --git a/compiler/rustc_target/src/spec/abi.rs b/compiler/rustc_target/src/spec/abi.rs
index 956a5cb5c2f..a99cccd42c4 100644
--- a/compiler/rustc_target/src/spec/abi.rs
+++ b/compiler/rustc_target/src/spec/abi.rs
@@ -68,7 +68,7 @@ pub enum Abi {
 impl Abi {
     pub fn supports_varargs(self) -> bool {
         // * C and Cdecl obviously support varargs.
-        // * C can be based on SysV64 or Win64, so they must support varargs.
+        // * C can be based on Aapcs, SysV64 or Win64, so they must support varargs.
         // * EfiApi is based on Win64 or C, so it also supports it.
         //
         // * Stdcall does not, because it would be impossible for the callee to clean
@@ -79,6 +79,7 @@ pub fn supports_varargs(self) -> bool {
         match self {
             Self::C { .. }
             | Self::Cdecl { .. }
+            | Self::Aapcs { .. }
             | Self::Win64 { .. }
             | Self::SysV64 { .. }
             | Self::EfiApi => true,
diff --git a/tests/ui/c-variadic/variadic-ffi-2.rs b/tests/ui/c-variadic/variadic-ffi-2.rs
index c34b7e55f6a..67a0a9a1dec 100644
--- a/tests/ui/c-variadic/variadic-ffi-2.rs
+++ b/tests/ui/c-variadic/variadic-ffi-2.rs
@@ -3,10 +3,13 @@
 
 fn baz(f: extern "stdcall" fn(usize, ...)) {
     //~^ ERROR: C-variadic function must have a compatible calling convention,
-    // like C, cdecl, win64, sysv64 or efiapi
+    // like C, cdecl, aapcs, win64, sysv64 or efiapi
     f(22, 44);
 }
 
+fn aapcs(f: extern "aapcs" fn(usize, ...)) {
+    f(22, 44);
+}
 fn sysv(f: extern "sysv64" fn(usize, ...)) {
     f(22, 44);
 }
diff --git a/tests/ui/c-variadic/variadic-ffi-2.stderr b/tests/ui/c-variadic/variadic-ffi-2.stderr
index e21001ecaf8..8884fc6fb2a 100644
--- a/tests/ui/c-variadic/variadic-ffi-2.stderr
+++ b/tests/ui/c-variadic/variadic-ffi-2.stderr
@@ -1,4 +1,4 @@
-error[E0045]: C-variadic function must have a compatible calling convention, like `C`, `cdecl`, `win64`, `sysv64` or `efiapi`
+error[E0045]: C-variadic function must have a compatible calling convention, like `C`, `cdecl`, `aapcs`, `win64`, `sysv64` or `efiapi`
   --> $DIR/variadic-ffi-2.rs:4:11
    |
 LL | fn baz(f: extern "stdcall" fn(usize, ...)) {