Auto merge of #105381 - uweigand:s390x-ffi-vaarg, r=nikic

Implement va_list and va_arg for s390x FFI

Following the s390x ELF ABI and based on the clang implementation, provide appropriate definitions of va_list in library/core/src/ffi/mod.rs and va_arg handling in compiler/rustc_codegen_llvm/src/va_arg.rs.

Fixes the following test cases on s390x:
src/test/run-make-fulldeps/c-link-to-rust-va-list-fn src/test/ui/abi/variadic-ffi.rs

Fixes rust-lang/rust#84628.

Author: bors

core/src/ffi/mod.rs

@@ -227,7 +227,12 @@ impl fmt::Debug for c_void {
 /// Basic implementation of a `va_list`.
 // The name is WIP, using `VaListImpl` for now.
 #[cfg(any(
-    all(not(target_arch = "aarch64"), not(target_arch = "powerpc"), not(target_arch = "x86_64")),
+    all(
+        not(target_arch = "aarch64"),
+        not(target_arch = "powerpc"),
+        not(target_arch = "s390x"),
+        not(target_arch = "x86_64")
+    ),
     all(target_arch = "aarch64", any(target_os = "macos", target_os = "ios")),
     target_family = "wasm",
     target_arch = "asmjs",
@@ -251,7 +256,12 @@ pub struct VaListImpl<'f> {
 }
 
 #[cfg(any(
-    all(not(target_arch = "aarch64"), not(target_arch = "powerpc"), not(target_arch = "x86_64")),
+    all(
+        not(target_arch = "aarch64"),
+        not(target_arch = "powerpc"),
+        not(target_arch = "s390x"),
+        not(target_arch = "x86_64")
+    ),
     all(target_arch = "aarch64", any(target_os = "macos", target_os = "ios")),
     target_family = "wasm",
     target_arch = "asmjs",
@@ -319,6 +329,25 @@ pub struct VaListImpl<'f> {
     _marker: PhantomData<&'f mut &'f c_void>,
 }
 
+/// s390x ABI implementation of a `va_list`.
+#[cfg(target_arch = "s390x")]
+#[repr(C)]
+#[derive(Debug)]
+#[unstable(
+    feature = "c_variadic",
+    reason = "the `c_variadic` feature has not been properly tested on \
+              all supported platforms",
+    issue = "44930"
+)]
+#[lang = "va_list"]
+pub struct VaListImpl<'f> {
+    gpr: i64,
+    fpr: i64,
+    overflow_arg_area: *mut c_void,
+    reg_save_area: *mut c_void,
+    _marker: PhantomData<&'f mut &'f c_void>,
+}
+
 /// x86_64 ABI implementation of a `va_list`.
 #[cfg(all(target_arch = "x86_64", not(target_os = "uefi"), not(windows)))]
 #[repr(C)]
@@ -352,6 +381,7 @@ pub struct VaList<'a, 'f: 'a> {
         all(
             not(target_arch = "aarch64"),
             not(target_arch = "powerpc"),
+            not(target_arch = "s390x"),
             not(target_arch = "x86_64")
         ),
         all(target_arch = "aarch64", any(target_os = "macos", target_os = "ios")),
@@ -363,7 +393,12 @@ pub struct VaList<'a, 'f: 'a> {
     inner: VaListImpl<'f>,
 
     #[cfg(all(
-        any(target_arch = "aarch64", target_arch = "powerpc", target_arch = "x86_64"),
+        any(
+            target_arch = "aarch64",
+            target_arch = "powerpc",
+            target_arch = "s390x",
+            target_arch = "x86_64"
+        ),
         any(not(target_arch = "aarch64"), not(any(target_os = "macos", target_os = "ios"))),
         not(target_family = "wasm"),
         not(target_arch = "asmjs"),
@@ -376,7 +411,12 @@ pub struct VaList<'a, 'f: 'a> {
 }
 
 #[cfg(any(
-    all(not(target_arch = "aarch64"), not(target_arch = "powerpc"), not(target_arch = "x86_64")),
+    all(
+        not(target_arch = "aarch64"),
+        not(target_arch = "powerpc"),
+        not(target_arch = "s390x"),
+        not(target_arch = "x86_64")
+    ),
     all(target_arch = "aarch64", any(target_os = "macos", target_os = "ios")),
     target_family = "wasm",
     target_arch = "asmjs",
@@ -398,7 +438,12 @@ impl<'f> VaListImpl<'f> {
 }
 
 #[cfg(all(
-    any(target_arch = "aarch64", target_arch = "powerpc", target_arch = "x86_64"),
+    any(
+        target_arch = "aarch64",
+        target_arch = "powerpc",
+        target_arch = "s390x",
+        target_arch = "x86_64"
+    ),
     any(not(target_arch = "aarch64"), not(any(target_os = "macos", target_os = "ios"))),
     not(target_family = "wasm"),
     not(target_arch = "asmjs"),