Aarch64 call abi does not zeroext (and one cannot assume it does so)

compiler/rustc_target/src/abi/call/aarch64.rs

@@ -1,6 +1,27 @@
 use crate::abi::call::{ArgAbi, FnAbi, Reg, RegKind, Uniform};
 use crate::abi::{HasDataLayout, TyAbiInterface};
 
+/// Given integer-types M and register width N (e.g. M=u16 and N=32 bits), the
+/// `ParamExtension` policy specifies how a uM value should be treated when
+/// passed via register or stack-slot of width N. See also rust-lang/rust#97463.
+#[derive(Copy, Clone, PartialEq)]
+pub enum ParamExtension {
+    /// Indicates that when passing an i8/i16, either as a function argument or
+    /// as a return value, it must be sign-extended to 32 bits, and likewise a
+    /// u8/u16 must be zero-extended to 32-bits. (This variant is here to
+    /// accommodate Apple's deviation from the usual AArch64 ABI as defined by
+    /// ARM.)
+    ///
+    /// See also: <https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms#Pass-Arguments-to-Functions-Correctly>
+    ExtendTo32Bits,
+
+    /// Indicates that no sign- nor zero-extension is performed: if a value of
+    /// type with bitwidth M is passed as function argument or return value,
+    /// then M bits are copied into the least significant M bits, and the
+    /// remaining bits of the register (or word of memory) are untouched.
+    NoExtension,
+}
+
 fn is_homogeneous_aggregate<'a, Ty, C>(cx: &C, arg: &mut ArgAbi<'a, Ty>) -> Option<Uniform>
 where
     Ty: TyAbiInterface<'a, C> + Copy,
@@ -24,13 +45,16 @@ where
     })
 }
 
-fn classify_ret<'a, Ty, C>(cx: &C, ret: &mut ArgAbi<'a, Ty>)
+fn classify_ret<'a, Ty, C>(cx: &C, ret: &mut ArgAbi<'a, Ty>, param_policy: ParamExtension)
 where
     Ty: TyAbiInterface<'a, C> + Copy,
     C: HasDataLayout,
 {
     if !ret.layout.is_aggregate() {
-        ret.extend_integer_width_to(32);
+        match param_policy {
+            ParamExtension::ExtendTo32Bits => ret.extend_integer_width_to(32),
+            ParamExtension::NoExtension => {}
+        }
         return;
     }
     if let Some(uniform) = is_homogeneous_aggregate(cx, ret) {
@@ -46,13 +70,16 @@ where
     ret.make_indirect();
 }
 
-fn classify_arg<'a, Ty, C>(cx: &C, arg: &mut ArgAbi<'a, Ty>)
+fn classify_arg<'a, Ty, C>(cx: &C, arg: &mut ArgAbi<'a, Ty>, param_policy: ParamExtension)
 where
     Ty: TyAbiInterface<'a, C> + Copy,
     C: HasDataLayout,
 {
     if !arg.layout.is_aggregate() {
-        arg.extend_integer_width_to(32);
+        match param_policy {
+            ParamExtension::ExtendTo32Bits => arg.extend_integer_width_to(32),
+            ParamExtension::NoExtension => {}
+        }
         return;
     }
     if let Some(uniform) = is_homogeneous_aggregate(cx, arg) {
@@ -68,19 +95,19 @@ where
     arg.make_indirect();
 }
 
-pub fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
+pub fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>, param_policy: ParamExtension)
 where
     Ty: TyAbiInterface<'a, C> + Copy,
     C: HasDataLayout,
 {
     if !fn_abi.ret.is_ignore() {
-        classify_ret(cx, &mut fn_abi.ret);
+        classify_ret(cx, &mut fn_abi.ret, param_policy);
     }
 
     for arg in &mut fn_abi.args {
         if arg.is_ignore() {
             continue;
         }
-        classify_arg(cx, arg);
+        classify_arg(cx, arg, param_policy);
     }
 }

compiler/rustc_target/src/abi/call/mod.rs

@@ -687,7 +687,14 @@ impl<'a, Ty> FnAbi<'a, Ty> {
                     }
                 }
             },
-            "aarch64" => aarch64::compute_abi_info(cx, self),
+            "aarch64" => {
+                let param_policy = if cx.target_spec().is_like_osx {
+                    aarch64::ParamExtension::ExtendTo32Bits
+                } else {
+                    aarch64::ParamExtension::NoExtension
+                };
+                aarch64::compute_abi_info(cx, self, param_policy)
+            }
             "amdgpu" => amdgpu::compute_abi_info(cx, self),
             "arm" => arm::compute_abi_info(cx, self),
             "avr" => avr::compute_abi_info(self),

compiler/rustc_target/src/spec/mod.rs

@@ -1250,6 +1250,8 @@ pub struct TargetOptions {
     pub abi_return_struct_as_int: bool,
     /// Whether the target toolchain is like macOS's. Only useful for compiling against iOS/macOS,
     /// in particular running dsymutil and some other stuff like `-dead_strip`. Defaults to false.
+    /// Also indiates whether to use Apple-specific ABI changes, such as extending function
+    /// parameters to 32-bits.
     pub is_like_osx: bool,
     /// Whether the target toolchain is like Solaris's.
     /// Only useful for compiling against Illumos/Solaris,

src/test/auxiliary/rust_test_helpers.c

@@ -1,6 +1,7 @@
 // Helper functions used only in tests
 
 #include <stdint.h>
+#include <stdlib.h>
 #include <assert.h>
 #include <stdarg.h>
 
@@ -415,3 +416,14 @@ rust_dbg_unpack_option_u64u64(struct U8TaggedEnumOptionU64U64 o, uint64_t *a, ui
         return 0;
     }
 }
+
+uint16_t issue_97463_leak_uninit_data(uint32_t a, uint32_t b, uint32_t c) {
+    struct bloc { uint16_t a; uint16_t b; uint16_t c; };
+    struct bloc *data = malloc(sizeof(struct bloc));
+
+    data->a = a & 0xFFFF;
+    data->b = b & 0xFFFF;
+    data->c = c & 0xFFFF;
+
+    return data->b; /* leak data */
+}

src/test/codegen/abi-repr-ext.rs

@@ -1,14 +1,56 @@
 // compile-flags: -O
 
-#![crate_type="lib"]
+// revisions:x86_64 i686 aarch64-apple aarch64-windows aarch64-linux arm riscv
+
+//[x86_64] compile-flags: --target x86_64-unknown-uefi
+//[x86_64] needs-llvm-components: x86
+//[i686] compile-flags: --target i686-unknown-linux-musl
+//[i686] needs-llvm-components: x86
+//[aarch64-windows] compile-flags: --target aarch64-pc-windows-msvc
+//[aarch64-windows] needs-llvm-components: aarch64
+//[aarch64-linux] compile-flags: --target aarch64-unknown-linux-gnu
+//[aarch64-linux] needs-llvm-components: aarch64
+//[aarch64-apple] compile-flags: --target aarch64-apple-darwin
+//[aarch64-apple] needs-llvm-components: aarch64
+//[arm] compile-flags: --target armv7r-none-eabi
+//[arm] needs-llvm-components: arm
+//[riscv] compile-flags: --target riscv64gc-unknown-none-elf
+//[riscv] needs-llvm-components: riscv
+
+// See bottom of file for a corresponding C source file that is meant to yield
+// equivalent declarations.
+#![feature(no_core, lang_items)]
+#![crate_type = "lib"]
+#![no_std]
+#![no_core]
+
+#[lang="sized"] trait Sized { }
+#[lang="freeze"] trait Freeze { }
+#[lang="copy"] trait Copy { }
 
 #[repr(i8)]
 pub enum Type {
     Type1 = 0,
     Type2 = 1
 }
 
-// CHECK: define{{( dso_local)?}} noundef signext i8 @test()
+// To accommodate rust#97800, one might consider writing the below as:
+//
+// `define{{( dso_local)?}} noundef{{( signext)?}} i8 @test()`
+//
+// but based on rust#80556, it seems important to actually check for the
+// presence of the `signext` for those targets where we expect it.
+
+// CHECK: define{{( dso_local)?}} noundef
+// x86_64-SAME:                 signext
+// aarch64-apple-SAME:          signext
+// aarch64-windows-NOT: signext
+// aarch64-linux-NOT:   signext
+// arm-SAME:                    signext
+// riscv-SAME:                  signext
+// CHECK-SAME: i8 @test()
+
+
 #[no_mangle]
 pub extern "C" fn test() -> Type {
     Type::Type1

src/test/codegen/pic-relocation-model.rs

@@ -10,7 +10,10 @@ pub fn call_foreign_fn() -> u8 {
     }
 }
 
-// CHECK: declare zeroext i8 @foreign_fn()
+// (Allow but do not require `zeroext` here, because it is not worth effort to
+// spell out which targets have it and which ones do not; see rust#97800.)
+
+// CHECK: declare{{( zeroext)?}} i8 @foreign_fn()
 extern "C" {fn foreign_fn() -> u8;}
 
 // CHECK: !{i32 7, !"PIC Level", i32 2}