Auto merge of #49878 - dlrobertson:va_list_pt0, r=eddyb

libcore: Add VaList and variadic arg handling intrinsics

## Summary

 - Add intrinsics for `va_start`, `va_end`, `va_copy`, and `va_arg`.
 - Add `core::va_list::VaList` to `libcore`.

Part 1 of (at least) 3 for #44930

Comments and critiques are very much welcomed 😄

Author: bors

src/libcore/ffi.rs

@@ -1,6 +1,7 @@
 #![stable(feature = "", since = "1.30.0")]
 
 #![allow(non_camel_case_types)]
+#![cfg_attr(stage0, allow(dead_code))]
 
 //! Utilities related to FFI bindings.
 
@@ -40,3 +41,187 @@ impl fmt::Debug for c_void {
         f.pad("c_void")
     }
 }
+
+/// Basic implementation of a `va_list`.
+#[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
+              not(target_arch = "x86_64")),
+          windows))]
+#[unstable(feature = "c_variadic",
+           reason = "the `c_variadic` feature has not been properly tested on \
+                     all supported platforms",
+           issue = "27745")]
+extern {
+    type VaListImpl;
+}
+
+#[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
+              not(target_arch = "x86_64")),
+          windows))]
+impl fmt::Debug for VaListImpl {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "va_list* {:p}", self)
+    }
+}
+
+/// AArch64 ABI implementation of a `va_list`. See the
+/// [Aarch64 Procedure Call Standard] for more details.
+///
+/// [AArch64 Procedure Call Standard]:
+/// http://infocenter.arm.com/help/topic/com.arm.doc.ihi0055b/IHI0055B_aapcs64.pdf
+#[cfg(all(target_arch = "aarch64", not(windows)))]
+#[repr(C)]
+#[derive(Debug)]
+#[unstable(feature = "c_variadic",
+           reason = "the `c_variadic` feature has not been properly tested on \
+                     all supported platforms",
+           issue = "27745")]
+struct VaListImpl {
+    stack: *mut (),
+    gr_top: *mut (),
+    vr_top: *mut (),
+    gr_offs: i32,
+    vr_offs: i32,
+}
+
+/// PowerPC ABI implementation of a `va_list`.
+#[cfg(all(target_arch = "powerpc", not(windows)))]
+#[repr(C)]
+#[derive(Debug)]
+#[unstable(feature = "c_variadic",
+           reason = "the `c_variadic` feature has not been properly tested on \
+                     all supported platforms",
+           issue = "27745")]
+struct VaListImpl {
+    gpr: u8,
+    fpr: u8,
+    reserved: u16,
+    overflow_arg_area: *mut (),
+    reg_save_area: *mut (),
+}
+
+/// x86_64 ABI implementation of a `va_list`.
+#[cfg(all(target_arch = "x86_64", not(windows)))]
+#[repr(C)]
+#[derive(Debug)]
+#[unstable(feature = "c_variadic",
+           reason = "the `c_variadic` feature has not been properly tested on \
+                     all supported platforms",
+           issue = "27745")]
+struct VaListImpl {
+    gp_offset: i32,
+    fp_offset: i32,
+    overflow_arg_area: *mut (),
+    reg_save_area: *mut (),
+}
+
+/// A wrapper for a `va_list`
+#[lang = "va_list"]
+#[derive(Debug)]
+#[unstable(feature = "c_variadic",
+           reason = "the `c_variadic` feature has not been properly tested on \
+                     all supported platforms",
+           issue = "27745")]
+#[repr(transparent)]
+#[cfg(not(stage0))]
+pub struct VaList<'a>(&'a mut VaListImpl);
+
+// The VaArgSafe trait needs to be used in public interfaces, however, the trait
+// itself must not be allowed to be used outside this module. Allowing users to
+// implement the trait for a new type (thereby allowing the va_arg intrinsic to
+// be used on a new type) is likely to cause undefined behavior.
+//
+// FIXME(dlrobertson): In order to use the VaArgSafe trait in a public interface
+// but also ensure it cannot be used elsewhere, the trait needs to be public
+// within a private module. Once RFC 2145 has been implemented look into
+// improving this.
+mod sealed_trait {
+    /// Trait which whitelists the allowed types to be used with [VaList::arg]
+    ///
+    /// [VaList::va_arg]: struct.VaList.html#method.arg
+    #[unstable(feature = "c_variadic",
+               reason = "the `c_variadic` feature has not been properly tested on \
+                         all supported platforms",
+               issue = "27745")]
+    pub trait VaArgSafe {}
+}
+
+macro_rules! impl_va_arg_safe {
+    ($($t:ty),+) => {
+        $(
+            #[unstable(feature = "c_variadic",
+                       reason = "the `c_variadic` feature has not been properly tested on \
+                                 all supported platforms",
+                       issue = "27745")]
+            impl sealed_trait::VaArgSafe for $t {}
+        )+
+    }
+}
+
+impl_va_arg_safe!{i8, i16, i32, i64, usize}
+impl_va_arg_safe!{u8, u16, u32, u64, isize}
+impl_va_arg_safe!{f64}
+
+#[unstable(feature = "c_variadic",
+           reason = "the `c_variadic` feature has not been properly tested on \
+                     all supported platforms",
+           issue = "27745")]
+impl<T> sealed_trait::VaArgSafe for *mut T {}
+#[unstable(feature = "c_variadic",
+           reason = "the `c_variadic` feature has not been properly tested on \
+                     all supported platforms",
+           issue = "27745")]
+impl<T> sealed_trait::VaArgSafe for *const T {}
+
+#[cfg(not(stage0))]
+impl<'a> VaList<'a> {
+    /// Advance to the next arg.
+    #[unstable(feature = "c_variadic",
+               reason = "the `c_variadic` feature has not been properly tested on \
+                         all supported platforms",
+               issue = "27745")]
+    pub unsafe fn arg<T: sealed_trait::VaArgSafe>(&mut self) -> T {
+        va_arg(self)
+    }
+
+    /// Copy the `va_list` at the current location.
+    #[unstable(feature = "c_variadic",
+               reason = "the `c_variadic` feature has not been properly tested on \
+                         all supported platforms",
+               issue = "27745")]
+    pub unsafe fn copy<F, R>(&mut self, f: F) -> R
+            where F: for<'copy> FnOnce(VaList<'copy>) -> R {
+        #[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
+                      not(target_arch = "x86_64")),
+                  windows))]
+        let mut ap = va_copy(self);
+        #[cfg(all(any(target_arch = "aarch64", target_arch = "powerpc", target_arch = "x86_64"),
+                  not(windows)))]
+        let mut ap_inner = va_copy(self);
+        #[cfg(all(any(target_arch = "aarch64", target_arch = "powerpc", target_arch = "x86_64"),
+                  not(windows)))]
+        let mut ap = VaList(&mut ap_inner);
+        let ret = f(VaList(ap.0));
+        va_end(&mut ap);
+        ret
+    }
+}
+
+#[cfg(not(stage0))]
+extern "rust-intrinsic" {
+    /// Destroy the arglist `ap` after initialization with `va_start` or
+    /// `va_copy`.
+    fn va_end(ap: &mut VaList);
+
+    /// Copy the current location of arglist `src` to the arglist `dst`.
+    #[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
+                  not(target_arch = "x86_64")),
+              windows))]
+    fn va_copy<'a>(src: &VaList<'a>) -> VaList<'a>;
+    #[cfg(all(any(target_arch = "aarch64", target_arch = "powerpc", target_arch = "x86_64"),
+              not(windows)))]
+    fn va_copy(src: &VaList) -> VaListImpl;
+
+    /// Loads an argument of type `T` from the `va_list` `ap` and increment the
+    /// argument `ap` points to.
+    fn va_arg<T: sealed_trait::VaArgSafe>(ap: &mut VaList) -> T;
+}

src/librustc/middle/lang_items.rs

@@ -297,6 +297,7 @@ language_item_table! {
     IndexMutTraitLangItem,       "index_mut",          index_mut_trait,         Target::Trait;
 
     UnsafeCellTypeLangItem,      "unsafe_cell",        unsafe_cell_type,        Target::Struct;
+    VaListTypeLangItem,          "va_list",            va_list,                 Target::Struct;
 
     DerefTraitLangItem,          "deref",              deref_trait,             Target::Trait;
     DerefMutTraitLangItem,       "deref_mut",          deref_mut_trait,         Target::Trait;

src/librustc_codegen_llvm/context.rs

@@ -723,17 +723,17 @@ impl IntrinsicDeclarationMethods<'tcx> for CodegenCx<'b, 'tcx> {
         ifn!("llvm.bitreverse.i64", fn(t_i64) -> t_i64);
         ifn!("llvm.bitreverse.i128", fn(t_i128) -> t_i128);
 
-    ifn!("llvm.fshl.i8", fn(t_i8, t_i8, t_i8) -> t_i8);
-    ifn!("llvm.fshl.i16", fn(t_i16, t_i16, t_i16) -> t_i16);
-    ifn!("llvm.fshl.i32", fn(t_i32, t_i32, t_i32) -> t_i32);
-    ifn!("llvm.fshl.i64", fn(t_i64, t_i64, t_i64) -> t_i64);
-    ifn!("llvm.fshl.i128", fn(t_i128, t_i128, t_i128) -> t_i128);
-
-    ifn!("llvm.fshr.i8", fn(t_i8, t_i8, t_i8) -> t_i8);
-    ifn!("llvm.fshr.i16", fn(t_i16, t_i16, t_i16) -> t_i16);
-    ifn!("llvm.fshr.i32", fn(t_i32, t_i32, t_i32) -> t_i32);
-    ifn!("llvm.fshr.i64", fn(t_i64, t_i64, t_i64) -> t_i64);
-    ifn!("llvm.fshr.i128", fn(t_i128, t_i128, t_i128) -> t_i128);
+        ifn!("llvm.fshl.i8", fn(t_i8, t_i8, t_i8) -> t_i8);
+        ifn!("llvm.fshl.i16", fn(t_i16, t_i16, t_i16) -> t_i16);
+        ifn!("llvm.fshl.i32", fn(t_i32, t_i32, t_i32) -> t_i32);
+        ifn!("llvm.fshl.i64", fn(t_i64, t_i64, t_i64) -> t_i64);
+        ifn!("llvm.fshl.i128", fn(t_i128, t_i128, t_i128) -> t_i128);
+
+        ifn!("llvm.fshr.i8", fn(t_i8, t_i8, t_i8) -> t_i8);
+        ifn!("llvm.fshr.i16", fn(t_i16, t_i16, t_i16) -> t_i16);
+        ifn!("llvm.fshr.i32", fn(t_i32, t_i32, t_i32) -> t_i32);
+        ifn!("llvm.fshr.i64", fn(t_i64, t_i64, t_i64) -> t_i64);
+        ifn!("llvm.fshr.i128", fn(t_i128, t_i128, t_i128) -> t_i128);
 
         ifn!("llvm.sadd.with.overflow.i8", fn(t_i8, t_i8) -> mk_struct!{t_i8, i1});
         ifn!("llvm.sadd.with.overflow.i16", fn(t_i16, t_i16) -> mk_struct!{t_i16, i1});
@@ -783,6 +783,11 @@ impl IntrinsicDeclarationMethods<'tcx> for CodegenCx<'b, 'tcx> {
         ifn!("llvm.assume", fn(i1) -> void);
         ifn!("llvm.prefetch", fn(i8p, t_i32, t_i32, t_i32) -> void);
 
+        // variadic intrinsics
+        ifn!("llvm.va_start", fn(i8p) -> void);
+        ifn!("llvm.va_end", fn(i8p) -> void);
+        ifn!("llvm.va_copy", fn(i8p, i8p) -> void);
+
         if self.sess().opts.debuginfo != DebugInfo::None {
             ifn!("llvm.dbg.declare", fn(self.type_metadata(), self.type_metadata()) -> void);
             ifn!("llvm.dbg.value", fn(self.type_metadata(), t_i64, self.type_metadata()) -> void);

src/librustc_codegen_llvm/intrinsic.rs

@@ -24,13 +24,14 @@ use context::CodegenCx;
 use type_::Type;
 use type_of::LayoutLlvmExt;
 use rustc::ty::{self, Ty};
-use rustc::ty::layout::{LayoutOf, HasTyCtxt};
+use rustc::ty::layout::{self, LayoutOf, HasTyCtxt, Primitive};
 use rustc_codegen_ssa::common::TypeKind;
 use rustc::hir;
-use syntax::ast;
+use syntax::ast::{self, FloatTy};
 use syntax::symbol::Symbol;
 use builder::Builder;
 use value::Value;
+use va_arg::emit_va_arg;
 
 use rustc_codegen_ssa::traits::*;
 
@@ -146,6 +147,59 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
                 let tp_ty = substs.type_at(0);
                 self.cx().const_usize(self.cx().size_of(tp_ty).bytes())
             }
+            func @ "va_start" | func @ "va_end" => {
+                let va_list = match (tcx.lang_items().va_list(), &result.layout.ty.sty) {
+                    (Some(did), ty::Adt(def, _)) if def.did == did => args[0].immediate(),
+                    (Some(_), _) => self.load(args[0].immediate(),
+                                              tcx.data_layout.pointer_align.abi),
+                    (None, _) => bug!("va_list language item must be defined")
+                };
+                let intrinsic = self.cx().get_intrinsic(&format!("llvm.{}", func));
+                self.call(intrinsic, &[va_list], None)
+            }
+            "va_copy" => {
+                let va_list = match (tcx.lang_items().va_list(), &result.layout.ty.sty) {
+                    (Some(did), ty::Adt(def, _)) if def.did == did => args[0].immediate(),
+                    (Some(_), _)  => self.load(args[0].immediate(),
+                                               tcx.data_layout.pointer_align.abi),
+                    (None, _) => bug!("va_list language item must be defined")
+                };
+                let intrinsic = self.cx().get_intrinsic(&("llvm.va_copy"));
+                self.call(intrinsic, &[llresult, va_list], None);
+                return;
+            }
+            "va_arg" => {
+                match fn_ty.ret.layout.abi {
+                    layout::Abi::Scalar(ref scalar) => {
+                        match scalar.value {
+                            Primitive::Int(..) => {
+                                if self.cx().size_of(ret_ty).bytes() < 4 {
+                                    // va_arg should not be called on a integer type
+                                    // less than 4 bytes in length. If it is, promote
+                                    // the integer to a `i32` and truncate the result
+                                    // back to the smaller type.
+                                    let promoted_result = emit_va_arg(self, args[0],
+                                                                      tcx.types.i32);
+                                    self.trunc(promoted_result, llret_ty)
+                                } else {
+                                    emit_va_arg(self, args[0], ret_ty)
+                                }
+                            }
+                            Primitive::Float(FloatTy::F64) |
+                            Primitive::Pointer => {
+                                emit_va_arg(self, args[0], ret_ty)
+                            }
+                            // `va_arg` should never be used with the return type f32.
+                            Primitive::Float(FloatTy::F32) => {
+                                bug!("the va_arg intrinsic does not work with `f32`")
+                            }
+                        }
+                    }
+                    _ => {
+                        bug!("the va_arg intrinsic does not work with non-scalar types")
+                    }
+                }
+            }
             "size_of_val" => {
                 let tp_ty = substs.type_at(0);
                 if let OperandValue::Pair(_, meta) = args[0].val {

src/librustc_codegen_llvm/lib.rs

@@ -127,6 +127,7 @@ mod mono_item;
 mod type_;
 mod type_of;
 mod value;
+mod va_arg;
 
 #[derive(Clone)]
 pub struct LlvmCodegenBackend(());