auto merge of #5726 : brson/rust/struct-return, r=brson

r? @nikomatsakis

This doesn't completely fix the x86 ABI for structs, but it does fix some cases. On linux, structs appear to be returned correctly now. On windows, structs are only returned by pointer when they are greater than 8 bytes. That scenario works now.

In the case where the struct is less than 8 bytes our generated code looks peculiar. When returning a pair of u16, C packs both variables into %eax to return them. Our generated code though expects to find one of the pair in %ax and the other in %dx. Similar for u8. I haven't looked into it yet.

There appears to also be struct passing problems on linux, where my `extern-pass-TwoU8s` and `extern-pass-TwoU16s` tests are failing.

20 files changed, 482 insertions, 157 deletions

diff --git a/src/libcore/rt/uv/net.rs b/src/libcore/rt/uv/net.rs
index 29ea36cd88b..4b9ff4504dd 100644
--- a/src/libcore/rt/uv/net.rs
+++ b/src/libcore/rt/uv/net.rs
@@ -356,7 +356,6 @@ impl NativeHandle<*uvll::uv_write_t> for WriteRequest {
 
 
 #[test]
-#[ignore(reason = "ffi struct issues")]
 fn connect_close() {
     do run_in_bare_thread() {
         let mut loop_ = Loop::new();
@@ -409,7 +408,6 @@ fn connect_read() {
 }
 
 #[test]
-#[ignore(reason = "ffi struct issues")]
 fn listen() {
     do run_in_bare_thread() {
         static MAX: int = 10;
diff --git a/src/librustc/lib/llvm.rs b/src/librustc/lib/llvm.rs
index b6d3fce7e75..06f7261040c 100644
--- a/src/librustc/lib/llvm.rs
+++ b/src/librustc/lib/llvm.rs
@@ -125,27 +125,25 @@ pub enum RealPredicate {
     RealPredicateTrue = 15,
 }
 
-// enum for the LLVM TypeKind type - must stay in sync with the def of
+// The LLVM TypeKind type - must stay in sync with the def of
 // LLVMTypeKind in llvm/include/llvm-c/Core.h
-#[deriving(Eq)]
-pub enum TypeKind {
-    Void      = 0,
-    Half      = 1,
-    Float     = 2,
-    Double    = 3,
-    X86_FP80  = 4,
-    FP128     = 5,
-    PPC_FP128 = 6,
-    Label     = 7,
-    Integer   = 8,
-    Function  = 9,
-    Struct    = 10,
-    Array     = 11,
-    Pointer   = 12,
-    Vector    = 13,
-    Metadata  = 14,
-    X86_MMX   = 15
-}
+pub type TypeKind = u32;
+pub static Void: TypeKind      = 0;
+pub static Half: TypeKind      = 1;
+pub static Float: TypeKind     = 2;
+pub static Double: TypeKind    = 3;
+pub static X86_FP80: TypeKind  = 4;
+pub static FP128: TypeKind     = 5;
+pub static PPC_FP128: TypeKind = 6;
+pub static Label: TypeKind     = 7;
+pub static Integer: TypeKind   = 8;
+pub static Function: TypeKind  = 9;
+pub static Struct: TypeKind    = 10;
+pub static Array: TypeKind     = 11;
+pub static Pointer: TypeKind   = 12;
+pub static Vector: TypeKind    = 13;
+pub static Metadata: TypeKind  = 14;
+pub static X86_MMX: TypeKind   = 15;
 
 pub enum AtomicBinOp {
     Xchg = 0,
@@ -1582,7 +1580,8 @@ pub fn type_to_str_inner(names: @TypeNames, +outer0: &[TypeRef], ty: TypeRef)
           }
           Vector => return @"Vector",
           Metadata => return @"Metadata",
-          X86_MMX => return @"X86_MMAX"
+          X86_MMX => return @"X86_MMAX",
+          _ => fail!()
         }
     }
 }
diff --git a/src/librustc/middle/trans/cabi.rs b/src/librustc/middle/trans/cabi.rs
index 7e159ef6062..60b502873e2 100644
--- a/src/librustc/middle/trans/cabi.rs
+++ b/src/librustc/middle/trans/cabi.rs
@@ -180,37 +180,3 @@ pub impl FnType {
         Ret(bcx, llretval);
     }
 }
-
-enum LLVM_ABIInfo { LLVM_ABIInfo }
-
-impl ABIInfo for LLVM_ABIInfo {
-    fn compute_info(&self,
-                    atys: &[TypeRef],
-                    rty: TypeRef,
-                    _ret_def: bool) -> FnType {
-        let arg_tys = do atys.map |a| {
-            LLVMType { cast: false, ty: *a }
-        };
-        let ret_ty = LLVMType {
-            cast: false,
-            ty: rty
-        };
-        let attrs = do atys.map |_| {
-            option::None
-        };
-        let sret = false;
-
-        return FnType {
-            arg_tys: arg_tys,
-            ret_ty: ret_ty,
-            attrs: attrs,
-            sret: sret
-        };
-    }
-}
-
-pub fn llvm_abi_info() -> @ABIInfo {
-    return @LLVM_ABIInfo as @ABIInfo;
-}
-
-
diff --git a/src/librustc/middle/trans/cabi_mips.rs b/src/librustc/middle/trans/cabi_mips.rs
index ce37455560b..9a1c95e5184 100644
--- a/src/librustc/middle/trans/cabi_mips.rs
+++ b/src/librustc/middle/trans/cabi_mips.rs
@@ -227,6 +227,6 @@ impl ABIInfo for MIPS_ABIInfo {
     }
 }
 
-pub fn mips_abi_info() -> @ABIInfo {
+pub fn abi_info() -> @ABIInfo {
     return @MIPS_ABIInfo as @ABIInfo;
 }
diff --git a/src/librustc/middle/trans/cabi_x86.rs b/src/librustc/middle/trans/cabi_x86.rs
new file mode 100644
index 00000000000..a549f912171
--- /dev/null
+++ b/src/librustc/middle/trans/cabi_x86.rs
@@ -0,0 +1,77 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use driver::session::os_win32;
+use core::option::*;
+use lib::llvm::*;
+use lib::llvm::llvm::*;
+use super::cabi::*;
+use super::common::*;
+use super::machine::*;
+
+struct X86_ABIInfo {
+    ccx: @CrateContext
+}
+
+impl ABIInfo for X86_ABIInfo {
+    fn compute_info(&self,
+                    atys: &[TypeRef],
+                    rty: TypeRef,
+                    ret_def: bool) -> FnType {
+        let mut arg_tys = do atys.map |a| {
+            LLVMType { cast: false, ty: *a }
+        };
+        let mut ret_ty = LLVMType {
+            cast: false,
+            ty: rty
+        };
+        let mut attrs = do atys.map |_| {
+            None
+        };
+
+        // Rules for returning structs taken from
+        // http://www.angelcode.com/dev/callconv/callconv.html
+        let sret = {
+            let returning_a_struct = unsafe { LLVMGetTypeKind(rty) == Struct && ret_def };
+            let big_struct = if self.ccx.sess.targ_cfg.os != os_win32 {
+                true
+            } else {
+                llsize_of_alloc(self.ccx, rty) > 8
+            };
+            returning_a_struct && big_struct
+        };
+
+        if sret {
+            let ret_ptr_ty = LLVMType {
+                cast: false,
+                ty: T_ptr(ret_ty.ty)
+            };
+            arg_tys = ~[ret_ptr_ty] + arg_tys;
+            attrs = ~[Some(StructRetAttribute)] + attrs;
+            ret_ty = LLVMType {
+                cast: false,
+                ty: T_void(),
+            };
+        }
+
+        return FnType {
+            arg_tys: arg_tys,
+            ret_ty: ret_ty,
+            attrs: attrs,
+            sret: sret
+        };
+    }
+}
+
+pub fn abi_info(ccx: @CrateContext) -> @ABIInfo {
+    return @X86_ABIInfo {
+        ccx: ccx
+    } as @ABIInfo;
+}
diff --git a/src/librustc/middle/trans/cabi_x86_64.rs b/src/librustc/middle/trans/cabi_x86_64.rs
index fa85588cb0f..31ac4534462 100644
--- a/src/librustc/middle/trans/cabi_x86_64.rs
+++ b/src/librustc/middle/trans/cabi_x86_64.rs
@@ -410,6 +410,6 @@ impl ABIInfo for X86_64_ABIInfo {
     }
 }
 
-pub fn x86_64_abi_info() -> @ABIInfo {
+pub fn abi_info() -> @ABIInfo {
     return @X86_64_ABIInfo as @ABIInfo;
 }
diff --git a/src/librustc/middle/trans/foreign.rs b/src/librustc/middle/trans/foreign.rs
index 387caa4d8d3..1037a4c0710 100644
--- a/src/librustc/middle/trans/foreign.rs
+++ b/src/librustc/middle/trans/foreign.rs
@@ -16,9 +16,10 @@ use lib::llvm::{TypeRef, ValueRef};
 use lib;
 use middle::trans::base::*;
 use middle::trans::cabi;
-use middle::trans::cabi_x86_64::*;
+use middle::trans::cabi_x86;
+use middle::trans::cabi_x86_64;
 use middle::trans::cabi_arm;
-use middle::trans::cabi_mips::*;
+use middle::trans::cabi_mips;
 use middle::trans::build::*;
 use middle::trans::callee::*;
 use middle::trans::common::*;
@@ -42,12 +43,12 @@ use syntax::abi::{Architecture, X86, X86_64, Arm, Mips};
 use syntax::abi::{RustIntrinsic, Rust, Stdcall, Fastcall,
                   Cdecl, Aapcs, C};
 
-fn abi_info(arch: Architecture) -> @cabi::ABIInfo {
-    return match arch {
-        X86_64 => x86_64_abi_info(),
+fn abi_info(ccx: @CrateContext) -> @cabi::ABIInfo {
+    return match ccx.sess.targ_cfg.arch {
+        X86 => cabi_x86::abi_info(ccx),
+        X86_64 => cabi_x86_64::abi_info(),
         Arm => cabi_arm::abi_info(),
-        Mips => mips_abi_info(),
-        X86 => cabi::llvm_abi_info()
+        Mips => cabi_mips::abi_info(),
     }
 }
 
@@ -112,7 +113,7 @@ fn shim_types(ccx: @CrateContext, id: ast::node_id) -> ShimTypes {
         !ty::type_is_bot(fn_sig.output) &&
         !ty::type_is_nil(fn_sig.output);
     let fn_ty =
-        abi_info(ccx.sess.targ_cfg.arch).compute_info(
+        abi_info(ccx).compute_info(
             llsig.llarg_tys,
             llsig.llret_ty,
             ret_def);
diff --git a/src/librustc/rustc.rc b/src/librustc/rustc.rc
index d1dbb48ba08..3fbe1b96ef7 100644
--- a/src/librustc/rustc.rc
+++ b/src/librustc/rustc.rc
@@ -69,6 +69,7 @@ pub mod middle {
         pub mod tvec;
         pub mod meth;
         pub mod cabi;
+        pub mod cabi_x86;
         pub mod cabi_x86_64;
         pub mod cabi_arm;
         pub mod cabi_mips;
diff --git a/src/rt/rust_builtin.cpp b/src/rt/rust_builtin.cpp
index 3c6cc9d9245..475c030e8f2 100644
--- a/src/rt/rust_builtin.cpp
+++ b/src/rt/rust_builtin.cpp
@@ -589,50 +589,6 @@ rust_log_console_off() {
     log_console_off(task->kernel->env);
 }
 
-extern "C" CDECL lock_and_signal *
-rust_dbg_lock_create() {
-    return new lock_and_signal();
-}
-
-extern "C" CDECL void
-rust_dbg_lock_destroy(lock_and_signal *lock) {
-    assert(lock);
-    delete lock;
-}
-
-extern "C" CDECL void
-rust_dbg_lock_lock(lock_and_signal *lock) {
-    assert(lock);
-    lock->lock();
-}
-
-extern "C" CDECL void
-rust_dbg_lock_unlock(lock_and_signal *lock) {
-    assert(lock);
-    lock->unlock();
-}
-
-extern "C" CDECL void
-rust_dbg_lock_wait(lock_and_signal *lock) {
-    assert(lock);
-    lock->wait();
-}
-
-extern "C" CDECL void
-rust_dbg_lock_signal(lock_and_signal *lock) {
-    assert(lock);
-    lock->signal();
-}
-
-typedef void *(*dbg_callback)(void*);
-
-extern "C" CDECL void *
-rust_dbg_call(dbg_callback cb, void *data) {
-    return cb(data);
-}
-
-extern "C" CDECL void rust_dbg_do_nothing() { }
-
 extern "C" CDECL void
 rust_dbg_breakpoint() {
     BREAKPOINT_AWESOME;
@@ -844,48 +800,6 @@ rust_readdir() {
 
 #endif
 
-// These functions are used in the unit tests for C ABI calls.
-
-extern "C" CDECL uint32_t
-rust_dbg_extern_identity_u32(uint32_t u) {
-    return u;
-}
-
-extern "C" CDECL uint64_t
-rust_dbg_extern_identity_u64(uint64_t u) {
-    return u;
-}
-
-struct TwoU64s {
-    uint64_t one;
-    uint64_t two;
-};
-
-extern "C" CDECL TwoU64s
-rust_dbg_extern_identity_TwoU64s(TwoU64s u) {
-    return u;
-}
-
-struct TwoDoubles {
-    double one;
-    double two;
-};
-
-extern "C" CDECL TwoDoubles
-rust_dbg_extern_identity_TwoDoubles(TwoDoubles u) {
-    return u;
-}
-
-extern "C" CDECL double
-rust_dbg_extern_identity_double(double u) {
-    return u;
-}
-
-extern "C" CDECL char
-rust_dbg_extern_identity_u8(char u) {
-    return u;
-}
-
 extern "C" rust_env*
 rust_get_rt_env() {
     rust_task *task = rust_get_current_task();
diff --git a/src/rt/rust_test_helpers.cpp b/src/rt/rust_test_helpers.cpp
new file mode 100644
index 00000000000..64966bd3454
--- /dev/null
+++ b/src/rt/rust_test_helpers.cpp
@@ -0,0 +1,167 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Helper functions used only in tests
+
+#include "rust_sched_loop.h"
+#include "rust_task.h"
+#include "rust_util.h"
+#include "rust_scheduler.h"
+#include "sync/timer.h"
+#include "sync/rust_thread.h"
+#include "rust_abi.h"
+
+// These functions are used in the unit tests for C ABI calls.
+
+extern "C" CDECL uint32_t
+rust_dbg_extern_identity_u32(uint32_t u) {
+    return u;
+}
+
+extern "C" CDECL uint64_t
+rust_dbg_extern_identity_u64(uint64_t u) {
+    return u;
+}
+
+extern "C" CDECL double
+rust_dbg_extern_identity_double(double u) {
+    return u;
+}
+
+extern "C" CDECL char
+rust_dbg_extern_identity_u8(char u) {
+    return u;
+}
+
+extern "C" CDECL lock_and_signal *
+rust_dbg_lock_create() {
+    return new lock_and_signal();
+}
+
+extern "C" CDECL void
+rust_dbg_lock_destroy(lock_and_signal *lock) {
+    assert(lock);
+    delete lock;
+}
+
+extern "C" CDECL void
+rust_dbg_lock_lock(lock_and_signal *lock) {
+    assert(lock);
+    lock->lock();
+}
+
+extern "C" CDECL void
+rust_dbg_lock_unlock(lock_and_signal *lock) {
+    assert(lock);
+    lock->unlock();
+}
+
+extern "C" CDECL void
+rust_dbg_lock_wait(lock_and_signal *lock) {
+    assert(lock);
+    lock->wait();
+}
+
+extern "C" CDECL void
+rust_dbg_lock_signal(lock_and_signal *lock) {
+    assert(lock);
+    lock->signal();
+}
+
+typedef void *(*dbg_callback)(void*);
+
+extern "C" CDECL void *
+rust_dbg_call(dbg_callback cb, void *data) {
+    return cb(data);
+}
+
+extern "C" CDECL void rust_dbg_do_nothing() { }
+
+struct TwoU8s {
+    uint8_t one;
+    uint8_t two;
+};
+
+extern "C" CDECL TwoU8s
+rust_dbg_extern_return_TwoU8s() {
+    struct TwoU8s s;
+    s.one = 10;
+    s.two = 20;
+    return s;
+}
+
+extern "C" CDECL TwoU8s
+rust_dbg_extern_identity_TwoU8s(TwoU8s u) {
+    return u;
+}
+
+struct TwoU16s {
+    uint16_t one;
+    uint16_t two;
+};
+
+extern "C" CDECL TwoU16s
+rust_dbg_extern_return_TwoU16s() {
+    struct TwoU16s s;
+    s.one = 10;
+    s.two = 20;
+    return s;
+}
+
+extern "C" CDECL TwoU16s
+rust_dbg_extern_identity_TwoU16s(TwoU16s u) {
+    return u;
+}
+
+struct TwoU32s {
+    uint32_t one;
+    uint32_t two;
+};
+
+extern "C" CDECL TwoU32s
+rust_dbg_extern_return_TwoU32s() {
+    struct TwoU32s s;
+    s.one = 10;
+    s.two = 20;
+    return s;
+}
+
+extern "C" CDECL TwoU32s
+rust_dbg_extern_identity_TwoU32s(TwoU32s u) {
+    return u;
+}
+
+struct TwoU64s {
+    uint64_t one;
+    uint64_t two;
+};
+
+extern "C" CDECL TwoU64s
+rust_dbg_extern_return_TwoU64s() {
+    struct TwoU64s s;
+    s.one = 10;
+    s.two = 20;
+    return s;
+}
+
+extern "C" CDECL TwoU64s
+rust_dbg_extern_identity_TwoU64s(TwoU64s u) {
+    return u;
+}
+
+struct TwoDoubles {
+    double one;
+    double two;
+};
+
+extern "C" CDECL TwoDoubles
+rust_dbg_extern_identity_TwoDoubles(TwoDoubles u) {
+    return u;
+}
diff --git a/src/rt/rustrt.def.in b/src/rt/rustrt.def.in
index 73dbe661d3f..f63e3f53a7c 100644
--- a/src/rt/rustrt.def.in
+++ b/src/rt/rustrt.def.in
@@ -198,8 +198,15 @@ rust_readdir
 rust_opendir
 rust_dbg_extern_identity_u32
 rust_dbg_extern_identity_u64
+rust_dbg_extern_identity_TwoU8s
+rust_dbg_extern_identity_TwoU16s
+rust_dbg_extern_identity_TwoU32s
 rust_dbg_extern_identity_TwoU64s
 rust_dbg_extern_identity_TwoDoubles
+rust_dbg_extern_return_TwoU8s
+rust_dbg_extern_return_TwoU16s
+rust_dbg_extern_return_TwoU32s
+rust_dbg_extern_return_TwoU64s
 rust_dbg_extern_identity_double
 rust_dbg_extern_identity_u8
 rust_get_rt_env
@@ -214,4 +221,3 @@ rust_uv_free_ip6_addr
 rust_call_nullary_fn
 rust_initialize_global_state
 
-
diff --git a/src/test/run-pass/extern-pass-TwoU16s.rs b/src/test/run-pass/extern-pass-TwoU16s.rs
new file mode 100644
index 00000000000..f0343c4d2a2
--- /dev/null
+++ b/src/test/run-pass/extern-pass-TwoU16s.rs
@@ -0,0 +1,32 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test a foreign function that accepts and returns a struct
+// by value.
+
+// xfail-test #5744
+
+#[deriving(Eq)]
+struct TwoU16s {
+    one: u16, two: u16
+}
+
+pub extern {
+    pub fn rust_dbg_extern_identity_TwoU16s(v: TwoU16s) -> TwoU16s;
+}
+
+pub fn main() {
+    unsafe {
+        let x = TwoU16s {one: 22, two: 23};
+        let y = rust_dbg_extern_identity_TwoU16s(x);
+        assert!(x == y);
+    }
+}
+
diff --git a/src/test/run-pass/extern-pass-TwoU32s.rs b/src/test/run-pass/extern-pass-TwoU32s.rs
new file mode 100644
index 00000000000..16d14a96cfe
--- /dev/null
+++ b/src/test/run-pass/extern-pass-TwoU32s.rs
@@ -0,0 +1,30 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test a foreign function that accepts and returns a struct
+// by value.
+
+#[deriving(Eq)]
+struct TwoU32s {
+    one: u32, two: u32
+}
+
+pub extern {
+    pub fn rust_dbg_extern_identity_TwoU32s(v: TwoU32s) -> TwoU32s;
+}
+
+pub fn main() {
+    unsafe {
+        let x = TwoU32s {one: 22, two: 23};
+        let y = rust_dbg_extern_identity_TwoU32s(x);
+        assert!(x == y);
+    }
+}
+
diff --git a/src/test/run-pass/extern-pass-TwoU64s-ref.rs b/src/test/run-pass/extern-pass-TwoU64s-ref.rs
index 87bec86d8de..56d3f8ebbff 100644
--- a/src/test/run-pass/extern-pass-TwoU64s-ref.rs
+++ b/src/test/run-pass/extern-pass-TwoU64s-ref.rs
@@ -10,8 +10,6 @@
 
 // Test that we ignore modes when calling extern functions.
 
-// xfail-test --- broken on 32-bit ABIs! (#5347)
-
 #[deriving(Eq)]
 struct TwoU64s {
     one: u64, two: u64
diff --git a/src/test/run-pass/extern-pass-TwoU64s.rs b/src/test/run-pass/extern-pass-TwoU64s.rs
index fb91d5495e1..eb2e3b1158f 100644
--- a/src/test/run-pass/extern-pass-TwoU64s.rs
+++ b/src/test/run-pass/extern-pass-TwoU64s.rs
@@ -11,7 +11,7 @@
 // Test a foreign function that accepts and returns a struct
 // by value.
 
-// xfail-test --- broken on 32-bit ABIs! (#5347)
+// xfail-fast This works standalone on windows but not with check-fast. don't know why
 
 #[deriving(Eq)]
 struct TwoU64s {
diff --git a/src/test/run-pass/extern-pass-TwoU8s.rs b/src/test/run-pass/extern-pass-TwoU8s.rs
new file mode 100644
index 00000000000..213e9a68a7f
--- /dev/null
+++ b/src/test/run-pass/extern-pass-TwoU8s.rs
@@ -0,0 +1,32 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test a foreign function that accepts and returns a struct
+// by value.
+
+// xfail-test #5744
+
+#[deriving(Eq)]
+struct TwoU8s {
+    one: u8, two: u8
+}
+
+pub extern {
+    pub fn rust_dbg_extern_identity_TwoU8s(v: TwoU8s) -> TwoU8s;
+}
+
+pub fn main() {
+    unsafe {
+        let x = TwoU8s {one: 22, two: 23};
+        let y = rust_dbg_extern_identity_TwoU8s(x);
+        assert!(x == y);
+    }
+}
+
diff --git a/src/test/run-pass/extern-return-TwoU16s.rs b/src/test/run-pass/extern-return-TwoU16s.rs
new file mode 100644
index 00000000000..0ea649a65b0
--- /dev/null
+++ b/src/test/run-pass/extern-return-TwoU16s.rs
@@ -0,0 +1,27 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// xfail-win32 #5745
+
+struct TwoU16s {
+    one: u16, two: u16
+}
+
+pub extern {
+    pub fn rust_dbg_extern_return_TwoU16s() -> TwoU16s;
+}
+
+pub fn main() {
+    unsafe {
+        let y = rust_dbg_extern_return_TwoU16s();
+        assert!(y.one == 10);
+        assert!(y.two == 20);
+    }
+}
diff --git a/src/test/run-pass/extern-return-TwoU32s.rs b/src/test/run-pass/extern-return-TwoU32s.rs
new file mode 100644
index 00000000000..9e374687855
--- /dev/null
+++ b/src/test/run-pass/extern-return-TwoU32s.rs
@@ -0,0 +1,25 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct TwoU32s {
+    one: u32, two: u32
+}
+
+pub extern {
+    pub fn rust_dbg_extern_return_TwoU32s() -> TwoU32s;
+}
+
+pub fn main() {
+    unsafe {
+        let y = rust_dbg_extern_return_TwoU32s();
+        assert!(y.one == 10);
+        assert!(y.two == 20);
+    }
+}
diff --git a/src/test/run-pass/extern-return-TwoU64s.rs b/src/test/run-pass/extern-return-TwoU64s.rs
new file mode 100644
index 00000000000..250d3b8f562
--- /dev/null
+++ b/src/test/run-pass/extern-return-TwoU64s.rs
@@ -0,0 +1,25 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct TwoU64s {
+    one: u64, two: u64
+}
+
+pub extern {
+    pub fn rust_dbg_extern_return_TwoU64s() -> TwoU64s;
+}
+
+pub fn main() {
+    unsafe {
+        let y = rust_dbg_extern_return_TwoU64s();
+        assert!(y.one == 10);
+        assert!(y.two == 20);
+    }
+}
diff --git a/src/test/run-pass/extern-return-TwoU8s.rs b/src/test/run-pass/extern-return-TwoU8s.rs
new file mode 100644
index 00000000000..9007d12a451
--- /dev/null
+++ b/src/test/run-pass/extern-return-TwoU8s.rs
@@ -0,0 +1,27 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// xfail-win32 #5745
+
+struct TwoU8s {
+    one: u8, two: u8
+}
+
+pub extern {
+    pub fn rust_dbg_extern_return_TwoU8s() -> TwoU8s;
+}
+
+pub fn main() {
+    unsafe {
+        let y = rust_dbg_extern_return_TwoU8s();
+        assert!(y.one == 10);
+        assert!(y.two == 20);
+    }
+}