Auto merge of #44906 - dkl:main-signature, r=nagisa

Fix native main() signature on 64bit

Hello,

in LLVM-IR produced by rustc on x86_64-linux-gnu, the native main() function had incorrect types for the function result and argc parameter: i64, while it should be i32 (really c_int). See also #20064, #29633.

So I've attempted a fix here. I tested it by checking the LLVM IR produced with --target x86_64-unknown-linux-gnu and i686-unknown-linux-gnu. Also I tried running the tests (`./x.py test`), however I'm getting two failures with and without the patch, which I'm guessing is unrelated.

src/librustc_back/target/aarch64_apple_ios.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
         llvm_target: "arm64-apple-ios".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:o-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
         target_os: "ios".to_string(),

src/librustc_back/target/aarch64_linux_android.rs

@@ -24,6 +24,7 @@ pub fn target() -> TargetResult {
         llvm_target: "aarch64-linux-android".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
         target_os: "android".to_string(),

src/librustc_back/target/aarch64_unknown_freebsd.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "aarch64-unknown-freebsd".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
         target_os: "freebsd".to_string(),

src/librustc_back/target/aarch64_unknown_fuchsia.rs

@@ -19,6 +19,7 @@ pub fn target() -> TargetResult {
         llvm_target: "aarch64-unknown-fuchsia".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
         target_os: "fuchsia".to_string(),

src/librustc_back/target/aarch64_unknown_linux_gnu.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "aarch64-unknown-linux-gnu".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         target_env: "gnu".to_string(),
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),

src/librustc_back/target/aarch64_unknown_linux_musl.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "aarch64-unknown-linux-musl".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         target_env: "musl".to_string(),
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),

src/librustc_back/target/arm_linux_androideabi.rs

@@ -21,6 +21,7 @@ pub fn target() -> TargetResult {
         llvm_target: "arm-linux-androideabi".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "android".to_string(),

src/librustc_back/target/arm_unknown_linux_gnueabi.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
         llvm_target: "arm-unknown-linux-gnueabi".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/arm_unknown_linux_gnueabihf.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
         llvm_target: "arm-unknown-linux-gnueabihf".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/arm_unknown_linux_musleabi.rs

@@ -25,6 +25,7 @@ pub fn target() -> TargetResult {
         llvm_target: "arm-unknown-linux-gnueabi".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/arm_unknown_linux_musleabihf.rs

@@ -25,6 +25,7 @@ pub fn target() -> TargetResult {
         llvm_target: "arm-unknown-linux-gnueabihf".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/armv5te_unknown_linux_gnueabi.rs

@@ -17,6 +17,7 @@ pub fn target() -> TargetResult {
         llvm_target: "armv5te-unknown-linux-gnueabi".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/armv7_apple_ios.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
         llvm_target: "armv7-apple-ios".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:o-p:32:32-f64:32:64-v64:32:64-v128:32:128-a:0:32-n32-S32".to_string(),
         arch: "arm".to_string(),
         target_os: "ios".to_string(),

src/librustc_back/target/armv7_linux_androideabi.rs

@@ -25,6 +25,7 @@ pub fn target() -> TargetResult {
         llvm_target: "armv7-none-linux-android".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "android".to_string(),

src/librustc_back/target/armv7_unknown_linux_gnueabihf.rs

@@ -17,6 +17,7 @@ pub fn target() -> TargetResult {
         llvm_target: "armv7-unknown-linux-gnueabihf".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/armv7_unknown_linux_musleabihf.rs

@@ -26,6 +26,7 @@ pub fn target() -> TargetResult {
         llvm_target: "armv7-unknown-linux-gnueabihf".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/armv7s_apple_ios.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
         llvm_target: "armv7s-apple-ios".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:o-p:32:32-f64:32:64-v64:32:64-v128:32:128-a:0:32-n32-S32".to_string(),
         arch: "arm".to_string(),
         target_os: "ios".to_string(),

src/librustc_back/target/asmjs_unknown_emscripten.rs

@@ -38,6 +38,7 @@ pub fn target() -> Result<Target, String> {
         llvm_target: "asmjs-unknown-emscripten".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         target_os: "emscripten".to_string(),
         target_env: "".to_string(),
         target_vendor: "unknown".to_string(),

src/librustc_back/target/i386_apple_ios.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
         llvm_target: "i386-apple-ios".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:o-p:32:32-f64:32:64-f80:128-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "ios".to_string(),

src/librustc_back/target/i686_apple_darwin.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "i686-apple-darwin".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:o-p:32:32-f64:32:64-f80:128-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "macos".to_string(),

src/librustc_back/target/i686_linux_android.rs

@@ -28,6 +28,7 @@ pub fn target() -> TargetResult {
         llvm_target: "i686-linux-android".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "android".to_string(),

src/librustc_back/target/i686_pc_windows_gnu.rs

@@ -26,6 +26,7 @@ pub fn target() -> TargetResult {
         llvm_target: "i686-pc-windows-gnu".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32".to_string(),
         arch: "x86".to_string(),
         target_os: "windows".to_string(),

src/librustc_back/target/i686_pc_windows_msvc.rs

@@ -30,6 +30,7 @@ pub fn target() -> TargetResult {
         llvm_target: "i686-pc-windows-msvc".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32".to_string(),
         arch: "x86".to_string(),
         target_os: "windows".to_string(),

src/librustc_back/target/i686_unknown_dragonfly.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "i686-unknown-dragonfly".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "dragonfly".to_string(),

src/librustc_back/target/i686_unknown_freebsd.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "i686-unknown-freebsd".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "freebsd".to_string(),

src/librustc_back/target/i686_unknown_haiku.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "i686-unknown-haiku".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "haiku".to_string(),

src/librustc_back/target/i686_unknown_linux_gnu.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "i686-unknown-linux-gnu".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/i686_unknown_linux_musl.rs

@@ -37,6 +37,7 @@ pub fn target() -> TargetResult {
         llvm_target: "i686-unknown-linux-musl".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/i686_unknown_netbsd.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "i686-unknown-netbsdelf".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "netbsd".to_string(),

src/librustc_back/target/i686_unknown_openbsd.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "i686-unknown-openbsd".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "openbsd".to_string(),

src/librustc_back/target/le32_unknown_nacl.rs

@@ -39,6 +39,7 @@ pub fn target() -> TargetResult {
         llvm_target: "le32-unknown-nacl".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         target_os: "nacl".to_string(),
         target_env: "newlib".to_string(),
         target_vendor: "unknown".to_string(),

src/librustc_back/target/mips64_unknown_linux_gnuabi64.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
         llvm_target: "mips64-unknown-linux-gnuabi64".to_string(),
         target_endian: "big".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "E-m:e-i8:8:32-i16:16:32-i64:64-n32:64-S128".to_string(),
         arch: "mips64".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/mips64el_unknown_linux_gnuabi64.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
         llvm_target: "mips64el-unknown-linux-gnuabi64".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-n32:64-S128".to_string(),
         arch: "mips64".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/mips_unknown_linux_gnu.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
         llvm_target: "mips-unknown-linux-gnu".to_string(),
         target_endian: "big".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "E-m:m-p:32:32-i8:8:32-i16:16:32-i64:64-n32-S64".to_string(),
         arch: "mips".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/mips_unknown_linux_musl.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
         llvm_target: "mips-unknown-linux-musl".to_string(),
         target_endian: "big".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "E-m:m-p:32:32-i8:8:32-i16:16:32-i64:64-n32-S64".to_string(),
         arch: "mips".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/mips_unknown_linux_uclibc.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
         llvm_target: "mips-unknown-linux-uclibc".to_string(),
         target_endian: "big".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "E-m:m-p:32:32-i8:8:32-i16:16:32-i64:64-n32-S64".to_string(),
         arch: "mips".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/mipsel_unknown_linux_gnu.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
         llvm_target: "mipsel-unknown-linux-gnu".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:m-p:32:32-i8:8:32-i16:16:32-i64:64-n32-S64".to_string(),
         arch: "mips".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/mipsel_unknown_linux_musl.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
         llvm_target: "mipsel-unknown-linux-musl".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:m-p:32:32-i8:8:32-i16:16:32-i64:64-n32-S64".to_string(),
         arch: "mips".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/mipsel_unknown_linux_uclibc.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
         llvm_target: "mipsel-unknown-linux-uclibc".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:m-p:32:32-i8:8:32-i16:16:32-i64:64-n32-S64".to_string(),
         arch: "mips".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/mod.rs

@@ -239,6 +239,8 @@ pub struct Target {
     pub target_endian: String,
     /// String to use as the `target_pointer_width` `cfg` variable.
     pub target_pointer_width: String,
+    /// Width of c_int type
+    pub target_c_int_width: String,
     /// OS name to use for conditional compilation.
     pub target_os: String,
     /// Environment name to use for conditional compilation.
@@ -556,6 +558,7 @@ impl Target {
             llvm_target: get_req_field("llvm-target")?,
             target_endian: get_req_field("target-endian")?,
             target_pointer_width: get_req_field("target-pointer-width")?,
+            target_c_int_width: get_req_field("target-c-int-width")?,
             data_layout: get_req_field("data-layout")?,
             arch: get_req_field("arch")?,
             target_os: get_req_field("os")?,
@@ -860,6 +863,7 @@ impl ToJson for Target {
         target_val!(llvm_target);
         target_val!(target_endian);
         target_val!(target_pointer_width);
+        target_val!(target_c_int_width);
         target_val!(arch);
         target_val!(target_os, "os");
         target_val!(target_env, "env");

src/librustc_back/target/msp430_none_elf.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
         llvm_target: "msp430-none-elf".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "16".to_string(),
+        target_c_int_width: "16".to_string(),
         data_layout: "e-m:e-p:16:16-i32:16-i64:16-f32:16-f64:16-a:8-n8:16-S16".to_string(),
         arch: "msp430".to_string(),
         target_os: "none".to_string(),

src/librustc_back/target/powerpc64_unknown_linux_gnu.rs

@@ -28,6 +28,7 @@ pub fn target() -> TargetResult {
         llvm_target: "powerpc64-unknown-linux-gnu".to_string(),
         target_endian: "big".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "E-m:e-i64:64-n32:64".to_string(),
         arch: "powerpc64".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/powerpc64le_unknown_linux_gnu.rs

@@ -24,6 +24,7 @@ pub fn target() -> TargetResult {
         llvm_target: "powerpc64le-unknown-linux-gnu".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-n32:64".to_string(),
         arch: "powerpc64".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/powerpc_unknown_linux_gnu.rs

@@ -23,6 +23,7 @@ pub fn target() -> TargetResult {
         llvm_target: "powerpc-unknown-linux-gnu".to_string(),
         target_endian: "big".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "E-m:e-p:32:32-i64:64-n32".to_string(),
         arch: "powerpc".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/s390x_unknown_linux_gnu.rs

@@ -28,6 +28,7 @@ pub fn target() -> TargetResult {
         llvm_target: "s390x-unknown-linux-gnu".to_string(),
         target_endian: "big".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "E-m:e-i1:8:16-i8:8:16-i64:64-f128:64-a:8:16-n32:64".to_string(),
         arch: "s390x".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/sparc64_unknown_linux_gnu.rs

@@ -21,6 +21,7 @@ pub fn target() -> TargetResult {
         llvm_target: "sparc64-unknown-linux-gnu".to_string(),
         target_endian: "big".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "E-m:e-i64:64-n32:64-S128".to_string(),
         arch: "sparc64".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/sparc64_unknown_netbsd.rs

@@ -21,6 +21,7 @@ pub fn target() -> TargetResult {
         llvm_target: "sparc64-unknown-netbsd".to_string(),
         target_endian: "big".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "E-m:e-i64:64-n32:64-S128".to_string(),
         arch: "sparc64".to_string(),
         target_os: "netbsd".to_string(),

src/librustc_back/target/sparcv9_sun_solaris.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "sparcv9-sun-solaris".to_string(),
         target_endian: "big".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "E-m:e-i64:64-n32:64-S128".to_string(),
         // Use "sparc64" instead of "sparcv9" here, since the former is already
         // used widely in the source base.  If we ever needed ABI

src/librustc_back/target/thumbv6m_none_eabi.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
         llvm_target: "thumbv6m-none-eabi".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "none".to_string(),

src/librustc_back/target/thumbv7em_none_eabi.rs

@@ -27,6 +27,7 @@ pub fn target() -> TargetResult {
         llvm_target: "thumbv7em-none-eabi".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "none".to_string(),

src/librustc_back/target/thumbv7em_none_eabihf.rs

@@ -26,6 +26,7 @@ pub fn target() -> TargetResult {
         llvm_target: "thumbv7em-none-eabihf".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "none".to_string(),

src/librustc_back/target/thumbv7m_none_eabi.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
         llvm_target: "thumbv7m-none-eabi".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "none".to_string(),

src/librustc_back/target/wasm32_experimental_emscripten.rs

@@ -46,6 +46,7 @@ pub fn target() -> Result<Target, String> {
         llvm_target: "wasm32-unknown-unknown".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         target_os: "emscripten".to_string(),
         target_env: "".to_string(),
         target_vendor: "unknown".to_string(),

src/librustc_back/target/wasm32_unknown_emscripten.rs

@@ -42,6 +42,7 @@ pub fn target() -> Result<Target, String> {
         llvm_target: "asmjs-unknown-emscripten".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
         target_os: "emscripten".to_string(),
         target_env: "".to_string(),
         target_vendor: "unknown".to_string(),

src/librustc_back/target/x86_64_apple_darwin.rs

@@ -23,6 +23,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-apple-darwin".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:o-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "macos".to_string(),

src/librustc_back/target/x86_64_apple_ios.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-apple-ios".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:o-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "ios".to_string(),

src/librustc_back/target/x86_64_linux_android.rs

@@ -24,6 +24,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-linux-android".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "android".to_string(),

src/librustc_back/target/x86_64_pc_windows_gnu.rs

@@ -21,6 +21,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-pc-windows-gnu".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:w-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "windows".to_string(),

src/librustc_back/target/x86_64_pc_windows_msvc.rs

@@ -21,6 +21,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-pc-windows-msvc".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:w-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "windows".to_string(),

src/librustc_back/target/x86_64_rumprun_netbsd.rs

@@ -31,6 +31,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-rumprun-netbsd".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "netbsd".to_string(),

src/librustc_back/target/x86_64_sun_solaris.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-pc-solaris".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "solaris".to_string(),

src/librustc_back/target/x86_64_unknown_bitrig.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-unknown-bitrig".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "bitrig".to_string(),

src/librustc_back/target/x86_64_unknown_dragonfly.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-unknown-dragonfly".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "dragonfly".to_string(),

src/librustc_back/target/x86_64_unknown_freebsd.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-unknown-freebsd".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "freebsd".to_string(),

src/librustc_back/target/x86_64_unknown_fuchsia.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-unknown-fuchsia".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "fuchsia".to_string(),

src/librustc_back/target/x86_64_unknown_haiku.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-unknown-haiku".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "haiku".to_string(),

src/librustc_back/target/x86_64_unknown_l4re_uclibc.rs

@@ -20,6 +20,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-unknown-l4re-uclibc".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "l4re".to_string(),

src/librustc_back/target/x86_64_unknown_linux_gnu.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-unknown-linux-gnu".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/x86_64_unknown_linux_musl.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-unknown-linux-musl".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "linux".to_string(),

src/librustc_back/target/x86_64_unknown_netbsd.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-unknown-netbsd".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "netbsd".to_string(),

src/librustc_back/target/x86_64_unknown_openbsd.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-unknown-openbsd".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "openbsd".to_string(),

src/librustc_back/target/x86_64_unknown_redox.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
         llvm_target: "x86_64-unknown-redox".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "redox".to_string(),

src/librustc_trans/base.rs

@@ -77,7 +77,6 @@ use value::Value;
 use rustc::util::nodemap::{NodeSet, FxHashMap, FxHashSet, DefIdSet};
 use CrateInfo;
 
-use libc::c_uint;
 use std::any::Any;
 use std::cell::RefCell;
 use std::ffi::{CStr, CString};
@@ -692,7 +691,8 @@ fn maybe_create_entry_wrapper(ccx: &CrateContext) {
                        sp: Span,
                        rust_main: ValueRef,
                        use_start_lang_item: bool) {
-        let llfty = Type::func(&[ccx.isize_ty(), Type::i8p(ccx).ptr_to()], &ccx.isize_ty());
+        // Signature of native main(), corresponding to C's `int main(int, char **)`
+        let llfty = Type::func(&[Type::c_int(ccx), Type::i8p(ccx).ptr_to()], &Type::c_int(ccx));
 
         if declare::get_defined_value(ccx, "main").is_some() {
             // FIXME: We should be smart and show a better diagnostic here.
@@ -711,19 +711,27 @@ fn maybe_create_entry_wrapper(ccx: &CrateContext) {
 
         debuginfo::gdb::insert_reference_to_gdb_debug_scripts_section_global(ccx, &bld);
 
+        // Params from native main() used as args for rust start function
+        let param_argc = get_param(llfn, 0);
+        let param_argv = get_param(llfn, 1);
+        let arg_argc = bld.intcast(param_argc, ccx.isize_ty(), true);
+        let arg_argv = param_argv;
+
         let (start_fn, args) = if use_start_lang_item {
             let start_def_id = ccx.tcx().require_lang_item(StartFnLangItem);
             let start_instance = Instance::mono(ccx.tcx(), start_def_id);
             let start_fn = callee::get_fn(ccx, start_instance);
-            (start_fn, vec![bld.pointercast(rust_main, Type::i8p(ccx).ptr_to()), get_param(llfn, 0),
-                get_param(llfn, 1)])
+            (start_fn, vec![bld.pointercast(rust_main, Type::i8p(ccx).ptr_to()),
+                            arg_argc, arg_argv])
         } else {
             debug!("using user-defined start fn");
-            (rust_main, vec![get_param(llfn, 0 as c_uint), get_param(llfn, 1 as c_uint)])
+            (rust_main, vec![arg_argc, arg_argv])
         };
 
         let result = bld.call(start_fn, &args, None);
-        bld.ret(result);
+
+        // Return rust start function's result from native main()
+        bld.ret(bld.intcast(result, Type::c_int(ccx), true));
     }
 }
 

src/librustc_trans/type_.rs

@@ -140,6 +140,15 @@ impl Type {
         }
     }
 
+    pub fn c_int(ccx: &CrateContext) -> Type {
+        match &ccx.tcx().sess.target.target.target_c_int_width[..] {
+            "16" => Type::i16(ccx),
+            "32" => Type::i32(ccx),
+            "64" => Type::i64(ccx),
+            width => bug!("Unsupported target_c_int_width: {}", width),
+        }
+    }
+
     pub fn int_from_ty(ccx: &CrateContext, t: ast::IntTy) -> Type {
         match t {
             ast::IntTy::Is => ccx.isize_ty(),

src/test/codegen/abi-main-signature-16bit-c-int.rs

@@ -0,0 +1,32 @@
+// Copyright 2017 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.
+
+// Checks the signature of the implicitly generated native main()
+// entry point. It must match C's `int main(int, char **)`.
+
+// This test is for targets with 16bit c_int only.
+// ignore-aarch64
+// ignore-arm
+// ignore-asmjs
+// ignore-hexagon
+// ignore-mips
+// ignore-powerpc
+// ignore-powerpc64
+// ignore-s390x
+// ignore-sparc
+// ignore-wasm32
+// ignore-x86
+// ignore-x86_64
+// ignore-xcore
+
+fn main() {
+}
+
+// CHECK: define i16 @main(i16, i8**)

src/test/codegen/abi-main-signature-32bit-c-int.rs

@@ -0,0 +1,20 @@
+// Copyright 2017 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.
+
+// Checks the signature of the implicitly generated native main()
+// entry point. It must match C's `int main(int, char **)`.
+
+// This test is for targets with 32bit c_int only.
+// ignore-msp430
+
+fn main() {
+}
+
+// CHECK: define i32 @main(i32, i8**)

src/test/run-make/target-specs/my-awesome-platform.json

@@ -4,6 +4,7 @@
     "llvm-target": "i686-unknown-linux-gnu",
     "target-endian": "little",
     "target-pointer-width": "32",
+    "target-c-int-width": "32",
     "arch": "x86",
     "os": "linux",
     "morestack": false

src/test/run-make/target-specs/my-incomplete-platform.json

@@ -3,6 +3,7 @@
     "linker-flavor": "gcc",
     "target-endian": "little",
     "target-pointer-width": "32",
+    "target-c-int-width": "32",
     "arch": "x86",
     "os": "foo",
     "morestack": false

src/test/run-make/target-specs/x86_64-unknown-linux-gnu.json

@@ -5,6 +5,7 @@
     "llvm-target": "x86_64-unknown-linux-gnu",
     "target-endian": "little",
     "target-pointer-width": "64",
+    "target-c-int-width": "32",
     "arch": "x86_64",
     "os": "linux",
     "morestack": false