rdrand: Add 32-bit x86 support

Also add tests for 32-bit x86

.travis.yml

@@ -1,9 +1,11 @@
 language: rust
 os: linux
 
-# Targets that we just build (rather than run and test)
 env:
   global:
+    # All of the supported x86 Linux targets
+    - LINUX_TARGETS="x86_64-unknown-linux-gnu x86_64-unknown-linux-musl i686-unknown-linux-gnu i686-unknown-linux-musl"
+    # Targets that we just build (rather than run and test)
     - STD_TARGETS="x86_64-sun-solaris x86_64-unknown-cloudabi x86_64-unknown-freebsd x86_64-fuchsia x86_64-unknown-netbsd x86_64-unknown-redox x86_64-fortanix-unknown-sgx"
     - NO_STD_TARGETS="x86_64-unknown-uefi x86_64-unknown-hermit x86_64-unknown-l4re-uclibc x86_64-uwp-windows-gnu x86_64-wrs-vxworks"
 
@@ -112,6 +114,18 @@ jobs:
       name: "OSX, nightly, docs"
       os: osx
 
+    - name: "cross-platform tests"
+      rust: nightly
+      addons:
+        apt:
+          packages:
+          - gcc-multilib
+      install:
+        - echo $LINUX_TARGETS | xargs -n1 rustup target add
+      script:
+        # We run tests for all supported x86 Linux targets
+        - echo $LINUX_TARGETS | xargs -t -n1 cargo test --target
+
     - name: "cross-platform build only"
       rust: nightly
       install:

src/lib.rs

@@ -185,7 +185,8 @@ cfg_if! {
         #[path = "rdrand.rs"] mod imp;
     } else if #[cfg(feature = "custom")] {
         use custom as imp;
-    } else if #[cfg(all(feature = "cpu", target_arch = "x86_64"))] {
+    } else if #[cfg(all(feature = "cpu",
+                        any(target_arch = "x86_64", target_arch = "x86")))] {
         #[path = "rdrand.rs"] mod imp;
     } else {
         compile_error!("\

src/rdrand.rs

@@ -7,23 +7,30 @@
 // except according to those terms.
 
 //! Implementation for SGX using RDRAND instruction
-#[cfg(not(target_feature = "rdrand"))]
-use crate::util::LazyBool;
 use crate::Error;
-use core::arch::x86_64::_rdrand64_step;
 use core::mem;
 
+cfg_if! {
+    if #[cfg(target_arch = "x86_64")] {
+        use core::arch::x86_64 as arch;
+        use arch::_rdrand64_step as rdrand_step;
+    } else if #[cfg(target_arch = "x86")] {
+        use core::arch::x86 as arch;
+        use arch::_rdrand32_step as rdrand_step;
+    }
+}
+
 // Recommendation from "Intel® Digital Random Number Generator (DRNG) Software
 // Implementation Guide" - Section 5.2.1 and "Intel® 64 and IA-32 Architectures
 // Software Developer’s Manual" - Volume 1 - Section 7.3.17.1.
 const RETRY_LIMIT: usize = 10;
-const WORD_SIZE: usize = mem::size_of::<u64>();
+const WORD_SIZE: usize = mem::size_of::<usize>();
 
 #[target_feature(enable = "rdrand")]
 unsafe fn rdrand() -> Result<[u8; WORD_SIZE], Error> {
     for _ in 0..RETRY_LIMIT {
         let mut el = mem::zeroed();
-        if _rdrand64_step(&mut el) == 1 {
+        if rdrand_step(&mut el) == 1 {
             // AMD CPUs from families 14h to 16h (pre Ryzen) sometimes fail to
             // set CF on bogus random data, so we check these values explicitly.
             // See https://github.com/systemd/systemd/issues/11810#issuecomment-489727505
@@ -53,11 +60,13 @@ fn is_rdrand_supported() -> bool {
 // https://github.com/rust-lang-nursery/stdsimd/issues/464
 #[cfg(not(target_feature = "rdrand"))]
 fn is_rdrand_supported() -> bool {
-    use core::arch::x86_64::__cpuid;
-    // SAFETY: All x86_64 CPUs support CPUID leaf 1
+    use crate::util::LazyBool;
+
+    // SAFETY: All Rust x86 targets are new enough to have CPUID, and if CPUID
+    // is supported, CPUID leaf 1 is always supported.
     const FLAG: u32 = 1 << 30;
     static HAS_RDRAND: LazyBool = LazyBool::new();
-    HAS_RDRAND.unsync_init(|| unsafe { (__cpuid(1).ecx & FLAG) != 0 })
+    HAS_RDRAND.unsync_init(|| unsafe { (arch::__cpuid(1).ecx & FLAG) != 0 })
 }
 
 pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {

src/test_cpu.rs

@@ -1,5 +1,5 @@
 // We only test the CPU-based RNG source on supported architectures.
-#![cfg(target_arch = "x86_64")]
+#![cfg(any(target_arch = "x86_64", target_arch = "x86"))]
 
 #[path = "rdrand.rs"]
 mod rdrand;