Auto merge of #917 - RalfJung:isolation, r=oli-obk

change flag name: enable-communication -> disable-isolation

r? @oli-obk  -- I think this is a better name for the flag but it is still somewhat clumsy. Suggestions?

README.md

@@ -157,9 +157,9 @@ Several `-Z` flags are relevant for Miri:
   is enforced by default.  This is mostly useful for debugging; it means Miri
   will miss bugs in your program.  However, this can also help to make Miri run
   faster.
-* `-Zmiri-enable-communication` enables communication between the host
-  environment and Miri, i.e., Miri uses the host's random number generator and 
-  all the host environment variables are available during runtime.
+* `-Zmiri-disable-isolation` disables host host isolation.  As a consequence,
+  the program has access to host resources such as environment variables and
+  randomness (and, eventually, file systems and more).
 * `-Zmir-opt-level` controls how many MIR optimizations are performed.  Miri
   overrides the default to be `0`; be advised that using any higher level can
   make Miri miss bugs in your program because they got optimized away.

src/bin/miri.rs

@@ -148,7 +148,7 @@ fn main() {
                 "-Zmiri-disable-validation" => {
                     validate = false;
                 },
-                "-Zmiri-enable-communication" => {
+                "-Zmiri-disable-isolation" => {
                     communicate = true;
                 },
                 "--" => {

tests/run-pass/env-without-isolation.rs

@@ -1,5 +1,5 @@
 // ignore-windows: TODO env var emulation stubbed out on Windows
-// compile-flags: -Zmiri-enable-communication
+// compile-flags: -Zmiri-disable-isolation
 
 fn main() {
     assert_eq!(std::env::var("MIRI_ENV_VAR_TEST"), Ok("0".to_owned()));

tests/run-pass/linux-getrandom-without-isolation.rs

@@ -0,0 +1,18 @@
+// Unfortunately, compiletest_rs does not support 'only-linux',
+// so we need to ignore Windows and macOS instead.
+// ignore-macos: Uses Linux-only APIs
+// ignore-windows: Uses Linux-only APIs
+// compile-flags: -Zmiri-disable-isolation
+#![feature(rustc_private)]
+extern crate libc;
+
+fn main() {
+    let mut buf = [0u8; 5];
+    unsafe {
+        assert_eq!(libc::syscall(libc::SYS_getrandom, 0 as *mut libc::c_void, 0 as libc::size_t, 0 as libc::c_uint), 0);
+        assert_eq!(libc::syscall(libc::SYS_getrandom, buf.as_mut_ptr() as *mut libc::c_void, 5 as libc::size_t, 0 as libc::c_uint), 5);
+
+        assert_eq!(libc::getrandom(0 as *mut libc::c_void, 0 as libc::size_t, 0 as libc::c_uint), 0);
+        assert_eq!(libc::getrandom(buf.as_mut_ptr() as *mut libc::c_void, 5 as libc::size_t, 0 as libc::c_uint), 5);
+    }
+}