Auto merge of rust-lang#2586 - RalfJung:ffi, r=RalfJung

remove FFI support for macOS

We're only testing this on Linux, and `@thomcc` reports that libffi on macOS is a pain, so let's just disable this for now.

Cargo.toml

@@ -31,8 +31,10 @@ smallvec = "1.7"
 rustc-workspace-hack = "1.0.0"
 measureme = "10.0.0"
 
-[target."cfg(unix)".dependencies]
+[target.'cfg(unix)'.dependencies]
 libc = "0.2"
+
+[target.'cfg(target_os = "linux")'.dependencies]
 libffi = "3.0.0"
 libloading = "0.7"
 

src/machine.rs

@@ -421,8 +421,10 @@ pub struct MiriMachine<'mir, 'tcx> {
     pub(crate) basic_block_count: u64,
 
     /// Handle of the optional shared object file for external functions.
-    #[cfg(unix)]
+    #[cfg(target_os = "linux")]
     pub external_so_lib: Option<(libloading::Library, std::path::PathBuf)>,
+    #[cfg(not(target_os = "linux"))]
+    pub external_so_lib: Option<!>,
 
     /// Run a garbage collector for SbTags every N basic blocks.
     pub(crate) gc_interval: u32,
@@ -485,7 +487,7 @@ impl<'mir, 'tcx> MiriMachine<'mir, 'tcx> {
             report_progress: config.report_progress,
             basic_block_count: 0,
             clock: Clock::new(config.isolated_op == IsolatedOp::Allow),
-            #[cfg(unix)]
+            #[cfg(target_os = "linux")]
             external_so_lib: config.external_so_file.as_ref().map(|lib_file_path| {
                 let target_triple = layout_cx.tcx.sess.opts.target_triple.triple();
                 // Check if host target == the session target.
@@ -507,6 +509,10 @@ impl<'mir, 'tcx> MiriMachine<'mir, 'tcx> {
                     lib_file_path.clone(),
                 )
             }),
+            #[cfg(not(target_os = "linux"))]
+            external_so_lib: config.external_so_file.as_ref().map(|_| {
+                panic!("loading external .so files is only supported on Linux")
+            }),
             gc_interval: config.gc_interval,
             since_gc: 0,
             num_cpus: config.num_cpus,
@@ -648,7 +654,6 @@ impl VisitTags for MiriMachine<'_, '_> {
             preemption_rate: _,
             report_progress: _,
             basic_block_count: _,
-            #[cfg(unix)]
             external_so_lib: _,
             gc_interval: _,
             since_gc: _,

src/shims/ffi_support.rs

@@ -183,9 +183,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         // from: https://docs.rs/libloading/0.7.3/src/libloading/os/unix/mod.rs.html#411
         // using the `libc` crate where this interface is public.
         // No `libc::dladdr` on windows.
-        #[cfg(unix)]
         let mut info = std::mem::MaybeUninit::<libc::Dl_info>::uninit();
-        #[cfg(unix)]
         unsafe {
             if libc::dladdr(*func.deref() as *const _, info.as_mut_ptr()) != 0 {
                 if std::ffi::CStr::from_ptr(info.assume_init().dli_fname).to_str().unwrap()

src/shims/foreign_items.rs

@@ -23,8 +23,6 @@ use rustc_target::{
 
 use super::backtrace::EvalContextExt as _;
 use crate::helpers::{convert::Truncate, target_os_is_unix};
-#[cfg(unix)]
-use crate::shims::ffi_support::EvalContextExt as _;
 use crate::*;
 
 /// Returned by `emulate_foreign_item_by_name`.
@@ -372,8 +370,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         let this = self.eval_context_mut();
 
         // First deal with any external C functions in linked .so file.
-        #[cfg(unix)]
+        #[cfg(target_os = "linux")]
         if this.machine.external_so_lib.as_ref().is_some() {
+            use crate::shims::ffi_support::EvalContextExt as _;
             // An Ok(false) here means that the function being called was not exported
             // by the specified `.so` file; we should continue and check if it corresponds to
             // a provided shim.

src/shims/mod.rs

@@ -1,7 +1,7 @@
 #![warn(clippy::integer_arithmetic)]
 
 mod backtrace;
-#[cfg(unix)]
+#[cfg(target_os = "linux")]
 pub mod ffi_support;
 pub mod foreign_items;
 pub mod intrinsics;