Auto merge of rust-lang#3108 - RalfJung:dlsym, r=RalfJung

refactor dlsym: dispatch symbols via the normal shim mechanism

This avoids having to adjust Miri when switching between invoking the function via a linked symbol vs via dlsym.

src/tools/miri/src/helpers.rs

@@ -960,7 +960,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         self.check_abi(abi, exp_abi)?;
         if let Some((body, instance)) = self.eval_context_mut().lookup_exported_symbol(link_name)? {
             // If compiler-builtins is providing the symbol, then don't treat it as a clash.
-            // We'll use our built-in implementation in `emulate_foreign_item_by_name` for increased
+            // We'll use our built-in implementation in `emulate_foreign_item_inner` for increased
             // performance. Note that this means we won't catch any undefined behavior in
             // compiler-builtins when running other crates, but Miri can still be run on
             // compiler-builtins itself (or any crate that uses it as a normal dependency)

src/tools/miri/src/lib.rs

@@ -8,6 +8,7 @@
 #![feature(yeet_expr)]
 #![feature(nonzero_ops)]
 #![feature(round_ties_even)]
+#![feature(let_chains)]
 #![feature(lint_reasons)]
 #![feature(trait_upcasting)]
 // Configure clippy and other lints
@@ -86,9 +87,8 @@ pub use rustc_const_eval::interpret::*;
 // Resolve ambiguity.
 pub use rustc_const_eval::interpret::{self, AllocMap, PlaceTy, Provenance as _};
 
-pub use crate::shims::dlsym::{Dlsym, EvalContextExt as _};
 pub use crate::shims::env::{EnvVars, EvalContextExt as _};
-pub use crate::shims::foreign_items::EvalContextExt as _;
+pub use crate::shims::foreign_items::{DynSym, EvalContextExt as _};
 pub use crate::shims::intrinsics::EvalContextExt as _;
 pub use crate::shims::os_str::EvalContextExt as _;
 pub use crate::shims::panic::{CatchUnwindData, EvalContextExt as _};

src/tools/miri/src/machine.rs

@@ -707,11 +707,10 @@ impl<'mir, 'tcx> MiriMachine<'mir, 'tcx> {
                 );
             }
             "android" => {
-                // "signal"
+                // "signal" -- just needs a non-zero pointer value (function does not even get called),
+                // but we arrange for this to be callable anyway (it will then do nothing).
                 let layout = this.machine.layouts.const_raw_ptr;
-                let dlsym = Dlsym::from_str("signal".as_bytes(), &this.tcx.sess.target.os)?
-                    .expect("`signal` must be an actual dlsym on android");
-                let ptr = this.fn_ptr(FnVal::Other(dlsym));
+                let ptr = this.fn_ptr(FnVal::Other(DynSym::from_str("signal")));
                 let val = ImmTy::from_scalar(Scalar::from_pointer(ptr, this), layout);
                 Self::alloc_extern_static(this, "signal", val)?;
                 // A couple zero-initialized pointer-sized extern statics.
@@ -867,7 +866,7 @@ impl<'mir, 'tcx> MiriInterpCxExt<'mir, 'tcx> for MiriInterpCx<'mir, 'tcx> {
 /// Machine hook implementations.
 impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
     type MemoryKind = MiriMemoryKind;
-    type ExtraFnVal = Dlsym;
+    type ExtraFnVal = DynSym;
 
     type FrameExtra = FrameExtra<'tcx>;
     type AllocExtra = AllocExtra<'tcx>;
@@ -939,15 +938,15 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
     #[inline(always)]
     fn call_extra_fn(
         ecx: &mut MiriInterpCx<'mir, 'tcx>,
-        fn_val: Dlsym,
+        fn_val: DynSym,
         abi: Abi,
         args: &[FnArg<'tcx, Provenance>],
         dest: &PlaceTy<'tcx, Provenance>,
         ret: Option<mir::BasicBlock>,
-        _unwind: mir::UnwindAction,
+        unwind: mir::UnwindAction,
     ) -> InterpResult<'tcx> {
         let args = ecx.copy_fn_args(args)?; // FIXME: Should `InPlace` arguments be reset to uninit?
-        ecx.call_dlsym(fn_val, abi, &args, dest, ret)
+        ecx.emulate_dyn_sym(fn_val, abi, &args, dest, ret, unwind)
     }
 
     #[inline(always)]