Auto merge of #2748 - Aaron1011:wasm32-support, r=RalfJung

Ignore symbol shim clash when symbol is provided by compiler_builtins

When this happens, we ignore the symbol from `compiler_builtins`
in favor of Miri's builtin support.

This allows Miri to target platforms like wasm32-unknown-unknown,
where functions like `memcmp` are provided by `compiler_builtins`.

Author: bors

ci.sh

@@ -108,7 +108,8 @@ case $HOST_TARGET in
     MIRI_TEST_TARGET=i686-pc-windows-msvc run_tests
     MIRI_TEST_TARGET=x86_64-unknown-freebsd run_tests_minimal hello integer vec panic/panic concurrency/simple atomic data_race env/var
     MIRI_TEST_TARGET=aarch64-linux-android run_tests_minimal hello integer vec panic/panic
-    MIRI_TEST_TARGET=wasm32-wasi run_tests_minimal no_std integer
+    MIRI_TEST_TARGET=wasm32-wasi run_tests_minimal no_std integer strings
+    MIRI_TEST_TARGET=wasm32-unknown-unknown run_tests_minimal no_std integer strings
     MIRI_TEST_TARGET=thumbv7em-none-eabihf MIRI_NO_STD=1 run_tests_minimal no_std # no_std embedded architecture
     MIRI_TEST_TARGET=tests/avr.json MIRI_NO_STD=1 run_tests_minimal no_std # JSON target file
     ;;

src/helpers.rs

@@ -943,7 +943,16 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         link_name: Symbol,
     ) -> InterpResult<'tcx, ()> {
         self.check_abi(abi, exp_abi)?;
-        if let Some((body, _)) = self.eval_context_mut().lookup_exported_symbol(link_name)? {
+        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
+            // 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)
+            if self.eval_context_ref().tcx.is_compiler_builtins(instance.def_id().krate) {
+                return Ok(());
+            }
+
             throw_machine_stop!(TerminationInfo::SymbolShimClashing {
                 link_name,
                 span: body.span.data(),

test_dependencies/Cargo.lock

@@ -13,7 +13,7 @@ libc = "0.2"
 num_cpus = "1.10.1"
 
 getrandom_1 = { package = "getrandom", version = "0.1" }
-getrandom = { version = "0.2" }
+getrandom = { version = "0.2", features = ["js"] }
 rand = { version = "0.8", features = ["small_rng"] }
 
 [target.'cfg(not(any(target_arch = "wasm32", target_arch = "wasm64")))'.dependencies]