Auto merge of #137457 - JayAndJef:issue-132802-fix, r=<try>

fix for issue 132802: x86 code in `wasm32-unknown-unknown` binaries

This is a direct fix for issue [132802](#132802).
Followed the outline as follows:
> * give a hard error in bootstrap when using gcc to compile for wasm
> * change our CI to use clang instead of gcc
> * add a test that compiling a sample program for wasm32-unknown doesn't give any linker warnings

The `test-various` ci job was also changed.

try-job: test-various
try-job: dist-various-2

Author: bors

src/bootstrap/src/core/sanity.rs

@@ -310,6 +310,17 @@ than building it.
             .entry(*target)
             .or_insert_with(|| Target::from_triple(&target.triple));
 
+        // compiler-rt c fallbacks for wasm cannot be built with gcc
+        if target.contains("wasm") // bare metal targets without wasi sdk
+            && (build.config.optimized_compiler_builtins(*target)
+                || build.config.rust_std_features.contains("compiler-builtins-c"))
+        {
+            let is_clang = is_clang_compiler(build.cc(*target), build);
+            if !is_clang {
+                panic!("only clang supports building c code for wasm targets");
+            }
+        }
+
         if (target.contains("-none-") || target.contains("nvptx"))
             && build.no_std(*target) == Some(false)
         {
@@ -372,3 +383,16 @@ $ pacman -R cmake && pacman -S mingw-w64-x86_64-cmake
         cmd_finder.must_have(s);
     }
 }
+
+/// checks if the compiler at `path` is clang by looking at defined macros
+fn is_clang_compiler(path: PathBuf, build: &Build) -> bool {
+    let cc_output = command(&path)
+        .arg("-E") // preprocess only
+        .arg("-dM") // dump defines
+        .arg("-x")
+        .arg("c")
+        .arg("/dev/null")
+        .run_capture_stdout(build)
+        .stdout();
+    cc_output.contains("#define __clang__ 1")
+}

src/ci/docker/host-x86_64/dist-various-2/Dockerfile

@@ -65,6 +65,10 @@ ENV \
     CXX_i686_unknown_uefi=clang++-11 \
     CC_x86_64_unknown_uefi=clang-11 \
     CXX_x86_64_unknown_uefi=clang++-11 \
+    CC_wasm32_unknown_unknown=clang-11 \
+    CXX_wasm32_unknown_unknown=clang++-11 \
+    CC_wasm32v1_none=clang-11 \
+    CXX_wasm32v1_none=clang++-11 \
     CC=gcc-9 \
     CXX=g++-9
 

src/ci/docker/host-x86_64/test-various/Dockerfile

@@ -4,6 +4,7 @@ ARG DEBIAN_FRONTEND=noninteractive
 RUN apt-get update && apt-get install -y --no-install-recommends \
   clang-11 \
   llvm-11 \
+  gcc-multilib \
   g++ \
   make \
   ninja-build \
@@ -59,8 +60,8 @@ RUN curl -L https://github.com/bytecodealliance/wasmtime/releases/download/v19.0
   tar -xJ
 ENV PATH "$PATH:/wasmtime-v19.0.0-x86_64-linux"
 
-ENV WASM_TARGETS=wasm32-wasip1
-ENV WASM_SCRIPT python3 /checkout/x.py --stage 2 test --host='' --target $WASM_TARGETS \
+ENV WASM_WASIP_TARGET=wasm32-wasip1 
+ENV WASM_WASIP_SCRIPT python3 /checkout/x.py --stage 2 test --host='' --target $WASM_WASIP_TARGET \
   tests/run-make \
   tests/ui \
   tests/mir-opt \
@@ -69,6 +70,12 @@ ENV WASM_SCRIPT python3 /checkout/x.py --stage 2 test --host='' --target $WASM_T
   tests/assembly \
   library/core
 
+ENV WASM_BARE_TARGET=wasm32-unknown-unknown \
+  CC_wasm32_unknown_unknown=clang-11 \
+  CXX_wasm32_unknown_unknown=clang++-11
+ENV WASM_BARE_SCRIPT python3 /checkout/x.py --stage 2 test --host='' --target $WASM_BARE_TARGET \
+  tests/ui/wasm/wasm-builtins-no-linker-warning.rs
+
 ENV NVPTX_TARGETS=nvptx64-nvidia-cuda
 ENV NVPTX_SCRIPT python3 /checkout/x.py --stage 2 test --host='' --target $NVPTX_TARGETS \
   tests/run-make \
@@ -90,4 +97,4 @@ ENV UEFI_TARGETS=aarch64-unknown-uefi,i686-unknown-uefi,x86_64-unknown-uefi \
 ENV UEFI_SCRIPT python3 /checkout/x.py --stage 2 build --host='' --target $UEFI_TARGETS && \
   python3 -u /uefi_qemu_test/run.py
 
-ENV SCRIPT $WASM_SCRIPT && $NVPTX_SCRIPT && $MUSL_SCRIPT && $UEFI_SCRIPT
+ENV SCRIPT $WASM_BARE_SCRIPT && $WASM_WASIP_SCRIPT && $NVPTX_SCRIPT && $MUSL_SCRIPT && $UEFI_SCRIPT

tests/run-make/wasm-builtins-no-linker-warning/foo.rs

@@ -0,0 +1,3 @@
+fn main() {
+    ()
+}

tests/run-make/wasm-builtins-no-linker-warning/rmake.rs

@@ -0,0 +1,7 @@
+//@ only-wasm32-bare
+
+use run_make_support::rustc;
+
+fn main() {
+    rustc().input("foo.rs").target("wasm32-unknown-unknown").arg("-D").arg("linker-messages").run();
+}

tests/ui/wasm/wasm-builtins-no-linker-warning.rs

@@ -0,0 +1,10 @@
+//@ only-wasm32-bare
+//@ compile-flags: -Dlinker-messages
+//@ build-pass
+/// This test checks that linker messages due to gcc lacking
+/// support for wasm32 messages are not emitted when the target
+/// is wasm32-unknown-unknown or wasm32v1-none
+
+fn main() {
+    ()
+}