Merge branch 'main' into flaub/native-machine

risc0/build/src/lib.rs

@@ -318,19 +318,27 @@ pub fn cargo_command(subcmd: &str, rust_flags: &[&str]) -> Command {
     .concat()
     .join("\x1f");
 
-    let cc_path = risc0_data()
-        .unwrap()
-        .join("cpp/bin/riscv32-unknown-elf-gcc");
-    let c_flags = "-march=rv32im -nostdlib";
+    if !cpp_toolchain_override() {
+        let cc_path = risc0_data()
+            .unwrap()
+            .join("cpp/bin/riscv32-unknown-elf-gcc");
+        cmd.env("CC", cc_path)
+            .env("CFLAGS_riscv32im_risc0_zkvm_elf", "-march=rv32im -nostdlib");
+    }
+
     cmd.env("RUSTC", rustc)
         .env("CARGO_ENCODED_RUSTFLAGS", rustflags_envvar)
-        .env("CC", cc_path)
-        .env("CFLAGS_riscv32im_risc0_zkvm_elf", c_flags)
         .args(args);
-
     cmd
 }
 
+fn cpp_toolchain_override() -> bool {
+    // detect if there's an attempt to override the Cpp toolchain.
+    // Overriding the toolchain useful for troubleshooting crates.
+    std::env::var("CC_riscv32im_risc0_zkvm_elf").is_ok()
+        || std::env::var("CFLAGS_riscv32im_risc0_zkvm_elf").is_ok()
+}
+
 /// Builds a static library providing a rust runtime.
 ///
 /// This can be used to build programs for the zkvm which don't depend on