Added:

- `build.kind = "efi"` — UEFI PE32+ executable support. Links with `-shared -nostdlib -Wl,-dll -Wl,--subsystem,10`, output via `efi_path()` with `.efi` extension, rejected by `dcr run`.
- `build.kind = "elf"` — bare-metal ELF executable support. Uses `elf_path()` output path, rejected by `dcr run`, no extra linker flags.

Fixed:

- `dcr run` with `--target` or `build.target` now correctly finds the binary in the arch-specific target directory.
- `dcr run` checks profile-specific `build.{profile}.kind` before rejecting library builds (previously only checked `build.kind`).
- `dcr clean` now reads `build.target` from `dcr.toml` when no `--target` flag is given.
- Linux: target directory is now consistent — `target/<arch>-unknown-linux-gnu/<profile>/` (no stale `target/<profile>/`).
- `dcr.lock` is now populated with all resolved dependencies (registry, path, git) instead of being always empty.
- Git dependencies are now properly recognized and recorded in `dcr.lock`.
- `is_registry_dep` correctly identifies version-based registry dependency tables (`{ version = "..." }`) and rejects tables with unknown keys.
- `dcr test` accepts `--debug`/`--release` flags (defaults to `debug` profile instead of always `release`).
- Build fingerprint cache (`build_cache_path`) now includes `target_dir` — different targets no longer share a single cache entry.
- `object_path` no longer hardcodes the `src/` prefix — works correctly with custom `build.roots` (e.g. `roots = ["lib"]`).
- `dcr update` now generates `.exe` candidates for all Windows targets, not just `x86_64-pc-windows-msvc`.
- Compiler existence is verified before starting the build (clear error if compiler is not found in PATH).
- Consolidated duplicate `OUTPUT_MUTEX` definitions — MSVC backend now uses the shared mutex from `common.rs`.
- Registry cache root directory is created if missing (prevents cryptic errors when `~/.dcr/` does not exist).

src/core/builder/common.rs

@@ -5,6 +5,10 @@ use std::sync::{Mutex, OnceLock};
 
 static OUTPUT_MUTEX: OnceLock<Mutex<()>> = OnceLock::new();
 
+pub fn get_output_lock() -> &'static Mutex<()> {
+    OUTPUT_MUTEX.get_or_init(|| Mutex::new(()))
+}
+
 pub fn collect_sources(
     roots: &[PathBuf],
     extensions: &[&str],
@@ -230,10 +234,16 @@ pub fn normalize_source_path(path: &Path) -> String {
 
 pub fn object_path(obj_dir: &Path, source: &str, obj_ext: &str) -> String {
     let src_path = Path::new(source);
-    let rel = src_path
-        .strip_prefix("./src")
-        .or_else(|_| src_path.strip_prefix("src"))
-        .unwrap_or(src_path);
+    let stripped = src_path.strip_prefix("./").unwrap_or(src_path);
+    let rel = stripped
+        .components()
+        .skip(1)
+        .collect::<std::path::PathBuf>();
+    let rel = if rel.components().next().is_some() {
+        rel
+    } else {
+        stripped.to_path_buf()
+    };
     let mut out = obj_dir.join(rel);
     out.set_extension(obj_ext.trim_start_matches('.'));
     out.to_string_lossy().to_string()

src/core/builder/gas.rs

@@ -18,7 +18,10 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
     };
     let start_time = Instant::now();
     let sources = collect_sources(ctx)?;
-    let obj_dir = Path::new("./target").join(ctx.profile).join("obj");
+    let obj_dir = match ctx.target_dir {
+        Some(dir) => Path::new(dir).join("obj"),
+        None => Path::new("./target").join(ctx.profile).join("obj"),
+    };
     let objects = build_objects(assembler, &sources, &obj_dir, ctx, "o")?;
 
     if ctx.kind == "staticlib" {
@@ -80,6 +83,8 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
 
     let out_path = if ctx.kind == "sharedlib" {
         platform::shared_lib_path(ctx.profile, &final_name, ctx.target_dir)
+    } else if ctx.kind == "elf" {
+        platform::elf_path(ctx.profile, &final_name, ctx.target_dir)
     } else {
         platform::bin_path(ctx.profile, &final_name, ctx.target_dir)
     };

src/core/builder/mod.rs

@@ -33,6 +33,12 @@ pub struct BuildContext<'a> {
 
 pub fn build(ctx: &BuildContext) -> Result<f64, String> {
     let compiler = ctx.compiler.to_lowercase();
+    if !check_compiler_exists(ctx.compiler) {
+        return Err(format!(
+            "Compiler not found: {}. Make sure it is installed and available in PATH.",
+            ctx.compiler
+        ));
+    }
     if compiler.contains("clang-cl") {
         return msvc::build(ctx);
     }
@@ -48,6 +54,14 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
     unix_cc::build(ctx)
 }
 
+fn check_compiler_exists(compiler: &str) -> bool {
+    let name = if compiler.is_empty() { "cc" } else { compiler };
+    std::process::Command::new(name)
+        .arg("--version")
+        .output()
+        .is_ok()
+}
+
 pub fn collect_sources(ctx: &BuildContext) -> Result<Vec<String>, String> {
     let compiler = ctx.compiler.to_lowercase();
     if compiler.contains("clang-cl") || compiler == "cl" || compiler.contains("msvc") {

src/core/builder/msvc.rs

@@ -18,7 +18,10 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
     }
     let start_time = Instant::now();
     let sources = collect_sources(ctx)?;
-    let obj_dir = Path::new("./target").join(ctx.profile).join("obj");
+    let obj_dir = match ctx.target_dir {
+        Some(dir) => Path::new(dir).join("obj"),
+        None => Path::new("./target").join(ctx.profile).join("obj"),
+    };
     let objects = build_objects(compiler, &sources, &obj_dir, ctx, "obj")?;
 
     if ctx.kind == "staticlib" {
@@ -92,6 +95,8 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
     }
     let out_path = if ctx.kind == "sharedlib" {
         platform::shared_lib_path(ctx.profile, ctx.project_name, ctx.target_dir)
+    } else if ctx.kind == "elf" {
+        platform::elf_path(ctx.profile, ctx.project_name, ctx.target_dir)
     } else {
         platform::bin_path(ctx.profile, ctx.project_name, ctx.target_dir)
     };
@@ -185,8 +190,6 @@ fn default_flags(profile: &str) -> &'static [&'static str] {
     }
 }
 
-static OUTPUT_MUTEX: std::sync::Mutex<()> = std::sync::Mutex::new(());
-
 fn build_objects(
     compiler: &str,
     sources: &[String],
@@ -282,7 +285,7 @@ fn build_object(
         }
     }
 
-    let _lock = OUTPUT_MUTEX.lock().unwrap();
+    let _lock = common::get_output_lock().lock().unwrap();
 
     if !output.status.success() {
         eprint!("{}", clean_stdout);

src/core/builder/nasm.rs

@@ -18,7 +18,10 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
     };
     let start_time = Instant::now();
     let sources = collect_sources(ctx)?;
-    let obj_dir = Path::new("./target").join(ctx.profile).join("obj");
+    let obj_dir = match ctx.target_dir {
+        Some(dir) => Path::new(dir).join("obj"),
+        None => Path::new("./target").join(ctx.profile).join("obj"),
+    };
     let objects = build_objects(assembler, &sources, &obj_dir, ctx, "o")?;
 
     if ctx.kind == "staticlib" {
@@ -80,6 +83,8 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
 
     let out_path = if ctx.kind == "sharedlib" {
         platform::shared_lib_path(ctx.profile, &final_name, ctx.target_dir)
+    } else if ctx.kind == "elf" {
+        platform::elf_path(ctx.profile, &final_name, ctx.target_dir)
     } else {
         platform::bin_path(ctx.profile, &final_name, ctx.target_dir)
     };

src/core/builder/unix_cc.rs

@@ -20,7 +20,10 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
         ctx.exclude_dirs,
         ctx.include_paths,
     )?;
-    let obj_dir = Path::new("./target").join(ctx.profile).join("obj");
+    let obj_dir = match ctx.target_dir {
+        Some(dir) => Path::new(dir).join("obj"),
+        None => Path::new("./target").join(ctx.profile).join("obj"),
+    };
     let objects = build_objects(compiler, &sources, &obj_dir, ctx, "o")?;
 
     if ctx.kind == "staticlib" {
@@ -51,6 +54,12 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
             cmd.arg("-shared");
         }
     }
+    if ctx.kind == "efi" {
+        cmd.arg("-shared");
+        cmd.arg("-nostdlib");
+        cmd.arg("-Wl,-dll");
+        cmd.arg("-Wl,--subsystem,10");
+    }
     for obj in &objects {
         cmd.arg(obj);
     }
@@ -73,6 +82,10 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
 
     let out_path = if ctx.kind == "sharedlib" {
         platform::shared_lib_path(ctx.profile, &final_name, ctx.target_dir)
+    } else if ctx.kind == "efi" {
+        platform::efi_path(ctx.profile, &final_name, ctx.target_dir)
+    } else if ctx.kind == "elf" {
+        platform::elf_path(ctx.profile, &final_name, ctx.target_dir)
     } else {
         platform::bin_path(ctx.profile, &final_name, ctx.target_dir)
     };