feat: add no-std common runtime

Add an alloc-backed common library with direct platform I/O.

Build a host attribute macro for async entry points and keep runtime
boilerplate outside application code. Compile the library, macro, and
example directly with rustc through CMake.

Co-Authored-By: luna (openrouter/openai/gpt-5.6-luna): runtime work

CMakeLists.txt

@@ -1,16 +1,17 @@
 cmake_minimum_required(VERSION 3.20)
-project(no_core_write LANGUAGES NONE)
+project(rslibc LANGUAGES NONE)
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 
 find_program(RUSTC rustc REQUIRED)
 
-set(RUST_SOURCE "${CMAKE_CURRENT_SOURCE_DIR}/main.rs")
-set(RUST_BINARY "${CMAKE_CURRENT_BINARY_DIR}/no_core_write${CMAKE_EXECUTABLE_SUFFIX}")
+set(RUST_MACRO_SOURCE "${CMAKE_CURRENT_SOURCE_DIR}/macros/src/lib.rs")
+set(RUST_MACRO "${CMAKE_CURRENT_BINARY_DIR}/rslibc_macros${CMAKE_SHARED_LIBRARY_SUFFIX}")
+set(RUST_LIBRARY_SOURCE "${CMAKE_CURRENT_SOURCE_DIR}/src/lib.rs")
+set(RUST_RUNTIME_SOURCE "${CMAKE_CURRENT_SOURCE_DIR}/runtime/main.rs")
+set(RUST_LIBRARY "${CMAKE_CURRENT_BINARY_DIR}/librslibc.rlib")
+set(RUST_BINARY "${CMAKE_CURRENT_BINARY_DIR}/rslibc_example${CMAKE_EXECUTABLE_SUFFIX}")
 
-# no_core is an unstable rustc feature. RUSTC_BOOTSTRAP lets this deliberately
-# minimal example be built with the installed compiler without Cargo or core.
-set(RUSTC_ENV "RUSTC_BOOTSTRAP=1")
-set(RUSTC_FLAGS -C panic=abort)
+set(RUSTC_FLAGS --edition=2021 -C panic=abort)
 
 # CMAKE_BUILD_TYPE does not automatically affect a custom rustc command.
 # Pass the corresponding optimization/debug-info settings explicitly.
@@ -22,31 +23,63 @@ else()
     list(APPEND RUSTC_FLAGS -C opt-level=0 -C debuginfo=2)
 endif()
 
-# A no_core binary does not get Rust's normal startup/linker setup. Link the
-# small platform system/runtime library needed by the stdout implementation.
+# A no_std binary does not get Rust's normal startup or allocator setup.
+# Use the OS heap and dynamically link only the small platform libraries
+# needed by this runtime.
 if (WIN32)
-    # Use Win32 directly instead of the C runtime; this keeps the executable
-    # small while still writing to the console's stdout handle.
     set(RUSTC_LINK_ARGS
         -l kernel32
+        -l vcruntime
         -C
-        "link-args=/NODEFAULTLIB /ENTRY:mainCRTStartup /SUBSYSTEM:CONSOLE /OPT:REF /OPT:ICF"
+        "link-args=/ENTRY:mainCRTStartup /SUBSYSTEM:CONSOLE /OPT:REF /OPT:ICF"
     )
 elseif (UNIX)
     set(RUSTC_LINK_ARGS -C "link-args=-lc")
 endif()
 
 add_custom_command(
-    OUTPUT "${RUST_BINARY}"
-    COMMAND "${CMAKE_COMMAND}" -E env "${RUSTC_ENV}" "${RUSTC}"
-            "${RUST_SOURCE}"
-            --crate-name no_core_write
-            --crate-type bin
-            -o "${RUST_BINARY}"
-            ${RUSTC_FLAGS}
-            ${RUSTC_LINK_ARGS}
-    DEPENDS "${RUST_SOURCE}"
+    OUTPUT "${RUST_MACRO}"
+    COMMAND "${RUSTC}"
+            "${RUST_MACRO_SOURCE}"
+            --crate-name rslibc_macros
+            --crate-type proc-macro
+            -o "${RUST_MACRO}"
+            --edition=2021
+            -C opt-level=3
+    DEPENDS "${RUST_MACRO_SOURCE}"
     VERBATIM
 )
 
-add_custom_target(no_core_write ALL DEPENDS "${RUST_BINARY}")
+add_custom_command(
+    OUTPUT "${RUST_LIBRARY}"
+    COMMAND "${RUSTC}"
+            "${RUST_LIBRARY_SOURCE}"
+            --crate-name rslibc
+            --crate-type rlib
+            -o "${RUST_LIBRARY}"
+            ${RUSTC_FLAGS}
+    DEPENDS
+            "${RUST_LIBRARY_SOURCE}"
+            "${CMAKE_CURRENT_SOURCE_DIR}/src/io.rs"
+            "${CMAKE_CURRENT_SOURCE_DIR}/src/runtime.rs"
+    VERBATIM
+)
+
+add_custom_command(
+    OUTPUT "${RUST_BINARY}"
+    COMMAND "${RUSTC}"
+            "${RUST_RUNTIME_SOURCE}"
+            --crate-name rslibc_example
+            --crate-type bin
+            --extern "rslibc=${RUST_LIBRARY}"
+            --extern "rslibc_macros=${RUST_MACRO}"
+            -o "${RUST_BINARY}"
+            ${RUSTC_FLAGS}
+            ${RUSTC_LINK_ARGS}
+    DEPENDS "${RUST_RUNTIME_SOURCE}" "${RUST_LIBRARY}" "${RUST_MACRO}"
+    VERBATIM
+)
+
+add_custom_target(rslibc_macros DEPENDS "${RUST_MACRO}")
+add_custom_target(rslibc_library DEPENDS "${RUST_LIBRARY}")
+add_custom_target(rslibc_example ALL DEPENDS "${RUST_BINARY}")