added better support for structs for extern functions, added a flag to disable list folding and made extern functions automaticly have priority 1

extra_tests/c_extern_structs.c

@@ -0,0 +1,42 @@
+#include <stdint.h>
+#include <time.h>
+
+typedef struct {
+    int64_t a;
+    int64_t b;
+} Pair;
+
+typedef struct {
+    int64_t a;
+    int64_t b;
+    int64_t c;
+} Big;
+
+long long pair_sum(Pair p) {
+    return (long long)(p.a + p.b);
+}
+
+Pair make_pair(long long seed) {
+    Pair out;
+    out.a = seed;
+    out.b = seed + 10;
+    return out;
+}
+
+Big make_big(long long seed) {
+    Big out;
+    out.a = seed;
+    out.b = seed + 1;
+    out.c = seed + 2;
+    return out;
+}
+
+long long big_sum(Big b) {
+    return b.a + b.b + b.c;
+}
+
+long long pair_after_six(long long a, long long b, long long c,
+                         long long d, long long e, long long f,
+                         Pair p) {
+    return a + b + c + d + e + f + p.a + p.b;
+}

extra_tests/c_extern_structs.expected

@@ -0,0 +1,14 @@
+42
+100
+101
+102
+303
+7
+17
+63
+6
+2
+1
+1
+1
+1

extra_tests/c_extern_structs.meta.json

@@ -0,0 +1,4 @@
+{
+  "description": "C extern struct ABI coverage: by-value arg, by-value return, sret return, pointer out",
+  "libs": ["libc.so.6"]
+}

extra_tests/c_extern_structs.sl

@@ -0,0 +1,71 @@
+import stdlib.sl
+
+cstruct Pair
+    cfield a i64
+    cfield b i64
+end
+
+cstruct Big
+    cfield a i64
+    cfield b i64
+    cfield c i64
+end
+
+cstruct LDiv
+    cfield quot i64
+    cfield rem i64
+end
+
+cstruct TimeSpec
+    cfield tv_sec i64
+    cfield tv_nsec i64
+end
+
+extern long long pair_sum(struct Pair p)
+extern struct Pair make_pair(long long seed)
+extern struct Big make_big(long long seed)
+extern long long big_sum(struct Big b)
+extern long long pair_after_six(long long a, long long b, long long c, long long d, long long e, long long f, struct Pair p)
+extern struct LDiv ldiv(long numer, long denom)
+extern int timespec_get(struct TimeSpec* ts, int base)
+extern void exit(int status)
+
+word main
+    Pair.size alloc dup >r
+    r@ 11 Pair.a!
+    r@ 31 Pair.b!
+    r@ pair_sum puti cr
+    r> Pair.size free
+
+    100 make_big dup >r
+    r@ Big.a@ puti cr
+    r@ Big.b@ puti cr
+    r@ Big.c@ puti cr
+    r@ big_sum puti cr
+    r> Big.size free
+
+    7 make_pair dup >r
+    r@ Pair.a@ puti cr
+    r@ Pair.b@ puti cr
+    r> Pair.size free
+
+    Pair.size alloc dup >r
+    r@ 11 Pair.a!
+    r@ 31 Pair.b!
+    1 2 3 4 5 6 r@ pair_after_six puti cr
+    r> Pair.size free
+
+    20 3 ldiv dup >r
+    r@ LDiv.quot@ puti cr
+    r@ LDiv.rem@ puti cr
+    r> LDiv.size free
+
+    TimeSpec.size alloc dup >r
+    r@ 1 timespec_get 1 == if 1 else 0 end puti cr
+    r@ TimeSpec.tv_sec@ 0 > if 1 else 0 end puti cr
+    r@ TimeSpec.tv_nsec@ 0 >= if 1 else 0 end puti cr
+    r@ TimeSpec.tv_nsec@ 1000000000 < if 1 else 0 end puti cr
+    r> TimeSpec.size free
+
+    0 exit
+end

main.py

@@ -292,6 +292,7 @@ class Module:
     variables: Dict[str, str] = field(default_factory=dict)
     prelude: Optional[List[str]] = None
     bss: Optional[List[str]] = None
+    cstruct_layouts: Dict[str, CStructLayout] = field(default_factory=dict)
 
 
 @dataclass(slots=True)
@@ -308,6 +309,23 @@ class StructField:
     size: int
 
 
+@dataclass(slots=True)
+class CStructField:
+    name: str
+    type_name: str
+    offset: int
+    size: int
+    align: int
+
+
+@dataclass(slots=True)
+class CStructLayout:
+    name: str
+    size: int
+    align: int
+    fields: List[CStructField]
+
+
 class MacroContext:
     """Small facade exposed to Python-defined macros."""
 
@@ -460,6 +478,8 @@ Context = Union[Module, Definition]
 
 
 class Parser:
+    EXTERN_DEFAULT_PRIORITY = 1
+
     def __init__(self, dictionary: Dictionary, reader: Optional[Reader] = None) -> None:
         self.dictionary = dictionary
         self.reader = reader or Reader()
@@ -482,6 +502,7 @@ class Parser:
         self.compile_time_vm = CompileTimeVM(self)
         self.custom_prelude: Optional[List[str]] = None
         self.custom_bss: Optional[List[str]] = None
+        self.cstruct_layouts: Dict[str, CStructLayout] = {}
         self._pending_inline_definition: bool = False
         self._pending_priority: Optional[int] = None
 
@@ -588,7 +609,14 @@ class Parser:
         self.pos = 0
         self.variable_labels = {}
         self.variable_words = {}
-        self.context_stack = [Module(forms=[], variables=self.variable_labels)]
+        self.cstruct_layouts = {}
+        self.context_stack = [
+            Module(
+                forms=[],
+                variables=self.variable_labels,
+                cstruct_layouts=self.cstruct_layouts,
+            )
+        ]
         self.definition_stack.clear()
         self.last_defined = None
         self.control_stack = []
@@ -693,6 +721,7 @@ class Parser:
         module.variables = dict(self.variable_labels)
         module.prelude = self.custom_prelude
         module.bss = self.custom_bss
+        module.cstruct_layouts = dict(self.cstruct_layouts)
         return module
 
     def _handle_list_begin(self) -> None:
@@ -717,9 +746,9 @@ class Parser:
             )
         self._pending_priority = value
 
-    def _consume_pending_priority(self) -> int:
+    def _consume_pending_priority(self, *, default: int = 0) -> int:
         if self._pending_priority is None:
-            return 0
+            return default
         value = self._pending_priority
         self._pending_priority = None
         return value
@@ -734,7 +763,7 @@ class Parser:
         if self._eof():
             raise ParseError(f"extern missing name at {token.line}:{token.column}")
 
-        priority = self._consume_pending_priority()
+        priority = self._consume_pending_priority(default=self.EXTERN_DEFAULT_PRIORITY)
         first_token = self._consume()
         if self._try_parse_c_extern(first_token, priority=priority):
             return
@@ -1503,6 +1532,7 @@ class CompileTimeVM:
         self._dl_handles: List[Any] = []  # ctypes.CDLL handles
         self._dl_func_cache: Dict[str, Any] = {}  # name → ctypes callable
         self._ct_libs: List[str] = []  # library names from -l flags
+        self._ctypes_struct_cache: Dict[str, Any] = {}
         self.current_location: Optional[SourceLocation] = None
 
     def reset(self) -> None:
@@ -1734,11 +1764,21 @@ class CompileTimeVM:
 
     _CTYPE_MAP: Dict[str, Any] = {
         "int": ctypes.c_int,
+        "int8_t": ctypes.c_int8,
+        "uint8_t": ctypes.c_uint8,
+        "int16_t": ctypes.c_int16,
+        "uint16_t": ctypes.c_uint16,
+        "int32_t": ctypes.c_int32,
+        "uint32_t": ctypes.c_uint32,
         "long": ctypes.c_long,
         "long long": ctypes.c_longlong,
+        "int64_t": ctypes.c_int64,
         "unsigned int": ctypes.c_uint,
         "unsigned long": ctypes.c_ulong,
+        "unsigned long long": ctypes.c_ulonglong,
+        "uint64_t": ctypes.c_uint64,
         "size_t": ctypes.c_size_t,
+        "ssize_t": ctypes.c_ssize_t,
         "char": ctypes.c_char,
         "char*": ctypes.c_void_p,  # use void* so raw integer addrs work
         "void*": ctypes.c_void_p,
@@ -1746,14 +1786,30 @@ class CompileTimeVM:
         "float": ctypes.c_float,
     }
 
+    def _resolve_struct_ctype(self, struct_name: str) -> Any:
+        cached = self._ctypes_struct_cache.get(struct_name)
+        if cached is not None:
+            return cached
+        layout = self.parser.cstruct_layouts.get(struct_name)
+        if layout is None:
+            raise ParseError(f"unknown cstruct '{struct_name}' used in extern signature")
+        fields = []
+        for field in layout.fields:
+            fields.append((field.name, self._resolve_ctype(field.type_name)))
+        struct_cls = type(f"CTStruct_{sanitize_label(struct_name)}", (ctypes.Structure,), {"_fields_": fields})
+        self._ctypes_struct_cache[struct_name] = struct_cls
+        return struct_cls
+
     def _resolve_ctype(self, type_name: str) -> Any:
         """Map a C type name string to a ctypes type."""
-        t = type_name.strip().replace("*", "* ").replace("  ", " ").strip()
-        if t in self._CTYPE_MAP:
-            return self._CTYPE_MAP[t]
-        # Pointer types
+        t = _canonical_c_type_name(type_name)
         if t.endswith("*"):
             return ctypes.c_void_p
+        if t.startswith("struct "):
+            return self._resolve_struct_ctype(t[len("struct "):].strip())
+        t = t.replace("*", "* ").replace("  ", " ").strip()
+        if t in self._CTYPE_MAP:
+            return self._CTYPE_MAP[t]
         # Default to c_long (64-bit on Linux x86-64)
         return ctypes.c_long
 
@@ -1822,21 +1878,34 @@ class CompileTimeVM:
         # Convert arguments to proper ctypes values
         call_args = []
         for i, raw in enumerate(raw_args):
-            if i < len(arg_types) and arg_types[i] in ("float", "double"):
+            arg_type = _canonical_c_type_name(arg_types[i]) if i < len(arg_types) else None
+            if arg_type in ("float", "double"):
                 # Reinterpret the int64 bits as a double (matching the language's convention)
                 raw_int = _to_i64(int(raw))
                 double_val = struct.unpack("d", struct.pack("q", raw_int))[0]
                 call_args.append(double_val)
+            elif arg_type is not None and arg_type.startswith("struct ") and not arg_type.endswith("*"):
+                struct_name = arg_type[len("struct "):].strip()
+                struct_ctype = self._resolve_struct_ctype(struct_name)
+                call_args.append(struct_ctype.from_address(int(raw)))
             else:
                 call_args.append(int(raw))
 
         result = func(*call_args)
 
         if outputs > 0 and result is not None:
-            ret_type = func._ct_signature[1] if func._ct_signature else None
+            ret_type = _canonical_c_type_name(func._ct_signature[1]) if func._ct_signature else None
             if ret_type in ("float", "double"):
                 int_bits = struct.unpack("q", struct.pack("d", float(result)))[0]
                 self.push(int_bits)
+            elif ret_type is not None and ret_type.startswith("struct "):
+                struct_name = ret_type[len("struct "):].strip()
+                layout = self.parser.cstruct_layouts.get(struct_name)
+                if layout is None:
+                    raise ParseError(f"unknown cstruct '{struct_name}' used in extern return type")
+                out_ptr = self.memory.allocate(layout.size)
+                ctypes.memmove(out_ptr, ctypes.byref(result), layout.size)
+                self.push(out_ptr)
             else:
                 self.push(int(result))
 
@@ -2963,6 +3032,157 @@ _C_TYPE_IGNORED_QUALIFIERS = {
     "_Atomic",
 }
 
+_C_FIELD_TYPE_ALIASES: Dict[str, str] = {
+    "i8": "int8_t",
+    "u8": "uint8_t",
+    "i16": "int16_t",
+    "u16": "uint16_t",
+    "i32": "int32_t",
+    "u32": "uint32_t",
+    "i64": "int64_t",
+    "u64": "uint64_t",
+    "isize": "long",
+    "usize": "size_t",
+    "f32": "float",
+    "f64": "double",
+    "ptr": "void*",
+}
+
+_C_SCALAR_TYPE_INFO: Dict[str, Tuple[int, int, str]] = {
+    "char": (1, 1, "INTEGER"),
+    "signed char": (1, 1, "INTEGER"),
+    "unsigned char": (1, 1, "INTEGER"),
+    "short": (2, 2, "INTEGER"),
+    "short int": (2, 2, "INTEGER"),
+    "unsigned short": (2, 2, "INTEGER"),
+    "unsigned short int": (2, 2, "INTEGER"),
+    "int": (4, 4, "INTEGER"),
+    "unsigned int": (4, 4, "INTEGER"),
+    "int32_t": (4, 4, "INTEGER"),
+    "uint32_t": (4, 4, "INTEGER"),
+    "long": (8, 8, "INTEGER"),
+    "unsigned long": (8, 8, "INTEGER"),
+    "long long": (8, 8, "INTEGER"),
+    "unsigned long long": (8, 8, "INTEGER"),
+    "int64_t": (8, 8, "INTEGER"),
+    "uint64_t": (8, 8, "INTEGER"),
+    "size_t": (8, 8, "INTEGER"),
+    "ssize_t": (8, 8, "INTEGER"),
+    "void": (0, 1, "INTEGER"),
+    "float": (4, 4, "SSE"),
+    "double": (8, 8, "SSE"),
+}
+
+
+def _round_up(value: int, align: int) -> int:
+    if align <= 1:
+        return value
+    return ((value + align - 1) // align) * align
+
+
+def _canonical_c_type_name(type_name: str) -> str:
+    text = " ".join(type_name.strip().split())
+    if not text:
+        return text
+    text = _C_FIELD_TYPE_ALIASES.get(text, text)
+    text = text.replace(" *", "*")
+    return text
+
+
+def _is_struct_type(type_name: str) -> bool:
+    return _canonical_c_type_name(type_name).startswith("struct ")
+
+
+def _c_type_size_align_class(
+    type_name: str,
+    cstruct_layouts: Dict[str, CStructLayout],
+) -> Tuple[int, int, str, Optional[CStructLayout]]:
+    t = _canonical_c_type_name(type_name)
+    if not t:
+        return 8, 8, "INTEGER", None
+    if t.endswith("*"):
+        return 8, 8, "INTEGER", None
+    if t in _C_SCALAR_TYPE_INFO:
+        size, align, cls = _C_SCALAR_TYPE_INFO[t]
+        return size, align, cls, None
+    if t.startswith("struct "):
+        struct_name = t[len("struct "):].strip()
+        layout = cstruct_layouts.get(struct_name)
+        if layout is None:
+            raise CompileError(
+                f"unknown cstruct '{struct_name}' used in extern signature"
+            )
+        return layout.size, layout.align, "STRUCT", layout
+    # Preserve backward compatibility for unknown scalar-ish names.
+    return 8, 8, "INTEGER", None
+
+
+def _merge_eightbyte_class(current: str, incoming: str) -> str:
+    if current == "NO_CLASS":
+        return incoming
+    if current == incoming:
+        return current
+    if current == "INTEGER" or incoming == "INTEGER":
+        return "INTEGER"
+    return incoming
+
+
+def _classify_struct_eightbytes(
+    layout: CStructLayout,
+    cstruct_layouts: Dict[str, CStructLayout],
+    cache: Optional[Dict[str, Optional[List[str]]]] = None,
+) -> Optional[List[str]]:
+    if cache is None:
+        cache = {}
+    cached = cache.get(layout.name)
+    if cached is not None or layout.name in cache:
+        return cached
+
+    if layout.size <= 0:
+        cache[layout.name] = []
+        return []
+    if layout.size > 16:
+        cache[layout.name] = None
+        return None
+
+    chunk_count = (layout.size + 7) // 8
+    classes: List[str] = ["NO_CLASS"] * chunk_count
+
+    for field in layout.fields:
+        f_size, _, f_class, nested = _c_type_size_align_class(field.type_name, cstruct_layouts)
+        if f_size == 0:
+            continue
+        if nested is not None:
+            nested_classes = _classify_struct_eightbytes(nested, cstruct_layouts, cache)
+            if nested_classes is None:
+                cache[layout.name] = None
+                return None
+            base_chunk = field.offset // 8
+            for idx, cls in enumerate(nested_classes):
+                chunk = base_chunk + idx
+                if chunk >= len(classes):
+                    cache[layout.name] = None
+                    return None
+                classes[chunk] = _merge_eightbyte_class(classes[chunk], cls or "INTEGER")
+            continue
+
+        start_chunk = field.offset // 8
+        end_chunk = (field.offset + f_size - 1) // 8
+        if end_chunk >= len(classes):
+            cache[layout.name] = None
+            return None
+        if f_class == "SSE" and start_chunk != end_chunk:
+            cache[layout.name] = None
+            return None
+        for chunk in range(start_chunk, end_chunk + 1):
+            classes[chunk] = _merge_eightbyte_class(classes[chunk], f_class)
+
+    for idx, cls in enumerate(classes):
+        if cls == "NO_CLASS":
+            classes[idx] = "INTEGER"
+    cache[layout.name] = classes
+    return classes
+
 
 def _split_trailing_identifier(text: str) -> Tuple[str, Optional[str]]:
     if not text:
@@ -3083,6 +3303,7 @@ class Assembler:
         dictionary: Dictionary,
         *,
         enable_constant_folding: bool = True,
+        enable_static_list_folding: bool = True,
         enable_peephole_optimization: bool = True,
         loop_unroll_threshold: int = 8,
     ) -> None:
@@ -3094,8 +3315,10 @@ class Assembler:
         self._inline_counter: int = 0
         self._unroll_counter: int = 0
         self._emit_stack: List[str] = []
+        self._cstruct_layouts: Dict[str, CStructLayout] = {}
         self._export_all_defs: bool = False
         self.enable_constant_folding = enable_constant_folding
+        self.enable_static_list_folding = enable_static_list_folding
         self.enable_peephole_optimization = enable_peephole_optimization
         self.loop_unroll_threshold = loop_unroll_threshold
 
@@ -3545,6 +3768,7 @@ class Assembler:
             self._string_literals = {}
             self._float_literals = {}
             self._data_section = emission.data
+            self._cstruct_layouts = dict(module.cstruct_layouts)
 
             valid_defs = (Definition, AsmDefinition)
             raw_defs = [form for form in module.forms if isinstance(form, valid_defs)]
@@ -3560,9 +3784,10 @@ class Assembler:
                 for defn in definitions:
                     if isinstance(defn, Definition):
                         self._fold_constants_in_definition(defn)
-            for defn in definitions:
-                if isinstance(defn, Definition):
-                    self._fold_static_list_literals_definition(defn)
+            if self.enable_static_list_folding:
+                for defn in definitions:
+                    if isinstance(defn, Definition):
+                        self._fold_static_list_literals_definition(defn)
             stray_forms = [form for form in module.forms if not isinstance(form, valid_defs)]
             if stray_forms:
                 raise CompileError("top-level literals or word references are not supported yet")
@@ -4029,6 +4254,222 @@ class Assembler:
 
         raise CompileError(f"unsupported op {node!r}{ctx()}")
 
+    def _emit_mmap_alloc(self, builder: FunctionEmitter, size: int, target_reg: str = "rax") -> None:
+        alloc_size = max(1, int(size))
+        builder.emit("    xor rdi, rdi")
+        builder.emit(f"    mov rsi, {alloc_size}")
+        builder.emit("    mov rdx, 3")
+        builder.emit("    mov r10, 34")
+        builder.emit("    mov r8, -1")
+        builder.emit("    xor r9, r9")
+        builder.emit("    mov rax, 9")
+        builder.emit("    syscall")
+        if target_reg != "rax":
+            builder.emit(f"    mov {target_reg}, rax")
+
+    def _analyze_extern_c_type(self, type_name: str) -> Dict[str, Any]:
+        size, align, cls, layout = _c_type_size_align_class(type_name, self._cstruct_layouts)
+        info: Dict[str, Any] = {
+            "name": _canonical_c_type_name(type_name),
+            "size": size,
+            "align": align,
+            "class": cls,
+            "kind": "struct" if layout is not None else "scalar",
+            "layout": layout,
+            "pass_mode": "scalar",
+            "eightbytes": [],
+        }
+        if layout is not None:
+            eb = _classify_struct_eightbytes(layout, self._cstruct_layouts)
+            info["eightbytes"] = eb or []
+            info["pass_mode"] = "register" if eb is not None else "memory"
+        return info
+
+    def _emit_copy_bytes_from_ptr(
+        self,
+        builder: FunctionEmitter,
+        *,
+        src_ptr_reg: str,
+        dst_expr: str,
+        size: int,
+    ) -> None:
+        copied = 0
+        while copied + 8 <= size:
+            builder.emit(f"    mov r11, [{src_ptr_reg} + {copied}]")
+            builder.emit(f"    mov qword [{dst_expr} + {copied}], r11")
+            copied += 8
+        while copied < size:
+            builder.emit(f"    mov r11b, byte [{src_ptr_reg} + {copied}]")
+            builder.emit(f"    mov byte [{dst_expr} + {copied}], r11b")
+            copied += 1
+
+    def _emit_extern_wordref(self, name: str, word: Word, builder: FunctionEmitter) -> None:
+        inputs = getattr(word, "extern_inputs", 0)
+        outputs = getattr(word, "extern_outputs", 0)
+        signature = getattr(word, "extern_signature", None)
+
+        if signature is None and inputs <= 0 and outputs <= 0:
+            builder.emit(f"    call {name}")
+            return
+
+        arg_types = list(signature[0]) if signature else ["long"] * inputs
+        ret_type = signature[1] if signature else ("long" if outputs > 0 else "void")
+
+        if len(arg_types) != inputs and signature is not None:
+            suffix = f" while emitting '{self._emit_stack[-1]}'" if self._emit_stack else ""
+            raise CompileError(f"extern '{name}' mismatch: {inputs} inputs vs {len(arg_types)} types{suffix}")
+
+        arg_infos = [self._analyze_extern_c_type(t) for t in arg_types]
+        ret_info = self._analyze_extern_c_type(ret_type)
+
+        regs = ["rdi", "rsi", "rdx", "rcx", "r8", "r9"]
+        xmm_regs = [f"xmm{i}" for i in range(8)]
+
+        ret_uses_sret = ret_info["kind"] == "struct" and ret_info["pass_mode"] == "memory"
+        int_idx = 1 if ret_uses_sret else 0
+        xmm_idx = 0
+
+        arg_locs: List[Dict[str, Any]] = []
+        stack_cursor = 0
+
+        for info in arg_infos:
+            if info["kind"] == "struct":
+                if info["pass_mode"] == "register":
+                    classes: List[str] = list(info["eightbytes"])
+                    need_int = sum(1 for c in classes if c == "INTEGER")
+                    need_xmm = sum(1 for c in classes if c == "SSE")
+                    if int_idx + need_int <= len(regs) and xmm_idx + need_xmm <= len(xmm_regs):
+                        chunks: List[Tuple[str, str, int]] = []
+                        int_off = int_idx
+                        xmm_off = xmm_idx
+                        for chunk_idx, cls in enumerate(classes):
+                            if cls == "SSE":
+                                chunks.append((cls, xmm_regs[xmm_off], chunk_idx * 8))
+                                xmm_off += 1
+                            else:
+                                chunks.append(("INTEGER", regs[int_off], chunk_idx * 8))
+                                int_off += 1
+                        int_idx = int_off
+                        xmm_idx = xmm_off
+                        arg_locs.append({"mode": "struct_reg", "chunks": chunks, "info": info})
+                    else:
+                        stack_size = _round_up(int(info["size"]), 8)
+                        stack_off = stack_cursor
+                        stack_cursor += stack_size
+                        arg_locs.append({"mode": "struct_stack", "stack_off": stack_off, "info": info})
+                else:
+                    stack_size = _round_up(int(info["size"]), 8)
+                    stack_off = stack_cursor
+                    stack_cursor += stack_size
+                    arg_locs.append({"mode": "struct_stack", "stack_off": stack_off, "info": info})
+                continue
+
+            if info["class"] == "SSE":
+                if xmm_idx < len(xmm_regs):
+                    arg_locs.append({"mode": "scalar_reg", "reg": xmm_regs[xmm_idx], "class": "SSE"})
+                    xmm_idx += 1
+                else:
+                    stack_off = stack_cursor
+                    stack_cursor += 8
+                    arg_locs.append({"mode": "scalar_stack", "stack_off": stack_off, "class": "SSE"})
+            else:
+                if int_idx < len(regs):
+                    arg_locs.append({"mode": "scalar_reg", "reg": regs[int_idx], "class": "INTEGER"})
+                    int_idx += 1
+                else:
+                    stack_off = stack_cursor
+                    stack_cursor += 8
+                    arg_locs.append({"mode": "scalar_stack", "stack_off": stack_off, "class": "INTEGER"})
+
+        # Preserve and realign RSP for C ABI calls regardless current call depth.
+        stack_bytes = max(15, int(stack_cursor) + 15)
+        builder.emit("    mov r14, rsp")
+        builder.emit(f"    sub rsp, {stack_bytes}")
+        builder.emit("    and rsp, -16")
+
+        if ret_info["kind"] == "struct":
+            self._emit_mmap_alloc(builder, int(ret_info["size"]), target_reg="r15")
+            if ret_uses_sret:
+                builder.emit("    mov rdi, r15")
+
+        total_args = len(arg_locs)
+        for idx, loc in enumerate(reversed(arg_locs)):
+            addr = f"[r12 + {idx * 8}]" if idx > 0 else "[r12]"
+            mode = str(loc["mode"])
+
+            if mode == "scalar_reg":
+                reg = str(loc["reg"])
+                cls = str(loc["class"])
+                if cls == "SSE":
+                    builder.emit(f"    mov rax, {addr}")
+                    builder.emit(f"    movq {reg}, rax")
+                else:
+                    builder.emit(f"    mov {reg}, {addr}")
+                continue
+
+            if mode == "scalar_stack":
+                stack_off = int(loc["stack_off"])
+                builder.emit(f"    mov rax, {addr}")
+                builder.emit(f"    mov qword [rsp + {stack_off}], rax")
+                continue
+
+            if mode == "struct_reg":
+                chunks: List[Tuple[str, str, int]] = list(loc["chunks"])
+                builder.emit(f"    mov rax, {addr}")
+                for cls, target, off in chunks:
+                    if cls == "SSE":
+                        builder.emit(f"    movq {target}, [rax + {off}]")
+                    else:
+                        builder.emit(f"    mov {target}, [rax + {off}]")
+                continue
+
+            if mode == "struct_stack":
+                stack_off = int(loc["stack_off"])
+                size = int(loc["info"]["size"])
+                builder.emit(f"    mov rax, {addr}")
+                self._emit_copy_bytes_from_ptr(builder, src_ptr_reg="rax", dst_expr=f"rsp + {stack_off}", size=size)
+                continue
+
+            raise CompileError(f"internal extern lowering error for '{name}': unknown arg mode {mode!r}")
+
+        if total_args:
+            builder.emit(f"    add r12, {total_args * 8}")
+
+        builder.emit(f"    mov al, {xmm_idx}")
+        builder.emit(f"    call {name}")
+
+        builder.emit("    mov rsp, r14")
+
+        if ret_info["kind"] == "struct":
+            if not ret_uses_sret:
+                ret_classes: List[str] = list(ret_info["eightbytes"])
+                int_ret_regs = ["rax", "rdx"]
+                xmm_ret_regs = ["xmm0", "xmm1"]
+                int_ret_idx = 0
+                xmm_ret_idx = 0
+                for chunk_idx, cls in enumerate(ret_classes):
+                    off = chunk_idx * 8
+                    if cls == "SSE":
+                        src = xmm_ret_regs[xmm_ret_idx]
+                        xmm_ret_idx += 1
+                        builder.emit(f"    movq [r15 + {off}], {src}")
+                    else:
+                        src = int_ret_regs[int_ret_idx]
+                        int_ret_idx += 1
+                        builder.emit(f"    mov [r15 + {off}], {src}")
+            builder.emit("    sub r12, 8")
+            builder.emit("    mov [r12], r15")
+            return
+
+        if _ctype_uses_sse(ret_type):
+            builder.emit("    sub r12, 8")
+            builder.emit("    movq rax, xmm0")
+            builder.emit("    mov [r12], rax")
+        elif outputs == 1:
+            builder.push_from("rax")
+        elif outputs > 1:
+            raise CompileError("extern only supports 0 or 1 scalar output")
+
     def _emit_wordref(self, name: str, builder: FunctionEmitter) -> None:
         word = self.dictionary.lookup(name)
         if word is None:
@@ -4048,114 +4489,7 @@ class Assembler:
             word.intrinsic(builder)
             return
         if getattr(word, "is_extern", False):
-            inputs = getattr(word, "extern_inputs", 0)
-            outputs = getattr(word, "extern_outputs", 0)
-            signature = getattr(word, "extern_signature", None)
-
-            if signature is not None or inputs > 0 or outputs > 0:
-                regs = ["rdi", "rsi", "rdx", "rcx", "r8", "r9"]
-                xmm_regs = [f"xmm{i}" for i in range(8)]
-
-                arg_types = signature[0] if signature else []
-                ret_type = signature[1] if signature else None
-
-                if len(arg_types) != inputs and signature:
-                    suffix = f" while emitting '{self._emit_stack[-1]}'" if self._emit_stack else ""
-                    raise CompileError(f"extern '{name}' mismatch: {inputs} inputs vs {len(arg_types)} types{suffix}")
-
-                int_idx = 0
-                xmm_idx = 0
-
-                mapping: List[Tuple[str, str]] = []  # (type, target)
-
-                # Assign registers for first args; overflow goes to stack
-                if not arg_types:
-                    # Legacy/Raw mode: assume all ints
-                    for i in range(inputs):
-                        if int_idx < len(regs):
-                            mapping.append(("int", regs[int_idx]))
-                            int_idx += 1
-                        else:
-                            mapping.append(("int", "stack"))
-                else:
-                    for type_name in arg_types:
-                        if type_name in ("float", "double"):
-                            if xmm_idx < len(xmm_regs):
-                                mapping.append(("float", xmm_regs[xmm_idx]))
-                                xmm_idx += 1
-                            else:
-                                mapping.append(("float", "stack"))
-                        else:
-                            if int_idx < len(regs):
-                                mapping.append(("int", regs[int_idx]))
-                                int_idx += 1
-                            else:
-                                mapping.append(("int", "stack"))
-
-                # Count stack slots required
-                stack_slots = sum(1 for t, target in mapping if target == "stack")
-                # stack allocation in bytes; make it a multiple of 16 for alignment
-                stack_bytes = ((stack_slots * 8 + 15) // 16) * 16 if stack_slots > 0 else 0
-
-                # Prepare stack-passed arguments: allocate space (16-byte multiple)
-                if stack_bytes:
-                    builder.emit(f"    sub rsp, {stack_bytes}")
-
-                # Read all arguments from the CT stack by indexed addressing
-                # (without advancing r12) and write them to registers or the
-                # prepared spill area. After all reads are emitted we advance
-                # r12 once by the total number of arguments to pop them.
-                total_args = len(mapping)
-                if stack_slots:
-                    stack_write_idx = stack_slots - 1
-                else:
-                    stack_write_idx = 0
-
-                # Iterate over reversed mapping (right-to-left) but use an
-                # index to address the CT stack without modifying r12.
-                for idx, (typ, target) in enumerate(reversed(mapping)):
-                    addr = f"[r12 + {idx * 8}]" if idx > 0 else "[r12]"
-                    if target == "stack":
-                        # Read spilled arg from indexed CT stack slot and store
-                        # it into the caller's spill area at the computed offset.
-                        builder.emit(f"    mov rax, {addr}")
-                        offset = stack_write_idx * 8
-                        builder.emit(f"    mov [rsp + {offset}], rax")
-                        stack_write_idx -= 1
-                    else:
-                        if typ == "float":
-                            builder.emit(f"    mov rax, {addr}")
-                            builder.emit(f"    movq {target}, rax")
-                        else:
-                            builder.emit(f"    mov {target}, {addr}")
-
-                # Advance the CT stack pointer once to pop all arguments.
-                if total_args:
-                    builder.emit(f"    add r12, {total_args * 8}")
-
-                # Call the external function. We allocated a multiple-of-16
-                # area for spilled args above so `rsp` is already aligned
-                # for the call; set `al` (SSE count) then call directly.
-                builder.emit(f"    mov al, {xmm_idx}")
-                builder.emit(f"    call {name}")
-
-                # Restore stack after the call
-                if stack_bytes:
-                    builder.emit(f"    add rsp, {stack_bytes}")
-
-                # Handle Return Value
-                if _ctype_uses_sse(ret_type):
-                    # Result in xmm0, move to stack
-                    builder.emit("    sub r12, 8")
-                    builder.emit("    movq rax, xmm0")
-                    builder.emit("    mov [r12], rax")
-                elif outputs == 1:
-                    builder.push_from("rax")
-                elif outputs > 1:
-                    raise CompileError("extern only supports 0 or 1 output")
-            else:
-                # Emit call to unresolved symbol (let linker resolve it)
-                builder.emit(f"    call {name}")
+            self._emit_extern_wordref(name, word, builder)
         else:
             builder.emit(f"    call {sanitize_label(name)}")
 
@@ -5346,6 +5680,27 @@ PY_EXEC_GLOBALS: Dict[str, Any] = {
 }
 
 
+def _parse_cfield_type(parser: Parser, struct_name: str) -> str:
+    if parser._eof():
+        raise ParseError(f"field type missing in cstruct '{struct_name}'")
+    tok = parser.next_token().lexeme
+
+    if tok == "struct":
+        if parser._eof():
+            raise ParseError(f"struct field type missing name in cstruct '{struct_name}'")
+        name_tok = parser.next_token().lexeme
+        type_name = f"struct {name_tok}"
+        if not parser._eof():
+            peek = parser.peek_token()
+            if peek is not None and set(peek.lexeme) == {"*"}:
+                type_name += peek.lexeme
+                parser.next_token()
+        return _canonical_c_type_name(type_name)
+
+    canonical = _canonical_c_type_name(tok)
+    return _canonical_c_type_name(_C_FIELD_TYPE_ALIASES.get(canonical, canonical))
+
+
 def macro_struct_begin(ctx: MacroContext) -> Optional[List[Op]]:
     parser = ctx.parser
     if parser._eof():
@@ -5402,6 +5757,84 @@ def macro_struct_begin(ctx: MacroContext) -> Optional[List[Op]]:
     parser.tokens[parser.pos:parser.pos] = generated
     return None
 
+
+def macro_cstruct_begin(ctx: MacroContext) -> Optional[List[Op]]:
+    parser = ctx.parser
+    if parser._eof():
+        raise ParseError("cstruct name missing after 'cstruct'")
+    name_token = parser.next_token()
+    struct_name = name_token.lexeme
+    fields: List[CStructField] = []
+    current_offset = 0
+    max_align = 1
+
+    while True:
+        if parser._eof():
+            raise ParseError("unterminated cstruct definition (missing 'end')")
+        token = parser.next_token()
+        if token.lexeme == "end":
+            break
+        if token.lexeme != "cfield":
+            raise ParseError(
+                f"expected 'cfield' or 'end' in cstruct '{struct_name}' definition"
+            )
+        if parser._eof():
+            raise ParseError("field name missing in cstruct definition")
+        field_name_token = parser.next_token()
+        type_name = _parse_cfield_type(parser, struct_name)
+        field_size, field_align, _, _ = _c_type_size_align_class(type_name, parser.cstruct_layouts)
+        if field_size <= 0:
+            raise ParseError(
+                f"invalid cfield type '{type_name}' for '{field_name_token.lexeme}' in cstruct '{struct_name}'"
+            )
+
+        current_offset = _round_up(current_offset, field_align)
+        fields.append(
+            CStructField(
+                name=field_name_token.lexeme,
+                type_name=type_name,
+                offset=current_offset,
+                size=field_size,
+                align=field_align,
+            )
+        )
+        current_offset += field_size
+        if field_align > max_align:
+            max_align = field_align
+
+    total_size = _round_up(current_offset, max_align)
+    parser.cstruct_layouts[struct_name] = CStructLayout(
+        name=struct_name,
+        size=total_size,
+        align=max_align,
+        fields=fields,
+    )
+
+    generated: List[Token] = []
+    _struct_emit_definition(generated, name_token, f"{struct_name}.size", [str(total_size)])
+    _struct_emit_definition(generated, name_token, f"{struct_name}.align", [str(max_align)])
+    for field in fields:
+        size_word = f"{struct_name}.{field.name}.size"
+        offset_word = f"{struct_name}.{field.name}.offset"
+        _struct_emit_definition(generated, name_token, size_word, [str(field.size)])
+        _struct_emit_definition(generated, name_token, offset_word, [str(field.offset)])
+        if field.size == 8:
+            _struct_emit_definition(
+                generated,
+                name_token,
+                f"{struct_name}.{field.name}@",
+                [offset_word, "+", "@"],
+            )
+            _struct_emit_definition(
+                generated,
+                name_token,
+                f"{struct_name}.{field.name}!",
+                ["swap", offset_word, "+", "swap", "!"],
+            )
+
+    parser.tokens[parser.pos:parser.pos] = generated
+    return None
+
 def macro_here(ctx: MacroContext) -> Optional[List[Op]]:
     tok = ctx.parser._last_token
     if tok is None:
@@ -5422,6 +5855,7 @@ def bootstrap_dictionary() -> Dictionary:
     dictionary.register(Word(name="with", immediate=True, macro=macro_with))
     dictionary.register(Word(name="macro", immediate=True, macro=macro_begin_text_macro))
     dictionary.register(Word(name="struct", immediate=True, macro=macro_struct_begin))
+    dictionary.register(Word(name="cstruct", immediate=True, macro=macro_cstruct_begin))
     _register_compile_time_primitives(dictionary)
     _register_runtime_intrinsics(dictionary)
     return dictionary
@@ -5694,9 +6128,17 @@ class BuildCache:
         key = self._hash_str(str(source.resolve()))
         return self.cache_dir / f"{key}.json"
 
-    def flags_hash(self, debug: bool, folding: bool, peephole: bool, entry_mode: str) -> str:
+    def flags_hash(
+        self,
+        debug: bool,
+        folding: bool,
+        static_list_folding: bool,
+        peephole: bool,
+        entry_mode: str,
+    ) -> str:
         return self._hash_str(
-            f"debug={debug},folding={folding},peephole={peephole},entry_mode={entry_mode}"
+            f"debug={debug},folding={folding},static_list_folding={static_list_folding},"
+            f"peephole={peephole},entry_mode={entry_mode}"
         )
 
     def _file_info(self, path: Path) -> dict:
@@ -5857,6 +6299,38 @@ def build_static_library(obj_path: Path, archive_path: Path) -> None:
     subprocess.run(["ar", "rcs", str(archive_path), str(obj_path)], check=True)
 
 
+def _load_sidecar_meta_libs(source: Path) -> List[str]:
+    """Return additional linker libs from sibling <source>.meta.json."""
+    meta_path = source.with_suffix(".meta.json")
+    if not meta_path.exists():
+        return []
+    try:
+        payload = json.loads(meta_path.read_text())
+    except Exception as exc:
+        print(f"[warn] failed to read {meta_path}: {exc}")
+        return []
+    libs = payload.get("libs")
+    if not isinstance(libs, list):
+        return []
+    out: List[str] = []
+    for item in libs:
+        if isinstance(item, str) and item:
+            out.append(item)
+    return out
+
+
+def _build_ct_sidecar_shared(source: Path, temp_dir: Path) -> Optional[Path]:
+    """Build sibling <source>.c into a shared object for --ct-run-main externs."""
+    c_path = source.with_suffix(".c")
+    if not c_path.exists():
+        return None
+    temp_dir.mkdir(parents=True, exist_ok=True)
+    so_path = temp_dir / f"{source.stem}.ctlib.so"
+    cmd = ["cc", "-shared", "-fPIC", str(c_path), "-o", str(so_path)]
+    subprocess.run(cmd, check=True)
+    return so_path
+
+
 def run_repl(
     compiler: Compiler,
     temp_dir: Path,
@@ -7150,6 +7624,11 @@ def cli(argv: Sequence[str]) -> int:
     parser.add_argument("--repl", action="store_true", help="interactive REPL; source file is optional")
     parser.add_argument("-l", dest="libs", action="append", default=[], help="pass library to linker (e.g. -l m or -l libc.so.6)")
     parser.add_argument("--no-folding", action="store_true", help="disable constant folding optimization")
+    parser.add_argument(
+        "--no-static-list-folding",
+        action="store_true",
+        help="disable static list-literal folding (lists stay runtime-allocated)",
+    )
     parser.add_argument("--no-peephole", action="store_true", help="disable peephole optimizations")
     parser.add_argument("--no-cache", action="store_true", help="disable incremental build cache")
     parser.add_argument("--ct-run-main", action="store_true", help="execute 'main' via the compile-time VM after parsing")
@@ -7203,6 +7682,7 @@ def cli(argv: Sequence[str]) -> int:
 
     artifact_kind = args.artifact
     folding_enabled = not args.no_folding
+    static_list_folding_enabled = not args.no_static_list_folding
     peephole_enabled = not args.no_peephole
 
     if args.ct_run_main and artifact_kind != "exe":
@@ -7253,8 +7733,28 @@ def cli(argv: Sequence[str]) -> int:
     if not args.repl and artifact_kind in {"static", "obj"} and args.libs:
         print("[warn] --libs ignored for static/object outputs")
 
+    ct_run_libs: List[str] = list(args.libs)
+    if args.source is not None:
+        for lib in _load_sidecar_meta_libs(args.source):
+            if lib not in args.libs:
+                args.libs.append(lib)
+            if lib not in ct_run_libs:
+                ct_run_libs.append(lib)
+
+    if args.ct_run_main and args.source is not None:
+        try:
+            ct_sidecar = _build_ct_sidecar_shared(args.source, args.temp_dir)
+        except subprocess.CalledProcessError as exc:
+            print(f"[error] failed to build compile-time sidecar library: {exc}")
+            return 1
+        if ct_sidecar is not None:
+            so_lib = str(ct_sidecar.resolve())
+            if so_lib not in ct_run_libs:
+                ct_run_libs.append(so_lib)
+
     compiler = Compiler(include_paths=[Path("."), Path("./stdlib"), *args.include_paths])
     compiler.assembler.enable_constant_folding = folding_enabled
+    compiler.assembler.enable_static_list_folding = static_list_folding_enabled
     compiler.assembler.enable_peephole_optimization = peephole_enabled
 
     cache: Optional[BuildCache] = None
@@ -7271,7 +7771,13 @@ def cli(argv: Sequence[str]) -> int:
         asm_text: Optional[str] = None
         fhash = ""
         if cache and not args.ct_run_main:
-            fhash = cache.flags_hash(args.debug, folding_enabled, peephole_enabled, entry_mode)
+            fhash = cache.flags_hash(
+                args.debug,
+                folding_enabled,
+                static_list_folding_enabled,
+                peephole_enabled,
+                entry_mode,
+            )
             manifest = cache.load_manifest(args.source)
             if manifest and cache.check_fresh(manifest, fhash):
                 cached = cache.get_cached_asm(manifest)
@@ -7287,13 +7793,19 @@ def cli(argv: Sequence[str]) -> int:
 
             if cache and not args.ct_run_main:
                 if not fhash:
-                    fhash = cache.flags_hash(args.debug, folding_enabled, peephole_enabled, entry_mode)
+                    fhash = cache.flags_hash(
+                        args.debug,
+                        folding_enabled,
+                        static_list_folding_enabled,
+                        peephole_enabled,
+                        entry_mode,
+                    )
                 has_ct = bool(compiler.parser.compile_time_vm._ct_executed)
                 cache.save(args.source, compiler._loaded_files, fhash, asm_text, has_ct_effects=has_ct)
 
         if args.ct_run_main:
             try:
-                compiler.run_compile_time_word("main", libs=args.libs)
+                compiler.run_compile_time_word("main", libs=ct_run_libs)
             except CompileTimeError as exc:
                 print(f"[error] compile-time execution of 'main' failed: {exc}")
                 return 1

test.py

@@ -25,6 +25,7 @@ DEFAULT_EXTRA_TESTS = [
     "extra_tests/ct_test.sl",
     "extra_tests/args.sl",
     "extra_tests/c_extern.sl",
+    "extra_tests/c_extern_structs.sl",
     "extra_tests/fn_test.sl",
     "extra_tests/nob_test.sl",
 ]
@@ -364,7 +365,11 @@ class TestRunner:
             reason = case.config.skip_reason or "skipped via metadata"
             return CaseResult(case, "skipped", "skip", reason)
         start = time.perf_counter()
-        compile_proc = self._compile(case)
+        try:
+            fixture_libs = self._prepare_case_native_libs(case)
+        except RuntimeError as exc:
+            return CaseResult(case, "failed", "fixture", str(exc))
+        compile_proc = self._compile(case, extra_libs=fixture_libs)
         if case.config.expect_compile_error:
             result = self._handle_expected_compile_failure(case, compile_proc)
             result.duration = time.perf_counter() - start
@@ -424,10 +429,19 @@ class TestRunner:
             return CaseResult(case, "updated", "compare", "; ".join(updated_notes), details=None, duration=duration)
         return CaseResult(case, "passed", "run", "ok", details=None, duration=duration)
 
-    def _compile(self, case: TestCase) -> subprocess.CompletedProcess[str]:
-        cmd = [sys.executable, str(self.main_py), str(case.source), "-o", str(case.binary_path)]
+    def _compile(self, case: TestCase, *, extra_libs: Optional[Sequence[str]] = None) -> subprocess.CompletedProcess[str]:
+        cmd = [
+            sys.executable,
+            str(self.main_py),
+            str(case.source),
+            "-o",
+            str(case.binary_path),
+            "--no-cache",
+        ]
         for lib in case.config.libs:
             cmd.extend(["-l", lib])
+        for lib in (extra_libs or []):
+            cmd.extend(["-l", lib])
         if self.args.ct_run_main:
             cmd.append("--ct-run-main")
         if self.args.verbose:
@@ -446,6 +460,56 @@ class TestRunner:
             env=self._env_for(case),
         )
 
+    def _prepare_case_native_libs(self, case: TestCase) -> List[str]:
+        """Build optional per-test native C fixtures and return linkable artifacts."""
+        c_source = case.source.with_suffix(".c")
+        if not c_source.exists():
+            return []
+
+        cc = shutil.which("cc") or shutil.which("gcc") or shutil.which("clang")
+        if cc is None:
+            raise RuntimeError("no C compiler found (expected one of: cc, gcc, clang)")
+
+        ar = shutil.which("ar")
+        if ar is None:
+            raise RuntimeError("'ar' is required to build static C fixtures")
+
+        obj_path = case.build_dir / f"{case.binary_stub}_fixture.o"
+        archive_path = case.build_dir / f"lib{case.binary_stub}_fixture.a"
+
+        compile_cmd = [cc, "-O2", "-c", str(c_source), "-o", str(obj_path)]
+        archive_cmd = [ar, "rcs", str(archive_path), str(obj_path)]
+
+        if self.args.verbose:
+            print(f"{format_status('CMD', 'blue')} {quote_cmd(compile_cmd)}")
+            print(f"{format_status('CMD', 'blue')} {quote_cmd(archive_cmd)}")
+
+        compile_proc = subprocess.run(
+            compile_cmd,
+            cwd=self.root,
+            capture_output=True,
+            text=True,
+            env=self._env_for(case),
+        )
+        if compile_proc.returncode != 0:
+            raise RuntimeError(
+                "failed to compile C fixture:\n" + self._format_process_output(compile_proc)
+            )
+
+        archive_proc = subprocess.run(
+            archive_cmd,
+            cwd=self.root,
+            capture_output=True,
+            text=True,
+            env=self._env_for(case),
+        )
+        if archive_proc.returncode != 0:
+            raise RuntimeError(
+                "failed to archive C fixture:\n" + self._format_process_output(archive_proc)
+            )
+
+        return [str(archive_path.resolve())]
+
     def _run_binary(self, case: TestCase) -> subprocess.CompletedProcess[str]:
         runtime_cmd = [self._runtime_entry(case), *case.runtime_args()]
         runtime_cmd = wrap_runtime_command(runtime_cmd)