diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8f871ce7e6..ecfc80fdc8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -204,6 +204,7 @@ install(TARGETS zig DESTINATION bin)
 
 install(FILES ${C_HEADERS} DESTINATION ${C_HEADERS_DEST})
 
+install(FILES "${CMAKE_SOURCE_DIR}/std/build.zig" DESTINATION "${ZIG_STD_DEST}")
 install(FILES "${CMAKE_SOURCE_DIR}/std/c/darwin.zig" DESTINATION "${ZIG_STD_DEST}/c")
 install(FILES "${CMAKE_SOURCE_DIR}/std/c/index.zig" DESTINATION "${ZIG_STD_DEST}/c")
 install(FILES "${CMAKE_SOURCE_DIR}/std/c/linux.zig" DESTINATION "${ZIG_STD_DEST}/c")
@@ -234,6 +235,7 @@ install(FILES "${CMAKE_SOURCE_DIR}/std/rand.zig" DESTINATION "${ZIG_STD_DEST}")
 install(FILES "${CMAKE_SOURCE_DIR}/std/rand_test.zig" DESTINATION "${ZIG_STD_DEST}")
 install(FILES "${CMAKE_SOURCE_DIR}/std/sort.zig" DESTINATION "${ZIG_STD_DEST}")
 install(FILES "${CMAKE_SOURCE_DIR}/std/special/bootstrap.zig" DESTINATION "${ZIG_STD_DEST}/special")
+install(FILES "${CMAKE_SOURCE_DIR}/std/special/build_runner.zig" DESTINATION "${ZIG_STD_DEST}/special")
 install(FILES "${CMAKE_SOURCE_DIR}/std/special/builtin.zig" DESTINATION "${ZIG_STD_DEST}/special")
 install(FILES "${CMAKE_SOURCE_DIR}/std/special/compiler_rt.zig" DESTINATION "${ZIG_STD_DEST}/special")
 install(FILES "${CMAKE_SOURCE_DIR}/std/special/test_runner.zig" DESTINATION "${ZIG_STD_DEST}/special")
diff --git a/README.md b/README.md
index 594abcaa5e..68f9e62627 100644
--- a/README.md
+++ b/README.md
@@ -82,13 +82,12 @@ the Zig compiler itself:
  * gcc >= 5.0.0 or clang >= 3.6.0
  * cmake >= 2.8.5
 
-#### Runtime Dependencies
+#### Library Dependencies
 
 These libraries must be installed on your system, with the development files
 available. The Zig compiler dynamically links against them.
 
- * LLVM == 4.x
- * libclang == 4.x
+ * LLVM, Clang, and LLD libraries == 4.x
 
 ### Debug / Development Build
 
diff --git a/doc/langref.md b/doc/langref.md
index 7b6ba4b294..529191bf26 100644
--- a/doc/langref.md
+++ b/doc/langref.md
@@ -633,3 +633,10 @@ Invokes the panic handler function. By default the panic handler function
 calls the public `panic` function exposed in the root source file, or
 if there is not one specified, invokes the one provided in
 `std/special/panic.zig`.
+
+### @bitcast(comptime DestType: type, value: var) -> DestType
+
+Transmutes memory from one type to another without changing any bits.
+The source and destination types must have the same size. This function
+can be used to, for example, reinterpret a pointer, or convert a `f32` to a
+`u32`.
diff --git a/src/all_types.hpp b/src/all_types.hpp
index 07c409c0f0..347654351c 100644
--- a/src/all_types.hpp
+++ b/src/all_types.hpp
@@ -1196,6 +1196,7 @@ enum BuiltinFnId {
     BuiltinFnIdSetGlobalSection,
     BuiltinFnIdSetGlobalLinkage,
     BuiltinFnIdPanic,
+    BuiltinFnIdBitCast,
 };
 
 struct BuiltinFnEntry {
@@ -1719,7 +1720,7 @@ enum IrInstructionId {
     IrInstructionIdFnProto,
     IrInstructionIdTestComptime,
     IrInstructionIdInitEnum,
-    IrInstructionIdPointerReinterpret,
+    IrInstructionIdBitCast,
     IrInstructionIdWidenOrShorten,
     IrInstructionIdIntToPtr,
     IrInstructionIdPtrToInt,
@@ -2369,10 +2370,11 @@ struct IrInstructionInitEnum {
     LLVMValueRef tmp_ptr;
 };
 
-struct IrInstructionPointerReinterpret {
+struct IrInstructionBitCast {
     IrInstruction base;
 
-    IrInstruction *ptr;
+    IrInstruction *dest_type;
+    IrInstruction *target;
 };
 
 struct IrInstructionWidenOrShorten {
diff --git a/src/analyze.cpp b/src/analyze.cpp
index fc7915da5a..6a669cf425 100644
--- a/src/analyze.cpp
+++ b/src/analyze.cpp
@@ -3355,7 +3355,6 @@ bool type_has_bits(TypeTableEntry *type_entry) {
 bool type_requires_comptime(TypeTableEntry *type_entry) {
     switch (get_underlying_type(type_entry)->id) {
         case TypeTableEntryIdInvalid:
-        case TypeTableEntryIdUnreachable:
         case TypeTableEntryIdVar:
         case TypeTableEntryIdTypeDecl:
             zig_unreachable();
@@ -3383,6 +3382,7 @@ bool type_requires_comptime(TypeTableEntry *type_entry) {
         case TypeTableEntryIdPointer:
         case TypeTableEntryIdEnumTag:
         case TypeTableEntryIdVoid:
+        case TypeTableEntryIdUnreachable:
             return false;
     }
     zig_unreachable();
diff --git a/src/codegen.cpp b/src/codegen.cpp
index d7e4dc17ec..25290bc279 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -47,7 +47,7 @@ static void init_darwin_native(CodeGen *g) {
     }
 }
 
-static PackageTableEntry *new_package(const char *root_src_dir, const char *root_src_path) {
+PackageTableEntry *new_package(const char *root_src_dir, const char *root_src_path) {
     PackageTableEntry *entry = allocate<PackageTableEntry>(1);
     entry->package_table.init(4);
     buf_init_from_str(&entry->root_src_dir, root_src_dir);
@@ -1345,12 +1345,12 @@ static LLVMValueRef ir_render_cast(CodeGen *g, IrExecutable *executable,
     zig_unreachable();
 }
 
-static LLVMValueRef ir_render_pointer_reinterpret(CodeGen *g, IrExecutable *executable,
-        IrInstructionPointerReinterpret *instruction)
+static LLVMValueRef ir_render_bitcast(CodeGen *g, IrExecutable *executable,
+        IrInstructionBitCast *instruction)
 {
     TypeTableEntry *wanted_type = instruction->base.value.type;
-    LLVMValueRef ptr = ir_llvm_value(g, instruction->ptr);
-    return LLVMBuildBitCast(g->builder, ptr, wanted_type->type_ref, "");
+    LLVMValueRef target = ir_llvm_value(g, instruction->target);
+    return LLVMBuildBitCast(g->builder, target, wanted_type->type_ref, "");
 }
 
 static LLVMValueRef ir_render_widen_or_shorten(CodeGen *g, IrExecutable *executable,
@@ -2776,8 +2776,8 @@ static LLVMValueRef ir_render_instruction(CodeGen *g, IrExecutable *executable,
             return ir_render_init_enum(g, executable, (IrInstructionInitEnum *)instruction);
         case IrInstructionIdStructInit:
             return ir_render_struct_init(g, executable, (IrInstructionStructInit *)instruction);
-        case IrInstructionIdPointerReinterpret:
-            return ir_render_pointer_reinterpret(g, executable, (IrInstructionPointerReinterpret *)instruction);
+        case IrInstructionIdBitCast:
+            return ir_render_bitcast(g, executable, (IrInstructionBitCast *)instruction);
         case IrInstructionIdWidenOrShorten:
             return ir_render_widen_or_shorten(g, executable, (IrInstructionWidenOrShorten *)instruction);
         case IrInstructionIdPtrToInt:
@@ -3638,8 +3638,14 @@ static void do_code_gen(CodeGen *g) {
             } else {
                 assert(var->gen_arg_index != SIZE_MAX);
                 TypeTableEntry *gen_type;
+                FnGenParamInfo *gen_info = &fn_table_entry->type_entry->data.fn.gen_param_info[var->src_arg_index];
+
                 if (handle_is_ptr(var->value->type)) {
-                    gen_type = fn_table_entry->type_entry->data.fn.gen_param_info[var->src_arg_index].type;
+                    if (gen_info->is_byval) {
+                        gen_type = var->value->type;
+                    } else {
+                        gen_type = gen_info->type;
+                    }
                     var->value_ref = LLVMGetParam(fn, var->gen_arg_index);
                 } else {
                     gen_type = var->value->type;
@@ -4254,6 +4260,7 @@ static void define_builtin_fns(CodeGen *g) {
     create_builtin_fn(g, BuiltinFnIdSetGlobalSection, "setGlobalSection", 2);
     create_builtin_fn(g, BuiltinFnIdSetGlobalLinkage, "setGlobalLinkage", 2);
     create_builtin_fn(g, BuiltinFnIdPanic, "panic", 1);
+    create_builtin_fn(g, BuiltinFnIdBitCast, "bitcast", 2);
 }
 
 static void add_compile_var(CodeGen *g, const char *name, ConstExprValue *value) {
diff --git a/src/codegen.hpp b/src/codegen.hpp
index 5b39e3d36c..6b493e4464 100644
--- a/src/codegen.hpp
+++ b/src/codegen.hpp
@@ -45,6 +45,7 @@ void codegen_set_mios_version_min(CodeGen *g, Buf *mios_version_min);
 void codegen_set_linker_script(CodeGen *g, const char *linker_script);
 void codegen_set_omit_zigrt(CodeGen *g, bool omit_zigrt);
 
+PackageTableEntry *new_package(const char *root_src_dir, const char *root_src_path);
 void codegen_add_root_code(CodeGen *g, Buf *source_dir, Buf *source_basename, Buf *source_code);
 
 void codegen_parseh(CodeGen *g, Buf *src_dirname, Buf *src_basename, Buf *source_code);
diff --git a/src/ir.cpp b/src/ir.cpp
index 9e1ef9339e..0a0756f27a 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -480,8 +480,8 @@ static constexpr IrInstructionId ir_instruction_id(IrInstructionInitEnum *) {
     return IrInstructionIdInitEnum;
 }
 
-static constexpr IrInstructionId ir_instruction_id(IrInstructionPointerReinterpret *) {
-    return IrInstructionIdPointerReinterpret;
+static constexpr IrInstructionId ir_instruction_id(IrInstructionBitCast *) {
+    return IrInstructionIdBitCast;
 }
 
 static constexpr IrInstructionId ir_instruction_id(IrInstructionWidenOrShorten *) {
@@ -1940,14 +1940,16 @@ static IrInstruction *ir_build_init_enum_from(IrBuilder *irb, IrInstruction *old
     return new_instruction;
 }
 
-static IrInstruction *ir_build_pointer_reinterpret(IrBuilder *irb, Scope *scope, AstNode *source_node,
-        IrInstruction *ptr)
+static IrInstruction *ir_build_bit_cast(IrBuilder *irb, Scope *scope, AstNode *source_node,
+        IrInstruction *dest_type, IrInstruction *target)
 {
-    IrInstructionPointerReinterpret *instruction = ir_build_instruction<IrInstructionPointerReinterpret>(
+    IrInstructionBitCast *instruction = ir_build_instruction<IrInstructionBitCast>(
             irb, scope, source_node);
-    instruction->ptr = ptr;
+    instruction->dest_type = dest_type;
+    instruction->target = target;
 
-    ir_ref_instruction(ptr, irb->current_basic_block);
+    if (dest_type) ir_ref_instruction(dest_type, irb->current_basic_block);
+    ir_ref_instruction(target, irb->current_basic_block);
 
     return &instruction->base;
 }
@@ -2664,11 +2666,12 @@ static IrInstruction *ir_instruction_initenum_get_dep(IrInstructionInitEnum *ins
     }
 }
 
-static IrInstruction *ir_instruction_pointerreinterpret_get_dep(IrInstructionPointerReinterpret *instruction,
+static IrInstruction *ir_instruction_bitcast_get_dep(IrInstructionBitCast *instruction,
         size_t index)
 {
     switch (index) {
-        case 0: return instruction->ptr;
+        case 0: return instruction->dest_type;
+        case 1: return instruction->target;
         default: return nullptr;
     }
 }
@@ -2925,8 +2928,8 @@ static IrInstruction *ir_instruction_get_dep(IrInstruction *instruction, size_t
             return ir_instruction_testcomptime_get_dep((IrInstructionTestComptime *) instruction, index);
         case IrInstructionIdInitEnum:
             return ir_instruction_initenum_get_dep((IrInstructionInitEnum *) instruction, index);
-        case IrInstructionIdPointerReinterpret:
-            return ir_instruction_pointerreinterpret_get_dep((IrInstructionPointerReinterpret *) instruction, index);
+        case IrInstructionIdBitCast:
+            return ir_instruction_bitcast_get_dep((IrInstructionBitCast *) instruction, index);
         case IrInstructionIdWidenOrShorten:
             return ir_instruction_widenorshorten_get_dep((IrInstructionWidenOrShorten *) instruction, index);
         case IrInstructionIdIntToPtr:
@@ -4197,6 +4200,20 @@ static IrInstruction *ir_gen_builtin_fn_call(IrBuilder *irb, Scope *scope, AstNo
 
                 return ir_build_panic(irb, scope, node, arg0_value);
             }
+        case BuiltinFnIdBitCast:
+            {
+                AstNode *arg0_node = node->data.fn_call_expr.params.at(0);
+                IrInstruction *arg0_value = ir_gen_node(irb, arg0_node, scope);
+                if (arg0_value == irb->codegen->invalid_instruction)
+                    return arg0_value;
+
+                AstNode *arg1_node = node->data.fn_call_expr.params.at(1);
+                IrInstruction *arg1_value = ir_gen_node(irb, arg1_node, scope);
+                if (arg1_value == irb->codegen->invalid_instruction)
+                    return arg1_value;
+
+                return ir_build_bit_cast(irb, scope, node, arg0_value, arg1_value);
+            }
     }
     zig_unreachable();
 }
@@ -6364,34 +6381,6 @@ static IrInstruction *ir_analyze_maybe_wrap(IrAnalyze *ira, IrInstruction *sourc
     return result;
 }
 
-static IrInstruction *ir_analyze_pointer_reinterpret(IrAnalyze *ira, IrInstruction *source_instr,
-        IrInstruction *ptr, TypeTableEntry *wanted_type)
-{
-    if (ptr->value.type->id != TypeTableEntryIdPointer &&
-        ptr->value.type->id != TypeTableEntryIdMaybe)
-    {
-        ir_add_error(ira, ptr, buf_sprintf("expected pointer, found '%s'", buf_ptr(&ptr->value.type->name)));
-        return ira->codegen->invalid_instruction;
-    }
-
-    if (instr_is_comptime(ptr)) {
-        ConstExprValue *val = ir_resolve_const(ira, ptr, UndefOk);
-        if (!val)
-            return ira->codegen->invalid_instruction;
-
-        IrInstructionConst *const_instruction = ir_create_instruction<IrInstructionConst>(&ira->new_irb,
-                source_instr->scope, source_instr->source_node);
-        const_instruction->base.value = *val;
-        const_instruction->base.value.type = wanted_type;
-        return &const_instruction->base;
-    }
-
-    IrInstruction *result = ir_build_pointer_reinterpret(&ira->new_irb, source_instr->scope,
-            source_instr->source_node, ptr);
-    result->value.type = wanted_type;
-    return result;
-}
-
 static IrInstruction *ir_analyze_err_wrap_payload(IrAnalyze *ira, IrInstruction *source_instr,
         IrInstruction *value, TypeTableEntry *wanted_type)
 {
@@ -6829,24 +6818,6 @@ static IrInstruction *ir_analyze_cast(IrAnalyze *ira, IrInstruction *source_inst
         }
     }
 
-    // explicit cast from pointer to another pointer
-    if ((actual_type->id == TypeTableEntryIdPointer || actual_type->id == TypeTableEntryIdFn) &&
-        (wanted_type->id == TypeTableEntryIdPointer || wanted_type->id == TypeTableEntryIdFn))
-    {
-        return ir_analyze_pointer_reinterpret(ira, source_instr, value, wanted_type);
-    }
-
-    // explicit cast from maybe pointer to another maybe pointer
-    if (actual_type->id == TypeTableEntryIdMaybe &&
-        (actual_type->data.maybe.child_type->id == TypeTableEntryIdPointer ||
-            actual_type->data.maybe.child_type->id == TypeTableEntryIdFn) &&
-        wanted_type->id == TypeTableEntryIdMaybe &&
-        (wanted_type->data.maybe.child_type->id == TypeTableEntryIdPointer ||
-            wanted_type->data.maybe.child_type->id == TypeTableEntryIdFn))
-    {
-        return ir_analyze_pointer_reinterpret(ira, source_instr, value, wanted_type);
-    }
-
     // explicit cast from child type of maybe type to maybe type
     if (wanted_type->id == TypeTableEntryIdMaybe) {
         if (types_match_const_cast_only(wanted_type->data.maybe.child_type, actual_type)) {
@@ -8986,6 +8957,7 @@ static TypeTableEntry *ir_analyze_instruction_elem_ptr(IrAnalyze *ira, IrInstruc
 
         ConstExprValue *array_ptr_val;
         if (array_ptr->value.special != ConstValSpecialRuntime &&
+            array_ptr->value.data.x_ptr.mut != ConstPtrMutRuntimeVar &&
             (array_ptr_val = const_ptr_pointee(&array_ptr->value)) &&
             array_ptr_val->special != ConstValSpecialRuntime &&
             (array_type->id != TypeTableEntryIdPointer ||
@@ -12210,6 +12182,50 @@ static TypeTableEntry *ir_analyze_instruction_panic(IrAnalyze *ira, IrInstructio
     return ir_finish_anal(ira, ira->codegen->builtin_types.entry_unreachable);
 }
 
+static TypeTableEntry *ir_analyze_instruction_bit_cast(IrAnalyze *ira, IrInstructionBitCast *instruction) {
+    IrInstruction *dest_type_value = instruction->dest_type->other;
+    TypeTableEntry *dest_type = ir_resolve_type(ira, dest_type_value);
+    if (type_is_invalid(dest_type))
+        return ira->codegen->builtin_types.entry_invalid;
+
+    IrInstruction *target = instruction->target->other;
+    TypeTableEntry *src_type = target->value.type;
+    if (type_is_invalid(src_type))
+        return ira->codegen->builtin_types.entry_invalid;
+
+    ensure_complete_type(ira->codegen, dest_type);
+    ensure_complete_type(ira->codegen, src_type);
+
+    uint64_t dest_size_bytes = type_size(ira->codegen, dest_type);
+    uint64_t src_size_bytes = type_size(ira->codegen, src_type);
+    if (dest_size_bytes != src_size_bytes) {
+        ir_add_error(ira, &instruction->base,
+            buf_sprintf("destination type '%s' has size %" PRIu64 " but source type '%s' has size %" PRIu64,
+                buf_ptr(&dest_type->name), dest_size_bytes,
+                buf_ptr(&src_type->name), src_size_bytes));
+        return ira->codegen->builtin_types.entry_invalid;
+    }
+
+    if (instr_is_comptime(target) && src_type->id == dest_type->id &&
+        (src_type->id == TypeTableEntryIdPointer || src_type->id == TypeTableEntryIdMaybe))
+    {
+        ConstExprValue *val = ir_resolve_const(ira, target, UndefOk);
+        if (!val)
+            return ira->codegen->builtin_types.entry_invalid;
+
+        ConstExprValue *out_val = ir_build_const_from(ira, &instruction->base);
+        *out_val = *val;
+        out_val->type = dest_type;
+        return dest_type;
+    }
+
+    IrInstruction *result = ir_build_bit_cast(&ira->new_irb, instruction->base.scope,
+            instruction->base.source_node, nullptr, target);
+    ir_link_new_instruction(result, &instruction->base);
+    result->value.type = dest_type;
+    return dest_type;
+}
+
 static TypeTableEntry *ir_analyze_instruction_decl_ref(IrAnalyze *ira,
         IrInstructionDeclRef *instruction)
 {
@@ -12283,7 +12299,6 @@ static TypeTableEntry *ir_analyze_instruction_decl_ref(IrAnalyze *ira,
 static TypeTableEntry *ir_analyze_instruction_nocast(IrAnalyze *ira, IrInstruction *instruction) {
     switch (instruction->id) {
         case IrInstructionIdInvalid:
-        case IrInstructionIdPointerReinterpret:
         case IrInstructionIdWidenOrShorten:
         case IrInstructionIdIntToPtr:
         case IrInstructionIdPtrToInt:
@@ -12449,6 +12464,8 @@ static TypeTableEntry *ir_analyze_instruction_nocast(IrAnalyze *ira, IrInstructi
             return ir_analyze_instruction_decl_ref(ira, (IrInstructionDeclRef *)instruction);
         case IrInstructionIdPanic:
             return ir_analyze_instruction_panic(ira, (IrInstructionPanic *)instruction);
+        case IrInstructionIdBitCast:
+            return ir_analyze_instruction_bit_cast(ira, (IrInstructionBitCast *)instruction);
         case IrInstructionIdMaybeWrap:
         case IrInstructionIdErrWrapCode:
         case IrInstructionIdErrWrapPayload:
@@ -12620,7 +12637,7 @@ bool ir_has_side_effects(IrInstruction *instruction) {
         case IrInstructionIdFnProto:
         case IrInstructionIdTestComptime:
         case IrInstructionIdInitEnum:
-        case IrInstructionIdPointerReinterpret:
+        case IrInstructionIdBitCast:
         case IrInstructionIdWidenOrShorten:
         case IrInstructionIdPtrToInt:
         case IrInstructionIdIntToPtr:
diff --git a/src/ir_print.cpp b/src/ir_print.cpp
index 376de228d2..9446be43bd 100644
--- a/src/ir_print.cpp
+++ b/src/ir_print.cpp
@@ -765,9 +765,9 @@ static void ir_print_init_enum(IrPrint *irp, IrInstructionInitEnum *instruction)
     fprintf(irp->f, "}");
 }
 
-static void ir_print_pointer_reinterpret(IrPrint *irp, IrInstructionPointerReinterpret *instruction) {
-    fprintf(irp->f, "@pointerReinterpret(");
-    ir_print_other_instruction(irp, instruction->ptr);
+static void ir_print_bit_cast(IrPrint *irp, IrInstructionBitCast *instruction) {
+    fprintf(irp->f, "@bitcast(");
+    ir_print_other_instruction(irp, instruction->target);
     fprintf(irp->f, ")");
 }
 
@@ -1098,8 +1098,8 @@ static void ir_print_instruction(IrPrint *irp, IrInstruction *instruction) {
         case IrInstructionIdInitEnum:
             ir_print_init_enum(irp, (IrInstructionInitEnum *)instruction);
             break;
-        case IrInstructionIdPointerReinterpret:
-            ir_print_pointer_reinterpret(irp, (IrInstructionPointerReinterpret *)instruction);
+        case IrInstructionIdBitCast:
+            ir_print_bit_cast(irp, (IrInstructionBitCast *)instruction);
             break;
         case IrInstructionIdWidenOrShorten:
             ir_print_widen_or_shorten(irp, (IrInstructionWidenOrShorten *)instruction);
diff --git a/src/main.cpp b/src/main.cpp
index 2705dcbf4a..6f712c0f6a 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -19,46 +19,48 @@
 static int usage(const char *arg0) {
     fprintf(stderr, "Usage: %s [command] [options]\n"
         "Commands:\n"
-        "  build [sources]              create executable, object, or library from source\n"
-        "  test [sources]               create and run a test build\n"
+        "  build                        build project from build.zig\n"
+        "  build_exe [source]           create executable from source\n"
+        "  build_lib [source]           create library from source\n"
+        "  build_obj [source]           create object from source\n"
         "  parseh [source]              convert a c header file to zig extern declarations\n"
-        "  version                      print version number and exit\n"
         "  targets                      list available compilation targets\n"
+        "  test [source]                create and run a test build\n"
+        "  version                      print version number and exit\n"
         "Options:\n"
+        "  --ar-path [path]             set the path to ar\n"
+        "  --color [auto|off|on]        enable or disable colored error messages\n"
+        "  --dynamic-linker [path]      set the path to ld.so\n"
+        "  --each-lib-rpath             add rpath for each used dynamic library\n"
+        "  --ld-path [path]             set the path to the linker\n"
+        "  --libc-include-dir [path]    directory where libc stdlib.h resides\n"
+        "  --libc-lib-dir [path]        directory where libc crt1.o resides\n"
+        "  --libc-static-lib-dir [path] directory where libc crtbegin.o resides\n"
+        "  --library [lib]              link against lib\n"
+        "  --library-path [dir]         add a directory to the library search path\n"
+        "  --linker-script [path]       use a custom linker script\n"
+        "  --name [name]                override output name\n"
+        "  --output [file]              override destination path\n"
         "  --release                    build with optimizations on and debug protection off\n"
         "  --static                     output will be statically linked\n"
         "  --strip                      exclude debug symbols\n"
-        "  --export [exe|lib|obj]       override output type\n"
-        "  --name [name]                override output name\n"
-        "  --output [file]              override destination path\n"
-        "  --verbose                    turn on compiler debug output\n"
-        "  --color [auto|off|on]        enable or disable colored error messages\n"
-        "  --libc-lib-dir [path]        directory where libc crt1.o resides\n"
-        "  --libc-static-lib-dir [path] directory where libc crtbegin.o resides\n"
-        "  --libc-include-dir [path]    directory where libc stdlib.h resides\n"
-        "  --zig-std-dir [path]         directory where zig standard library resides\n"
-        "  --dynamic-linker [path]      set the path to ld.so\n"
-        "  --ld-path [path]             set the path to the linker\n"
-        "  --ar-path [path]             set the path to ar\n"
-        "  -isystem [dir]               add additional search path for other .h files\n"
-        "  -dirafter [dir]              same as -isystem but do it last\n"
-        "  --library-path [dir]         add a directory to the library search path\n"
-        "  -L[dir]                      alias for --library-path\n"
-        "  --library [lib]              link against lib\n"
         "  --target-arch [name]         specify target architecture\n"
-        "  --target-os [name]           specify target operating system\n"
         "  --target-environ [name]      specify target environment\n"
-        "  -mwindows                    (windows only) --subsystem windows to the linker\n"
-        "  -mconsole                    (windows only) --subsystem console to the linker\n"
-        "  -municode                    (windows only) link with unicode\n"
-        "  -mlinker-version [ver]       (darwin only) override linker version\n"
-        "  -rdynamic                    add all symbols to the dynamic symbol table\n"
-        "  -mmacosx-version-min [ver]   (darwin only) set Mac OS X deployment target\n"
-        "  -mios-version-min [ver]      (darwin only) set iOS deployment target\n"
+        "  --target-os [name]           specify target operating system\n"
+        "  --verbose                    turn on compiler debug output\n"
+        "  --zig-std-dir [path]         directory where zig standard library resides\n"
+        "  -L[dir]                      alias for --library-path\n"
+        "  -dirafter [dir]              same as -isystem but do it last\n"
         "  -framework [name]            (darwin only) link against framework\n"
-        "  --linker-script [path]       use a custom linker script\n"
+        "  -isystem [dir]               add additional search path for other .h files\n"
+        "  -mconsole                    (windows only) --subsystem console to the linker\n"
+        "  -mios-version-min [ver]      (darwin only) set iOS deployment target\n"
+        "  -mlinker-version [ver]       (darwin only) override linker version\n"
+        "  -mmacosx-version-min [ver]   (darwin only) set Mac OS X deployment target\n"
+        "  -municode                    (windows only) link with unicode\n"
+        "  -mwindows                    (windows only) --subsystem windows to the linker\n"
+        "  -rdynamic                    add all symbols to the dynamic symbol table\n"
         "  -rpath [path]                add directory to the runtime library search path\n"
-        "  --each-lib-rpath             add rpath for each used dynamic library\n"
     , arg0);
     return EXIT_FAILURE;
 }
@@ -144,6 +146,62 @@ int main(int argc, char **argv) {
     ZigList<const char *> rpath_list = {0};
     bool each_lib_rpath = false;
 
+    if (argc >= 2 && strcmp(argv[1], "build") == 0) {
+        const char *zig_exe_path = arg0;
+
+        init_all_targets();
+
+        Buf *zig_std_dir = buf_create_from_str(ZIG_STD_DIR);
+        Buf *special_dir = buf_alloc();
+        os_path_join(zig_std_dir, buf_sprintf("special"), special_dir);
+
+        Buf *build_runner_path = buf_alloc();
+        os_path_join(special_dir, buf_create_from_str("build_runner.zig"), build_runner_path);
+
+        ZigList<const char *> args = {0};
+        args.append(zig_exe_path);
+        for (int i = 2; i < argc; i += 1) {
+            if (strcmp(argv[i], "--verbose") == 0) {
+                verbose = true;
+                args.append(argv[i]);
+            } else {
+                args.append(argv[i]);
+            }
+        }
+
+
+        Buf root_source_dir = BUF_INIT;
+        Buf root_source_code = BUF_INIT;
+        Buf root_source_name = BUF_INIT;
+        os_path_split(build_runner_path, &root_source_dir, &root_source_name);
+        if ((err = os_fetch_file_path(build_runner_path, &root_source_code))) {
+            fprintf(stderr, "unable to open '%s': %s\n", buf_ptr(build_runner_path), err_str(err));
+            return 1;
+        }
+        CodeGen *g = codegen_create(&root_source_dir, nullptr);
+        codegen_set_out_name(g, buf_create_from_str("build"));
+        codegen_set_out_type(g, OutTypeExe);
+        codegen_set_verbose(g, verbose);
+
+        PackageTableEntry *build_pkg = new_package(".", "build.zig");
+        build_pkg->package_table.put(buf_create_from_str("std"), g->std_package);
+        g->root_package->package_table.put(buf_create_from_str("@build"), build_pkg);
+        codegen_add_root_code(g, &root_source_dir, &root_source_name, &root_source_code);
+        codegen_link(g, "build");
+
+        Termination term;
+        os_spawn_process("./build", args, &term);
+        if (term.how != TerminationIdClean || term.code != 0) {
+            fprintf(stderr, "\nBuild failed. Use the following command to reproduce the failure:\n");
+            fprintf(stderr, "./build");
+            for (size_t i = 0; i < args.length; i += 1) {
+                fprintf(stderr, " \"%s\"", args.at(i));
+            }
+            fprintf(stderr, "\n");
+        }
+        return (term.how == TerminationIdClean) ? term.code : -1;
+    }
+
     for (int i = 1; i < argc; i += 1) {
         char *arg = argv[i];
 
@@ -177,16 +235,6 @@ int main(int argc, char **argv) {
                     return usage(arg0);
                 } else if (strcmp(arg, "--output") == 0) {
                     out_file = argv[i];
-                } else if (strcmp(arg, "--export") == 0) {
-                    if (strcmp(argv[i], "exe") == 0) {
-                        out_type = OutTypeExe;
-                    } else if (strcmp(argv[i], "lib") == 0) {
-                        out_type = OutTypeLib;
-                    } else if (strcmp(argv[i], "obj") == 0) {
-                        out_type = OutTypeObj;
-                    } else {
-                        return usage(arg0);
-                    }
                 } else if (strcmp(arg, "--color") == 0) {
                     if (strcmp(argv[i], "auto") == 0) {
                         color = ErrColorAuto;
@@ -243,8 +291,15 @@ int main(int argc, char **argv) {
                 }
             }
         } else if (cmd == CmdInvalid) {
-            if (strcmp(arg, "build") == 0) {
+            if (strcmp(arg, "build_exe") == 0) {
                 cmd = CmdBuild;
+                out_type = OutTypeExe;
+            } else if (strcmp(arg, "build_obj") == 0) {
+                cmd = CmdBuild;
+                out_type = OutTypeObj;
+            } else if (strcmp(arg, "build_lib") == 0) {
+                cmd = CmdBuild;
+                out_type = OutTypeLib;
             } else if (strcmp(arg, "version") == 0) {
                 cmd = CmdVersion;
             } else if (strcmp(arg, "parseh") == 0) {
@@ -285,15 +340,7 @@ int main(int argc, char **argv) {
             if (!in_file)
                 return usage(arg0);
 
-            if (cmd == CmdBuild && !out_name) {
-                fprintf(stderr, "--name [name] not provided\n\n");
-                return usage(arg0);
-            }
-
-            if (cmd == CmdBuild && out_type == OutTypeUnknown) {
-                fprintf(stderr, "--export [exe|lib|obj] not provided\n\n");
-                return usage(arg0);
-            }
+            assert(cmd != CmdBuild || out_type != OutTypeUnknown);
 
             init_all_targets();
 
@@ -331,6 +378,9 @@ int main(int argc, char **argv) {
             Buf root_source_dir = BUF_INIT;
             Buf root_source_code = BUF_INIT;
             Buf root_source_name = BUF_INIT;
+
+            Buf *buf_out_name = (cmd == CmdTest) ? buf_create_from_str("test") :
+                (out_name == nullptr) ? nullptr : buf_create_from_str(out_name);
             if (buf_eql_str(&in_file_buf, "-")) {
                 os_get_cwd(&root_source_dir);
                 if ((err = os_fetch_file(stdin, &root_source_code))) {
@@ -338,12 +388,24 @@ int main(int argc, char **argv) {
                     return 1;
                 }
                 buf_init_from_str(&root_source_name, "");
+
             } else {
                 os_path_split(&in_file_buf, &root_source_dir, &root_source_name);
                 if ((err = os_fetch_file_path(buf_create_from_str(in_file), &root_source_code))) {
                     fprintf(stderr, "unable to open '%s': %s\n", in_file, err_str(err));
                     return 1;
                 }
+
+                if (cmd == CmdBuild && buf_out_name == nullptr) {
+                    buf_out_name = buf_alloc();
+                    Buf ext_name = BUF_INIT;
+                    os_path_extname(&root_source_name, buf_out_name, &ext_name);
+                }
+            }
+
+            if (cmd == CmdBuild && buf_out_name == nullptr) {
+                fprintf(stderr, "--name [name] not provided and unable to infer\n\n");
+                return usage(arg0);
             }
 
             CodeGen *g = codegen_create(&root_source_dir, target);
@@ -361,11 +423,7 @@ int main(int argc, char **argv) {
             } else if (cmd == CmdTest) {
                 codegen_set_out_type(g, OutTypeExe);
             }
-            if (out_name) {
-                codegen_set_out_name(g, buf_create_from_str(out_name));
-            } else if (cmd == CmdTest) {
-                codegen_set_out_name(g, buf_create_from_str("test"));
-            }
+            codegen_set_out_name(g, buf_out_name);
             if (libc_lib_dir)
                 codegen_set_libc_lib_dir(g, buf_create_from_str(libc_lib_dir));
             if (libc_static_lib_dir)
diff --git a/src/os.cpp b/src/os.cpp
index 391a9df7b4..59561398c7 100644
--- a/src/os.cpp
+++ b/src/os.cpp
@@ -139,6 +139,32 @@ void os_path_split(Buf *full_path, Buf *out_dirname, Buf *out_basename) {
     if (out_basename) buf_init_from_buf(out_basename, full_path);
 }
 
+void os_path_extname(Buf *full_path, Buf *out_basename, Buf *out_extname) {
+    if (buf_len(full_path) == 0) {
+        buf_init_from_str(out_basename, "");
+        buf_init_from_str(out_extname, "");
+        return;
+    }
+    size_t i = buf_len(full_path) - 1;
+    while (true) {
+        if (buf_ptr(full_path)[i] == '.') {
+            buf_resize(out_basename, 0);
+            buf_append_mem(out_basename, buf_ptr(full_path), i);
+
+            buf_resize(out_extname, 0);
+            buf_append_mem(out_extname, buf_ptr(full_path) + i, buf_len(full_path) - i);
+            return;
+        }
+
+        if (i == 0) {
+            buf_init_from_buf(out_basename, full_path);
+            buf_init_from_str(out_extname, "");
+            return;
+        }
+        i -= 1;
+    }
+}
+
 void os_path_join(Buf *dirname, Buf *basename, Buf *out_full_path) {
     buf_init_from_buf(out_full_path, dirname);
     uint8_t c = *(buf_ptr(out_full_path) + buf_len(out_full_path) - 1);
diff --git a/src/os.hpp b/src/os.hpp
index 1b2649a4ef..c84720fc38 100644
--- a/src/os.hpp
+++ b/src/os.hpp
@@ -34,6 +34,7 @@ int os_exec_process(const char *exe, ZigList<const char *> &args,
 
 void os_path_dirname(Buf *full_path, Buf *out_dirname);
 void os_path_split(Buf *full_path, Buf *out_dirname, Buf *out_basename);
+void os_path_extname(Buf *full_path, Buf *out_basename, Buf *out_extname);
 void os_path_join(Buf *dirname, Buf *basename, Buf *out_full_path);
 int os_path_real(Buf *rel_path, Buf *out_abs_path);
 void os_path_resolve(Buf *ref_path, Buf *target_path, Buf *out_abs_path);
diff --git a/std/build.zig b/std/build.zig
new file mode 100644
index 0000000000..746800668a
--- /dev/null
+++ b/std/build.zig
@@ -0,0 +1,59 @@
+const io = @import("io.zig");
+const mem = @import("mem.zig");
+const debug = @import("debug.zig");
+const List = @import("list.zig").List;
+const Allocator = @import("mem.zig").Allocator;
+
+error ExtraArg;
+
+pub const Builder = struct {
+    zig_exe: []const u8,
+    allocator: &Allocator,
+    exe_list: List(&Exe),
+
+    pub fn init(zig_exe: []const u8, allocator: &Allocator) -> Builder {
+        Builder {
+            .zig_exe = zig_exe,
+            .allocator = allocator,
+            .exe_list = List(&Exe).init(allocator),
+        }
+    }
+
+    pub fn addExe(self: &Builder, root_src: []const u8, name: []const u8) -> &Exe {
+        return self.addExeErr(root_src, name) %% |err| handleErr(err);
+    }
+
+    pub fn addExeErr(self: &Builder, root_src: []const u8, name: []const u8) -> %&Exe {
+        const exe = %return self.allocator.create(Exe);
+        *exe = Exe {
+            .root_src = root_src,
+            .name = name,
+        };
+        %return self.exe_list.append(exe);
+        return exe;
+    }
+
+    pub fn make(self: &Builder, args: []const []const u8) -> %void {
+        var verbose = false;
+        for (args) |arg| {
+            if (mem.eql(u8, arg, "--verbose")) {
+                verbose = true;
+            } else {
+                %%io.stderr.printf("Unrecognized argument: '{}'\n", arg);
+                return error.ExtraArg;
+            }
+        }
+        for (self.exe_list.toSlice()) |exe| {
+            %%io.stderr.printf("TODO: invoke this command:\nzig build_exe {} --name {}\n", exe.root_src, exe.name);
+        }
+    }
+};
+
+const Exe = struct {
+    root_src: []const u8,
+    name: []const u8,
+};
+
+fn handleErr(err: error) -> noreturn {
+    debug.panic("error: {}\n", @errorName(err));
+}
diff --git a/std/debug.zig b/std/debug.zig
index 2fff730a93..cc0583dd45 100644
--- a/std/debug.zig
+++ b/std/debug.zig
@@ -15,7 +15,7 @@ pub fn assert(ok: bool) {
 
 var panicking = false;
 /// This is the default panic implementation.
-pub coldcc fn panic(message: []const u8) -> noreturn {
+pub coldcc fn panic(comptime format: []const u8, args: ...) -> noreturn {
     // TODO
     // if (@atomicRmw(AtomicOp.XChg, &panicking, true, AtomicOrder.SeqCst)) { }
     if (panicking) {
@@ -28,7 +28,7 @@ pub coldcc fn panic(message: []const u8) -> noreturn {
         panicking = true;
     }
 
-    %%io.stderr.printf("{}\n", message);
+    %%io.stderr.printf(format, args);
     %%printStackTrace();
 
     os.abort();
@@ -74,7 +74,7 @@ pub fn writeStackTrace(out_stream: &io.OutStream) -> %void {
                 const name = %return compile_unit.die.getAttrString(st, DW.AT_name);
 
                 %return out_stream.printf("{}  -> {}\n", return_address, name);
-                maybe_fp = *(&const ?&const u8)(fp);
+                maybe_fp = *@bitcast(&const ?&const u8, fp);
             }
         },
         ObjectFormat.coff => {
@@ -511,7 +511,6 @@ pub var global_allocator = mem.Allocator {
     .allocFn = globalAlloc,
     .reallocFn = globalRealloc,
     .freeFn = globalFree,
-    .context = null,
 };
 
 var some_mem: [100 * 1024]u8 = undefined;
diff --git a/std/hash_map.zig b/std/hash_map.zig
index d90cbaa7ac..5c2edb33b9 100644
--- a/std/hash_map.zig
+++ b/std/hash_map.zig
@@ -236,7 +236,7 @@ test "basicHashMapTest" {
 }
 
 fn hash_i32(x: i32) -> u32 {
-    *(&u32)(&x)
+    *@bitcast(&u32, &x)
 }
 fn eql_i32(a: i32, b: i32) -> bool {
     a == b
diff --git a/std/index.zig b/std/index.zig
index 626a3749f7..dce1bdb7a5 100644
--- a/std/index.zig
+++ b/std/index.zig
@@ -1,3 +1,4 @@
+pub const build = @import("build.zig");
 pub const c = @import("c/index.zig");
 pub const cstr = @import("cstr.zig");
 pub const debug = @import("debug.zig");
diff --git a/std/mem.zig b/std/mem.zig
index 3c99029a39..f118a280e1 100644
--- a/std/mem.zig
+++ b/std/mem.zig
@@ -7,12 +7,10 @@ pub const Cmp = math.Cmp;
 
 error NoMem;
 
-pub type Context = u8;
 pub const Allocator = struct {
     allocFn: fn (self: &Allocator, n: usize) -> %[]u8,
     reallocFn: fn (self: &Allocator, old_mem: []u8, new_size: usize) -> %[]u8,
     freeFn: fn (self: &Allocator, mem: []u8),
-    context: ?&Context,
 
     /// Aborts the program if an allocation fails.
     fn checkedAlloc(self: &Allocator, comptime T: type, n: usize) -> []T {
@@ -22,6 +20,14 @@ pub const Allocator = struct {
         }
     }
 
+    fn create(self: &Allocator, comptime T: type) -> %&T {
+        &(%return self.alloc(T, 1))[0]
+    }
+
+    fn destroy(self: &Allocator, ptr: var) {
+        self.free(ptr[0...1]);
+    }
+
     fn alloc(self: &Allocator, comptime T: type, n: usize) -> %[]T {
         const byte_count = %return math.mulOverflow(usize, @sizeOf(T), n);
         ([]T)(%return self.allocFn(self, byte_count))
@@ -37,6 +43,62 @@ pub const Allocator = struct {
     }
 };
 
+pub const IncrementingAllocator = struct {
+    allocator: Allocator,
+    bytes: []u8,
+    end_index: usize,
+
+    fn init(capacity: usize) -> %IncrementingAllocator {
+        switch (@compileVar("os")) {
+            Os.linux, Os.darwin, Os.macosx, Os.ios => {
+                const p = os.posix;
+                const addr = p.mmap(null, capacity, p.PROT_READ|p.PROT_WRITE,
+                    p.MAP_PRIVATE|p.MAP_ANONYMOUS|p.MAP_NORESERVE, -1, 0);
+                if (addr == p.MAP_FAILED) {
+                    return error.NoMem;
+                }
+                return IncrementingAllocator {
+                    .allocator = Allocator {
+                        .allocFn = alloc,
+                        .reallocFn = realloc,
+                        .freeFn = free,
+                    },
+                    .bytes = (&u8)(addr)[0...capacity],
+                    .end_index = 0,
+                };
+            },
+            else => @compileError("Unsupported OS"),
+        }
+    }
+
+    fn deinit(self: &IncrementingAllocator) {
+        _ = os.posix.munmap(self.bytes.ptr, self.bytes.len);
+    }
+
+    fn alloc(allocator: &Allocator, n: usize) -> %[]u8 {
+        // TODO
+        //const self = @fieldParentPtr(IncrementingAllocator, "allocator", allocator);
+        const self = @bitcast(&IncrementingAllocator, allocator);
+        const new_end_index = self.end_index + n;
+        if (new_end_index > self.bytes.len) {
+            return error.NoMem;
+        }
+        const result = self.bytes[self.end_index...new_end_index];
+        self.end_index = new_end_index;
+        return result;
+    }
+
+    fn realloc(allocator: &Allocator, old_mem: []u8, new_size: usize) -> %[]u8 {
+        const result = %return alloc(allocator, new_size);
+        copy(u8, result, old_mem);
+        return result;
+    }
+
+    fn free(allocator: &Allocator, bytes: []u8) {
+        // Do nothing. That's the point of an incrementing allocator.
+    }
+};
+
 /// Copy all of source into dest at position 0.
 /// dest.len must be >= source.len.
 pub fn copy(comptime T: type, dest: []T, source: []const T) {
diff --git a/std/os/linux.zig b/std/os/linux.zig
index be86136dee..0e616cfc53 100644
--- a/std/os/linux.zig
+++ b/std/os/linux.zig
@@ -5,16 +5,29 @@ const arch = switch (@compileVar("arch")) {
 };
 const errno = @import("errno.zig");
 
-pub const MMAP_PROT_NONE =  0;
-pub const MMAP_PROT_READ =  1;
-pub const MMAP_PROT_WRITE = 2;
-pub const MMAP_PROT_EXEC =  4;
+pub const PROT_NONE      = 0;
+pub const PROT_READ      = 1;
+pub const PROT_WRITE     = 2;
+pub const PROT_EXEC      = 4;
+pub const PROT_GROWSDOWN = 0x01000000;
+pub const PROT_GROWSUP   = 0x02000000;
 
-pub const MMAP_MAP_FILE =    0;
-pub const MMAP_MAP_SHARED =  1;
-pub const MMAP_MAP_PRIVATE = 2;
-pub const MMAP_MAP_FIXED =   16;
-pub const MMAP_MAP_ANON =    32;
+pub const MAP_FAILED     = @maxValue(usize);
+pub const MAP_SHARED     = 0x01;
+pub const MAP_PRIVATE    = 0x02;
+pub const MAP_TYPE       = 0x0f;
+pub const MAP_FIXED      = 0x10;
+pub const MAP_ANONYMOUS  = 0x20;
+pub const MAP_NORESERVE  = 0x4000;
+pub const MAP_GROWSDOWN  = 0x0100;
+pub const MAP_DENYWRITE  = 0x0800;
+pub const MAP_EXECUTABLE = 0x1000;
+pub const MAP_LOCKED     = 0x2000;
+pub const MAP_POPULATE   = 0x8000;
+pub const MAP_NONBLOCK   = 0x10000;
+pub const MAP_STACK      = 0x20000;
+pub const MAP_HUGETLB    = 0x40000;
+pub const MAP_FILE       = 0;
 
 pub const SIGHUP    = 1;
 pub const SIGINT    = 2;
@@ -226,7 +239,7 @@ pub const AF_MAX = PF_MAX;
 
 /// Get the errno from a syscall return value, or 0 for no error.
 pub fn getErrno(r: usize) -> usize {
-    const signed_r = *(&isize)(&r);
+    const signed_r = *@bitcast(&isize, &r);
     if (signed_r > -4096 and signed_r < 0) usize(-signed_r) else 0
 }
 
diff --git a/std/special/build_runner.zig b/std/special/build_runner.zig
new file mode 100644
index 0000000000..73a608487a
--- /dev/null
+++ b/std/special/build_runner.zig
@@ -0,0 +1,18 @@
+const root = @import("@build");
+const std = @import("std");
+const io = std.io;
+const Builder = std.build.Builder;
+const mem = std.mem;
+
+pub fn main(args: [][]u8) -> %void {
+    const zig_exe = args[1];
+    const leftover_args = args[2...];
+
+    // TODO use a more general purpose allocator here
+    var inc_allocator = %%mem.IncrementingAllocator.init(10 * 1024 * 1024);
+    defer inc_allocator.deinit();
+
+    var builder = Builder.init(zig_exe, &inc_allocator.allocator);
+    root.build(&builder);
+    %return builder.make(leftover_args);
+}
diff --git a/std/special/compiler_rt.zig b/std/special/compiler_rt.zig
index 8f61876305..f5c83becc7 100644
--- a/std/special/compiler_rt.zig
+++ b/std/special/compiler_rt.zig
@@ -15,7 +15,7 @@ export fn __udivdi3(a: du_int, b: du_int) -> du_int {
 
 fn du_int_to_udwords(x: du_int) -> udwords {
     @setDebugSafety(this, false);
-    return *(&udwords)(&x);
+    return *@bitcast(&udwords, &x);
 }
 
 export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
@@ -66,7 +66,7 @@ export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
             if (var rem ?= maybe_rem) {
                 r[high] = n[high] % d[high];
                 r[low] = 0;
-                *rem = *(&du_int)(&r[0]);
+                *rem = *@bitcast(&du_int, &r[0]);
             }
             return n[high] / d[high];
         }
@@ -78,7 +78,7 @@ export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
             if (var rem ?= maybe_rem) {
                 r[low] = n[low];
                 r[high] = n[high] & (d[high] - 1);
-                *rem = *(&du_int)(&r[0]);
+                *rem = *@bitcast(&du_int, &r[0]);
             }
             return n[high] >> @ctz(d[high]);
         }
@@ -89,7 +89,7 @@ export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
         // 0 <= sr <= n_uword_bits - 2 or sr large
         if (sr > n_uword_bits - 2) {
             if (var rem ?= maybe_rem) {
-                *rem = *(&du_int)(&n[0]);
+                *rem = *@bitcast(&du_int, &n[0]);
             }
             return 0;
         }
@@ -113,12 +113,12 @@ export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
                     *rem = n[low] & (d[low] - 1);
                 }
                 if (d[low] == 1) {
-                    return *(&du_int)(&n[0]);
+                    return *@bitcast(&du_int, &n[0]);
                 }
                 sr = @ctz(d[low]);
                 q[high] = n[high] >> sr;
                 q[low] = (n[high] << (n_uword_bits - sr)) | (n[low] >> sr);
-                return *(&du_int)(&q[0]);
+                return *@bitcast(&du_int, &q[0]);
             }
             // K X
             // ---
@@ -154,7 +154,7 @@ export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
             // 0 <= sr <= n_uword_bits - 1 or sr large
             if (sr > n_uword_bits - 1) {
                 if (var rem ?= maybe_rem) {
-                    *rem = *(&du_int)(&n[0]);
+                    *rem = *@bitcast(&du_int, &n[0]);
                 }
                 return 0;
             }
@@ -191,17 +191,17 @@ export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
         //      r.all -= d.all;
         //      carry = 1;
         // }
-        const s: di_int = (di_int)(*(&du_int)(&d[0]) - *(&du_int)(&r[0]) - 1) >> (n_udword_bits - 1);
+        const s: di_int = (di_int)(*@bitcast(&du_int, &d[0]) - *@bitcast(&du_int, &r[0]) - 1) >> (n_udword_bits - 1);
         carry = su_int(s & 1);
-        *(&du_int)(&r[0]) -= *(&du_int)(&d[0]) & u64(s);
+        *@bitcast(&du_int, &r[0]) -= *@bitcast(&du_int, &d[0]) & u64(s);
 
         sr -= 1;
     }
-    *(&du_int)(&q[0]) = (*(&du_int)(&q[0]) << 1) | u64(carry);
+    *@bitcast(&du_int, &q[0]) = (*@bitcast(&du_int, &q[0]) << 1) | u64(carry);
     if (var rem ?= maybe_rem) {
-        *rem = *(&du_int)(&r[0]);
+        *rem = *@bitcast(&du_int, &r[0]);
     }
-    return *(&du_int)(&q[0]);
+    return *@bitcast(&du_int, &q[0]);
 }
 
 export fn __umoddi3(a: du_int, b: du_int) -> du_int {
diff --git a/std/special/zigrt.zig b/std/special/zigrt.zig
index 148516eb40..6f7911917d 100644
--- a/std/special/zigrt.zig
+++ b/std/special/zigrt.zig
@@ -1,5 +1,5 @@
 // This file contains functions that zig depends on to coordinate between
-// multiple .o files. The symbols are defined LinkOnce so that multiple
+// multiple .o files. The symbols are defined Weak so that multiple
 // instances of zig_rt.zig do not conflict with each other.
 
 export coldcc fn __zig_panic(message_ptr: &const u8, message_len: usize) -> noreturn {
@@ -11,6 +11,6 @@ export coldcc fn __zig_panic(message_ptr: &const u8, message_len: usize) -> nore
     } else if (@compileVar("os") == Os.freestanding) {
         while (true) {}
     } else {
-        @import("std").debug.panic(message_ptr[0...message_len]);
+        @import("std").debug.panic("{}\n", message_ptr[0...message_len]);
     }
 }
diff --git a/test/cases/cast.zig b/test/cases/cast.zig
index 928b631339..7f97e6660b 100644
--- a/test/cases/cast.zig
+++ b/test/cases/cast.zig
@@ -15,7 +15,18 @@ test "numLitIntToPtrCast" {
 test "pointerReinterpretConstFloatToInt" {
     const float: f64 = 5.99999999999994648725e-01;
     const float_ptr = &float;
-    const int_ptr = (&i32)(float_ptr);
+    const int_ptr = @bitcast(&i32, float_ptr);
     const int_val = *int_ptr;
     assert(int_val == 858993411);
 }
+
+test "implicitly cast a pointer to a const pointer of it" {
+    var x: i32 = 1;
+    const xp = &x;
+    funcWithConstPtrPtr(xp);
+    assert(x == 2);
+}
+
+fn funcWithConstPtrPtr(x: &const &i32) {
+    **x += 1;
+}
diff --git a/test/cases/eval.zig b/test/cases/eval.zig
index b1d10ca8bf..0d52985329 100644
--- a/test/cases/eval.zig
+++ b/test/cases/eval.zig
@@ -284,3 +284,18 @@ fn testCompTimeUIntComparisons(x: u32) {
         @compileError("this condition should be comptime known");
     }
 }
+
+
+
+test "const ptr to variable data changes at runtime" {
+    assert(foo_ref.name[0] == 'a');
+    foo_ref.name = "b";
+    assert(foo_ref.name[0] == 'b');
+}
+
+const Foo = struct {
+    name: []const u8,
+};
+
+var foo_contents = Foo { .name = "a", };
+const foo_ref = &foo_contents;
diff --git a/test/cases/generics.zig b/test/cases/generics.zig
index c23b189dc3..68637c614b 100644
--- a/test/cases/generics.zig
+++ b/test/cases/generics.zig
@@ -121,5 +121,5 @@ test "genericFnWithImplicitCast" {
 }
 fn getByte(ptr: ?&const u8) -> u8 {*??ptr}
 fn getFirstByte(comptime T: type, mem: []const T) -> u8 {
-    getByte((&const u8)(&mem[0]))
+    getByte(@bitcast(&const u8, &mem[0]))
 }
diff --git a/test/cases/misc.zig b/test/cases/misc.zig
index c26ae8b04a..81b9db3a24 100644
--- a/test/cases/misc.zig
+++ b/test/cases/misc.zig
@@ -246,15 +246,15 @@ test "typeEquality" {
 
 const global_a: i32 = 1234;
 const global_b: &const i32 = &global_a;
-const global_c: &const f32 = (&const f32)(global_b);
+const global_c: &const f32 = @bitcast(&const f32, global_b);
 test "compileTimeGlobalReinterpret" {
-    const d = (&const i32)(global_c);
+    const d = @bitcast(&const i32, global_c);
     assert(*d == 1234);
 }
 
 test "explicitCastMaybePointers" {
     const a: ?&i32 = undefined;
-    const b: ?&f32 = (?&f32)(a);
+    const b: ?&f32 = @bitcast(?&f32, a);
 }
 
 test "genericMallocFree" {
@@ -263,7 +263,7 @@ test "genericMallocFree" {
 }
 const some_mem : [100]u8 = undefined;
 fn memAlloc(comptime T: type, n: usize) -> %[]T {
-    return (&T)(&some_mem[0])[0...n];
+    return @bitcast(&T, &some_mem[0])[0...n];
 }
 fn memFree(comptime T: type, memory: []T) { }
 
diff --git a/test/cases/struct.zig b/test/cases/struct.zig
index b927c01941..bd69177d4f 100644
--- a/test/cases/struct.zig
+++ b/test/cases/struct.zig
@@ -41,7 +41,7 @@ const VoidStructFieldsFoo = struct {
 
 test "fn" {
     var foo: StructFoo = undefined;
-    @memset((&u8)(&foo), 0, @sizeOf(StructFoo));
+    @memset(@bitcast(&u8, &foo), 0, @sizeOf(StructFoo));
     foo.a += 1;
     foo.b = foo.a == 1;
     testFoo(foo);
diff --git a/test/run_tests.cpp b/test/run_tests.cpp
index 162ba24903..b82431fae1 100644
--- a/test/run_tests.cpp
+++ b/test/run_tests.cpp
@@ -73,10 +73,8 @@ static TestCase *add_simple_case(const char *case_name, const char *source, cons
     test_case->source_files.at(0).relative_path = tmp_source_path;
     test_case->source_files.at(0).source_code = source;
 
-    test_case->compiler_args.append("build");
+    test_case->compiler_args.append("build_exe");
     test_case->compiler_args.append(tmp_source_path);
-    test_case->compiler_args.append("--export");
-    test_case->compiler_args.append("exe");
     test_case->compiler_args.append("--name");
     test_case->compiler_args.append("test");
     test_case->compiler_args.append("--output");
@@ -113,15 +111,12 @@ static TestCase *add_compile_fail_case(const char *case_name, const char *source
         test_case->compile_errors.append(arg);
     }
 
-    test_case->compiler_args.append("build");
+    test_case->compiler_args.append("build_obj");
     test_case->compiler_args.append(tmp_source_path);
 
     test_case->compiler_args.append("--name");
     test_case->compiler_args.append("test");
 
-    test_case->compiler_args.append("--export");
-    test_case->compiler_args.append("obj");
-
     test_case->compiler_args.append("--output");
     test_case->compiler_args.append(tmp_exe_path);
 
@@ -142,15 +137,12 @@ static void add_debug_safety_case(const char *case_name, const char *source) {
         test_case->source_files.at(0).relative_path = tmp_source_path;
         test_case->source_files.at(0).source_code = source;
 
-        test_case->compiler_args.append("build");
+        test_case->compiler_args.append("build_exe");
         test_case->compiler_args.append(tmp_source_path);
 
         test_case->compiler_args.append("--name");
         test_case->compiler_args.append("test");
 
-        test_case->compiler_args.append("--export");
-        test_case->compiler_args.append("exe");
-
         test_case->compiler_args.append("--output");
         test_case->compiler_args.append(tmp_exe_path);
 
@@ -164,15 +156,12 @@ static void add_debug_safety_case(const char *case_name, const char *source) {
         test_case->source_files.at(0).source_code = source;
         test_case->output = "";
 
-        test_case->compiler_args.append("build");
+        test_case->compiler_args.append("build_exe");
         test_case->compiler_args.append(tmp_source_path);
 
         test_case->compiler_args.append("--name");
         test_case->compiler_args.append("test");
 
-        test_case->compiler_args.append("--export");
-        test_case->compiler_args.append("exe");
-
         test_case->compiler_args.append("--output");
         test_case->compiler_args.append(tmp_exe_path);
 
@@ -471,8 +460,8 @@ const foo : i32 = 0;
 const c = @cImport(@cInclude("stdlib.h"));
 
 export fn compare_fn(a: ?&const c_void, b: ?&const c_void) -> c_int {
-    const a_int = (&i32)(a ?? unreachable);
-    const b_int = (&i32)(b ?? unreachable);
+    const a_int = @bitcast(&i32, a ?? unreachable);
+    const b_int = @bitcast(&i32, b ?? unreachable);
     if (*a_int < *b_int) {
         -1
     } else if (*a_int > *b_int) {
@@ -485,7 +474,7 @@ export fn compare_fn(a: ?&const c_void, b: ?&const c_void) -> c_int {
 export fn main(args: c_int, argv: &&u8) -> c_int {
     var array = []u32 { 1, 7, 3, 2, 0, 9, 4, 8, 6, 5 };
 
-    c.qsort((&c_void)(&array[0]), c_ulong(array.len), @sizeOf(i32), compare_fn);
+    c.qsort(@bitcast(&c_void, &array[0]), c_ulong(array.len), @sizeOf(i32), compare_fn);
 
     for (array) |item, i| {
         if (item != i) {