mruby-mruby/doc/guides/mrbconf.md

mruby configuration macros

How to use these macros

You can use mrbconfs with following ways:

• Write them in mrbconf.h.
  • Using compiler flags is preferred when building a cross binaries or multiple mruby binaries since it's easier to use different mrbconf per each MRuby::Build.
  • Most flags can be enabled by just commenting in.
• Pass them as compiler flags.
  • Make sure you pass the same flags to all compilers since some mrbconf(e.g., MRB_GC_FIXED_ARENA) changes struct layout and cause memory access error when C and other language(e.g., C++) is mixed.

stdio setting

MRB_NO_STDIO

• When defined <stdio.h> functions won't be used.
• Some features will be disabled when this is enabled:
  • mrb_irep load/dump from/to file.
  • Compiling mruby script from a file.
  • Printing features in src/print.c.

Debug macros

MRB_USE_DEBUG_HOOK

• When defined code fetch hook and debug OP hook will be enabled.
• When using any of the hook set function pointer code_fetch_hook and/or debug_op_hook of mrb_state.
• Fetch hook will be called before any OP.
• Debug OP hook will be called when dispatching OP_DEBUG.

MRB_DEBUG

• When defined mrb_assert* macro will be defined with macros from <assert.h>.
• Could be enabled via enable_debug method of MRuby::Build.

Stack configuration

MRB_STACK_EXTEND_DOUBLING

• If defined doubles the stack size when extending it.
• Else extends stack with MRB_STACK_GROWTH.

MRB_STACK_GROWTH

• Default value is 128.
• Used in stack extending.
• Ignored when MRB_STACK_EXTEND_DOUBLING is defined.

MRB_STACK_MAX

• Default value is 0x40000 - MRB_STACK_GROWTH.
• Raises RuntimeError when stack size exceeds this value.

Primitive type configuration

MRB_USE_FLOAT32

• When defined single precision floating-point type(C type float) is used as mrb_float.
• Otherwise, double precision floating-point type(C type double) is used as mrb_float.

MRB_NO_FLOAT

• When defined removes floating-point numbers from mruby.
• It makes mruby easier to handle in "Microcontroller without FPU" and "Kernel Space".

MRB_INT32

• When defined, or MRB_INT64 are not defined on 32-bit CPU mode, mrb_int will be defined as int32_t.
• Conflicts with MRB_INT64.

MRB_INT64

• When defined, or MRB_INT32 are not defined on 64-bit CPU mode, mrb_int will be defined as int64_t.
• Conflicts with MRB_INT32.

Garbage collector configuration

MRB_GC_STRESS

• When defined full GC is emitted per each RBasic allocation.
• Mainly used in memory manager debugging.

MRB_GC_TURN_OFF_GENERATIONAL

• When defined turns generational GC by default.

MRB_GC_FIXED_ARENA

• When defined used fixed size GC arena.
• Raises RuntimeError when this is defined and GC arena size exceeds MRB_GC_ARENA_SIZE.
• Useful tracking unnecessary mruby object allocation.

MRB_GC_ARENA_SIZE

• Default value is 100.
• Ignored when MRB_GC_FIXED_ARENA isn't defined.
• Defines fixed GC arena size.

MRB_HEAP_PAGE_SIZE

• Defines value is 1024.
• Specifies number of RBasic per each heap page.

Memory pool configuration

POOL_ALIGNMENT

• Default value is 4.
• If you're allocating data types that requires alignment more than default value define the largest value of required alignment.

POOL_PAGE_SIZE

• Default value is 16000.
• Specifies page size of pool page.
• Smaller the value is increases memory overhead.

State atexit configuration

MRB_FIXED_STATE_ATEXIT_STACK

• If defined enables fixed size mrb_state atexit stack.
• Raises RuntimeError when mrb_state_atexit call count to same mrb_state exceeds MRB_FIXED_STATE_ATEXIT_STACK_SIZE's value.

MRB_FIXED_STATE_ATEXIT_STACK_SIZE

• Default value is 5.
• If MRB_FIXED_STATE_ATEXIT_STACK isn't defined this macro is ignored.

mrb_value configuration

MRB_ENDIAN_BIG

• If defined compiles mruby for big endian machines.
• Used in MRB_NAN_BOXING.
• Some mrbgem use this mrbconf.

MRB_NAN_BOXING

• If defined represent mrb_value in boxed double.
• Conflicts with MRB_USE_FLOAT32 and MRB_NO_FLOAT.

MRB_WORD_BOXING

• If defined represent mrb_value as a word.
• If defined Float will be a mruby object with RBasic.

Reduce heap memory configuration

MRB_USE_LINK_TIME_RO_DATA_P

• Only available on ELF platforms.
• If you specify the address of a read-only section when creating a symbol or string, that string will be used as it is.
• Heap memory can be saved.
• Uses __ehdr_start and __init_array_start.
• It must be __ehdr_start < data_addr < __init_array_start.

MRB_USE_CUSTOM_RO_DATA_P

• Takes precedence over MRB_USE_LINK_TIME_RO_DATA_P.
• Please try if MRB_USE_LINK_TIME_RO_DATA_P is not available.
• The mrb_ro_data_p() function is implemented by the user in an arbitrary file.
• The prototype declaration is mrb_bool mrb_ro_data_p(const char *ptr).
• Return TRUE if ptr is in the read-only section, otherwise return FALSE.

Other configuration

MRB_UTF8_STRING

• Adds UTF-8 encoding support to character-oriented String instance methods.
• If it isn't defined, they only support the US-ASCII encoding.

MRB_FUNCALL_ARGC_MAX

• Default value is 16.
• Specifies 4th argument(argc) max value of mrb_funcall.
• Raises ArgumentError when the argc argument is bigger then this value mrb_funcall.

KHASH_DEFAULT_SIZE

• Default value is 32.
• Specifies default size of khash table bucket.
• Used in kh_init_ ## name function.

MRB_NO_METHOD_CACHE

• Disable method cache to save memory.

MRB_METHOD_CACHE_SIZE

• Default value is 256.
• Ignored if MRB_NO_METHOD_CACHE is defined.
• Need to be the power of 2.

MRB_USE_METHOD_T_STRUCT

• Use C struct to represent mrb_method_t
• No MRB_USE_METHOD_T_STRUCT requires highest 2 bits of function pointers to be zero
• Define this macro on machines that use higher bits of pointers

MRB_USE_ALL_SYMBOLS

• Make it available Symbol.all_symbols in mrbgems/mruby-symbol-ext
• Increase heap memory usage.