This is a low level specification of the Krakatau assembler syntax. For a high level introduction to the Krakatau assembler, click here.
NL represents one or more newlines, with optional comments or other whitespace. Comments begin with ; and continue until the end of the line. Places where NL appears in the grammar must have a newline. All other tokens are implicitly separated by non-NL whitespace (you can't break lines except where permitted by the grammar).
WORD:
(?:[a-zA-Z_$\(<]|\[[A-Z\[])[\w$;/\[\(\)<>*+-]*
REF:
\[[a-z0-9_]+\]
BSREF:
\[bs:[a-z0-9_]+\]
LABEL_DEF:
L\w+:
STRING_LITERAL:
b?"[^"\n\\]*(?:\\.[^"\n\\]*)*"
b?'[^'\n\\]*(?:\\.[^'\n\\]*)*'
INT_LITERAL:
[+-]?(?:0x[0-9a-fA-F]+|[1-9][0-9]*|0)
DOUBLE_LITERAL:
[+-]Infinity
[+-]NaN(?:<0x[0-9a-fA-F]+>)?
[+-]?\d+\.\d+(?:e[+-]?\d+)? // decimal float
[+-]?\d+(?:e[+-]?\d+) // decimal float without fraction (exponent mandatory)
[+-]?0x[0-9a-fA-F]+(?:\.[0-9a-fA-F]+)?(?:p[+-]?\d+) // hex float
A WORD consists of one or more ascii letters, digits, _, $, ;, /, [, (, ), <, >, *, +, or -, except that it must start with a letter, _, $, [, <, or (, and if it starts with [, the second character must be A-Z (upper case) or [. (A token with [ followed by a digit or lowercase letter is instead parsed as the BSREF or REF token type).
LONG_LITERAL has the same format as INT_LITERAL followed by an uppcercase L. FLOAT_LITERAL has the same format as DOUBLE_LITERAL followed by a lowercase f.
NaNs with a specific binary representation can be represented by suffixing with the hexadecimal value in angle brackets. For example, -NaN<0x7ff0123456789abc> or +NaN<0xFFABCDEF>f. This must have exactly 8 or 16 hex digits for float and double literals respectively.
As an example of hexidecimal float literals, the minimum positive float is 0x0.000001p-125F and the maximum negative double is -0x0.0000000000001p-1022. Likewise, the maximum denormal is 0x0.fffffffffffffp-1022.
String literals may be double or single quoted, and may be proceeded by b to indicate a raw byte string. Additionally, the permitted escape sequences are as follows: \\, \n, \r, \t, \", \', \uDDDD, \U00DDDDDD, \xDD. \u and \U are 16 and 32 bit unicode escapes respectively, and must be followed by the appropriate hex digits. \U escapes must be a legal unicode code point. \x is a byte escape and can be used to represent non-ascii byte values in raw byte strings.
The productions u8, u16, etc. rerepresent INTEGER_LITERALs with value constrained to be an 8, 16, etc. bit unsigned integer. Likewise, i8, i16, etc. represent signed integer literals.
The flags production represents zero or more of the tokens "abstract", "annotation", "bridge", "enum", "final", "interface", "mandated", "module", "native", "open", "private", "protected", "public", "static", "static_phase", "strict", "strictfp", "super", "synchronized", "synthetic", "transient", "transitive", "varargs", "volatile". Additionally, if the token following flags is a WORD, it must not be one of these values (in other words, flags is greedy).
The lbl production represents a WORD that begins with an uppercase L.
The top most production is source_file. A Krakatau assembly file can contain any number of class definitions.
source_file:
NL? class_def*
class_def:
(".version" u16 u16 NL)?
".class" flags clsref NL
".super" clsref NL
interface*
clsitem*
".end" "class" NL
interface:
".implements" clsref NL
clsitem:
".bootstrap" BSREF "=" ref_or_tagged_bootstrap NL
".const" REF "=" ref_or_tagged_const NL
field NL
method NL
attribute NL
field:
".field" flags utfref utfref ("=" ldc_rhs)? fieldattrs?
fieldattrs:
".fieldattributes" NL
(attribute NL)*
".end" "fieldattributes"
method:
".method" flags utfref ":" utfref NL
(attribute NL)*
".end" "method"
attribute:
".attribute" utfref ("length" u32)? STRING_LITERAL
".attribute" utfref ("length" u32)? attrbody
attrbody
Attributes:
attrbody:
".annotationdefault" element_value
".code" code_attr
".constantvalue" ldc_rhs
".deprecated"
".enclosing" "method" clsref natref
".exceptions" clsref*
".innerclasses" (clsref clsref utfref flags NL)* ".end" "innerclasses"
".linenumbertable" (lbl u16 NL)* ".end" "linenumbertable"
".localvariabletable" (local_var_table_item NL)* ".end" "localvariabletable"
".localvariabletypetable" (local_var_table_item NL)* ".end" "localvariabletypetable"
".methodparameters" (utfref flags NL)* ".end" "methodparameters"
".module" module
".modulemainclass" clsref
".modulepackages" single*
".nesthost" clsref
".nestmembers" clsref*
".permittedsubclasses" clsref*
".record" (recorD_item NL)* ".end" "record"
".runtime" runtime_visibility runtime_attr
".signature" utfref
".sourcedebugextension" STRING_LITERAL
".sourcefile" utfref
".stackmaptable"
".synthetic"
annotation:
annotation_sub "annotation"
annotation_sub:
utfref NL (utfref "=" element_value NL)* ".end"
element_value:
"annotation" annotation
"array" NL (element_value NL)* ".end" "array"
"boolean" ldc_rhs
"byte" ldc_rhs
"char" ldc_rhs
"class" utfref
"double" ldc_rhs
"enum" utfref utfref
"float" ldc_rhs
"int" ldc_rhs
"long" ldc_rhs
"short" ldc_rhs
"string" utfref
local_var_table_item:
u16 "is" utfref utfref "from" lbl "to" lbl
module:
utfref flags "version" utfref NL
(".requires" single flags "version" utfref NL)*
(".exports" exports_item NL)*
(".opens" exports_item NL)*
(".uses" clsref NL)*
(".provides" clsref "with" (clsref NL)* NL)*
".end" "module"
exports_item:
single flags ("to" (single NL)*)?
record_item:
utfref utfref record_attrs? NL
record_attrs:
".attributes" (attribute NL)* ".end" "attributes"
runtime_visibility:
"visible"
"invisible"
runtime_attr:
"annotations" (annotation NL)* ".end" "annotations"
"paramannotations" (param_annotation NL)* ".end" "paramannotations"
"typeannotations" (type_annotation NL)* ".end" "typeannotations"
param_annotation:
".paramannotation" NL
(annotation NL)*
".end" "paramannotation"
type_annotation:
".typeannotation" ta_target_info ta_target_path annotation_sub "typeannotation"
ta_target_info:
u8 ta_target_info_body NL
ta_target_info_body:
"typeparam" u8
"super" u16
"typeparambound" u8 u8
"empty"
"methodparam" u8
"throws" u16
"localvar" NL (localvar_info NL)* ".end" "localvar"
"catch" u16
"offset" lbl
"typearg" lbl u8
localvar_info:
"nowhere"
"from" lbl "to" lbl
ta_target_path:
".typepath" NL (u8 u8 NL)* ".end" "typepath" NL
Code:
code_attr:
"long"? "stack" u16 "locals" u16 NL
(code_item NL)*
(attribute NL)*
".end" "code"
code_item:
LABEL_DEF instruction?
instruction
code_directive
code_directive:
".catch" clsref "from" lbl "to" lbl "using" lbl
".stack" stack_map_item
stack_map_item:
"same"
"stack_1" vtype
"stack_1_extended" vtype
"chop" u8
"same_extended"
"append" vtype+
"full" NL "locals" vtype* NL "stack" vtype* NL ".end" "stack"
vtype:
"Float"
"Integer"
"Long"
"Null"
"Object" clsref
"Top"
"Uninitialized" lbl
"UninitializedThis"
Bytecode instructions:
instruction:
"aaload"
"aastore"
"aconst_null"
"aload" u8
"aload_0"
"aload_1"
"aload_2"
"aload_3"
"anewarray" clsref
"areturn"
"arraylength"
"astore" u8
"astore_0"
"astore_1"
"astore_2"
"astore_3"
"athrow"
"baload"
"bastore"
"bipush" i8
"caload"
"castore"
"checkcast" clsref
"d2f"
"d2i"
"d2l"
"dadd"
"daload"
"dastore"
"dcmpg"
"dcmpl"
"dconst_0"
"dconst_1"
"ddiv"
"dload" u8
"dload_0"
"dload_1"
"dload_2"
"dload_3"
"dmul"
"dneg"
"drem"
"dreturn"
"dstore" u8
"dstore_0"
"dstore_1"
"dstore_2"
"dstore_3"
"dsub"
"dup"
"dup2"
"dup2_x1"
"dup2_x2"
"dup_x1"
"dup_x2"
"f2d"
"f2i"
"f2l"
"fadd"
"faload"
"fastore"
"fcmpg"
"fcmpl"
"fconst_0"
"fconst_1"
"fconst_2"
"fdiv"
"fload" u8
"fload_0"
"fload_1"
"fload_2"
"fload_3"
"fmul"
"fneg"
"frem"
"freturn"
"fstore" u8
"fstore_0"
"fstore_1"
"fstore_2"
"fstore_3"
"fsub"
"getfield" ref_or_tagged_const
"getstatic" ref_or_tagged_const
"goto" lbl
"goto_w" lbl
"i2b"
"i2c"
"i2d"
"i2f"
"i2l"
"i2s"
"iadd"
"iaload"
"iand"
"iastore"
"iconst_0"
"iconst_1"
"iconst_2"
"iconst_3"
"iconst_4"
"iconst_5"
"iconst_m1"
"idiv"
"if_acmpeq" lbl
"if_acmpne" lbl
"if_icmpeq" lbl
"if_icmpge" lbl
"if_icmpgt" lbl
"if_icmple" lbl
"if_icmplt" lbl
"if_icmpne" lbl
"ifeq" lbl
"ifge" lbl
"ifgt" lbl
"ifle" lbl
"iflt" lbl
"ifne" lbl
"ifnonnull" lbl
"ifnull" lbl
"iinc" u8 i8
"iload" u8
"iload_0"
"iload_1"
"iload_2"
"iload_3"
"imul"
"ineg"
"instanceof" clsref
"invokedynamic" ref_or_tagged_const
"invokeinterface" ref_or_tagged_const u8?
"invokespecial" ref_or_tagged_const
"invokestatic" ref_or_tagged_const
"invokevirtual" ref_or_tagged_const
"ior"
"irem"
"ireturn"
"ishl"
"ishr"
"istore" u8
"istore_0"
"istore_1"
"istore_2"
"istore_3"
"isub"
"iushr"
"ixor"
"jsr" lbl
"jsr_w" lbl
"l2d"
"l2f"
"l2i"
"ladd"
"laload"
"land"
"lastore"
"lcmp"
"lconst_0"
"lconst_1"
"ldc" ldc_rhs
"ldc2_w" ldc_rhs
"ldc_w" ldc_rhs
"ldiv"
"lload" u8
"lload_0"
"lload_1"
"lload_2"
"lload_3"
"lmul"
"lneg"
"lookupswitch" lookupswitch
"lor"
"lrem"
"lreturn"
"lshl"
"lshr"
"lstore" u8
"lstore_0"
"lstore_1"
"lstore_2"
"lstore_3"
"lsub"
"lushr"
"lxor"
"monitorenter"
"monitorexit"
"multianewarray" clsref u8
"new" clsref
"newarray" ("boolean" | "char" | "float" | "double" | "byte" | "short" | "int" | "long")
"nop"
"pop"
"pop2"
"putfield" ref_or_tagged_const
"putstatic" ref_or_tagged_const
"ret" u8
"return"
"saload"
"sastore"
"sipush" i16
"swap"
"tableswitch" tableswitch
"wide" wide_instruction
lookupswitch:
NL
(i32 ":" lbl NL)*
"default" ":" lbl
tableswitch:
i32 NL
(lbl NL)+
"default" ":" lbl
wide_instruction:
"aload" u16
"astore" u16
"dload" u16
"dstore" u16
"fload" u16
"fstore" u16
"iinc" u16 i16
"iload" u16
"istore" u16
"lload" u16
"lstore" u16
"ret" u16
Constants:
utf:
WORD
STRING_LITERAL
utfref:
REF
utf
clsref:
REF
utf
single:
REF
utf
natref:
REF
utf utfref
mhnotref:
mhtag ref_or_tagged_const
mhtag:
"getField"
"getStatic"
"putField"
"putStatic"
"invokeVirtual"
"invokeStatic"
"invokeSpecial"
"newInvokeSpecial"
"invokeInterface"
tagged_const:
"Utf8" utf
"Int" i32
"Float" FLOAT_LITERAL
"Long" LONG_LITERAL
"Double" DOUBLE_LITERAL
"Class" utfref
"String" utfref
"MethodType" utfref
"Module" utfref
"Package" utfref
"Field" clsref natref
"Method" clsref natref
"InterfaceMethod" clsref natref
"NameAndType" utfref utfref
"MethodHandle" mhnotref
"Dynamic" bsref natref
"InvokeDynamic" bsref natref
ref_or_tagged_const:
REF
tagged_const
bs_args:
ref_or_tagged_const* ":"
bsref:
BSREF
mhnotref bs_args
ref_or_tagged_bootstrap:
BSREF
"Bootstrap" REF bs_args
"Bootstrap" mhnotref bs_args
ldc_rhs:
INTEGER_LITERAL
FLOAT_LITERAL
LONG_LITERAL
DOUBLE_LITERAL
STRING_LITERAL
REF
tagged_const