code <- r"(
LDCONST 1
LDCONST 2
ADD
RETURN
)"
bc <- asm(code)
bc<bytecode: 0x13c77be80>eval(bc)[1] 34 Assembling bytecode
After exploring the disassembly process (Section 3), it is possible to take the output and re-compile it into an executable bytecode object.
Compiling bytecode assembly to an R bytecode object is achieved using rbytecode::asm().
It is also possible to compile bytecode in two steps using parse_code() to produce a bcdf, and then compile the bcdf data.frame to a bytecode object using compile_bcdf().
4.1 Compiling bytecode - simple example
asm() accepts a single string of bytecode instructions (one instruction per line).
The input is parsed and compiled into bytecode using (internal) parts of base R’s {compiler} package.
4.2 Compiling bytecode - two-step process
code <- r"(
LDCONST 1
LDCONST 2
ADD
RETURN
)"
bcdf <- parse_code(code)
bcdf line depth pc opcode op args expr
1 2 0 1 16 LDCONST 1 NULL
2 3 0 3 16 LDCONST 2 NULL
3 4 0 5 44 ADD NULL NULL
4 5 0 7 1 RETURN NULL NULLbc <- compile_bcdf(bcdf)
bc<bytecode: 0x13ccbdde8>eval(bc)[1] 3