Jul 14, 2013 · Opcode: Opcode is short for operation code. As its name suggests, the opcode is a type of code that tells the machine what to do, i.e. what operation to perform. Opcode is a type of machine language instruction. Bytecode: Bytecode is similar to opcode in nature, as it also tells the machine what to do.

Feb 22, 2013 · The opcode determines if the operand is a signed value. All words, doublewords and quadwords are given with the low-order byte first. • +rb, +rw, +rd, +ro — Indicates the lower 3 bits of the opcode byte is used to encode the register operand without a modR/M byte. The instruction lists the corresponding hexadecimal value of the opcode byte ...

Jun 19, 2011 · While Intel Software Developer's Manual itself is definitely not very convenient to search through, the opcode tables in this manual could help. Take a look at the Appendix A "Opcode Map" in the volume 2A, 2B, 2C, and 2D of the manual, it might be useful:

The question is mostly related to PHP because IMHO opcode is mostly mentioned in PHP context. In fact Java is more popular for its byte-/opcode. 1) Is opcode just a portion of machine code, does machine code consist of opcodes? Yes, but this opcodes are machine-dependent.

Bit #1 is sometimes called the "direction" bit of the opcode. (Not to be confused with DF in EFLAGS, the direction flag). Also note that byte vs. word/dword/qword operand-size versions of those instructions differ only in the low bit, like 30 XOR r/m8, r8 vs. 31 XOR r/m16, r16. Again, this pattern shows up in the ALU instruction encodings that ...

Nov 11, 2010 · opcode_targets maps the instruction in the language's bytecode to the location in memory of the opcode implementation. This is faster because the processor's branch predictor can make a different prediction for each bytecode, in contrast to a switch statement that has only one branch instruction.

Jan 18, 2018 · li stands for Load Immediate and is a convenient way of loading an immediate up to 32 bits in size. Instructions like addi and ori can only encode 16-bit immediates, so the assembler may translate li into multiple instructions.

Aug 27, 2013 · I tried to use opcode from .text main(), this gave me segmentation fault, then .text main() + additionally .text _start(), with same result. So, what to choose from above sections, or how to generate only as minimized "prog" as with three sections?

Apr 24, 2015 · Have a look at this question: what does opcode FF350E204000 do? It explains that an entire group of instructions starts with FF: INC , DEC , CALLN , CALLF , JMPN , JMPF , PUSH . The instruction is determined by looking at bits 5 through 3 of the ModR/M byte (see e.g. here if you want to avoid the official intel manual), that is in your case ...

Oct 21, 2018 · Chrome failing to connect to websocket server (Opcode -1) "handshake was canceled" 15 What does the 'X-DevTools-Emulate-Network-Conditions-Client-Id' header key represent?