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assembly is just mnemonics for the machine code - that is very important to remember. its a different encoding, but its one which has a strong and tightly coupl

by jheriko 13y ago

assembly is just mnemonics for the machine code - that is very important to remember. its a different encoding, but its one which has a strong and tightly coupled relationship to the point where disassemblers are a thing.. sure asm.js is encoded as text, but its not encoding anything close to what assembly languages do.

acjohnson55 13y ago
I have another reply to that effect somewhere in this thread :) Modern assembly languages often at a slightly higher level of representation than 1-to-1 with the instruction set so it's tough to draw a tough line, but yes, generally speaking, you should be able to translate the majority of the language to machine code with opcode tables. It's also interesting that machine code isn't even the lowest level representation of machine instructions on many architectures, which internally use microcode to implement architectural instructions. My point was that LLVM bitcode and asm.js are both intermediate targets, but not exactly the same.
- jheriko 13y ago
  You mean macro assembler languages? Its a pedantic distinction but I wasn't intending to imply those... 'Pure' assembly languages are still not 1 to 1 but are never worse than many to one, eg nop is often a real, but useless instruction with some other mnemonic.... Not sure what you point is about microcode... That is an implementation detail which, even for eg, x86 LEA where you think you are leveraging it, it is not important or useful beyond trying to understand performance characteristics. What you get to work with is whole instructions.
  - acjohnson55 13y ago
    We agree! I'm not arguing with you. I'm just trying to provide a bit more context for people who are trying to understand the purpose of all this. Judging by the vast majority of remarks on the article, there's a lot of misunderstanding of how this stuff works.

by jheriko 13y ago

acjohnson55 13y ago

I have another reply to that effect somewhere in this thread :) Modern assembly languages often at a slightly higher level of representation than 1-to-1 with the instruction set so it's tough to draw a tough line, but yes, generally speaking, you should be able to translate the majority of the language to machine code with opcode tables. It's also interesting that machine code isn't even the lowest level representation of machine instructions on many architectures, which internally use microcode to implement architectural instructions. My point was that LLVM bitcode and asm.js are both intermediate targets, but not exactly the same.

jheriko 13y ago
You mean macro assembler languages? Its a pedantic distinction but I wasn't intending to imply those... 'Pure' assembly languages are still not 1 to 1 but are never worse than many to one, eg nop is often a real, but useless instruction with some other mnemonic.... Not sure what you point is about microcode... That is an implementation detail which, even for eg, x86 LEA where you think you are leveraging it, it is not important or useful beyond trying to understand performance characteristics. What you get to work with is whole instructions.
- acjohnson55 13y ago
  We agree! I'm not arguing with you. I'm just trying to provide a bit more context for people who are trying to understand the purpose of all this. Judging by the vast majority of remarks on the article, there's a lot of misunderstanding of how this stuff works.