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Comment by Joker_vD | Hacker News Reader

Doesn't GCC inline assembly actually track that info, with the "clobber" section?

Yes, but it's not a property of the assembly (or assembler), it's a necessity for the compiler to correctly codegen around the inline assembly.

Historically, assemblers have been really dumb, so ABI is not a thing they'd track, especially as... I don't think they know what functions are? So while they can notice call/ret, they have no knowledge of a label being a jump or call target per-se, do they?

So you'd need an assembly-like language to encode this sort of information.

I mean if you have a macro assembler you should be able to write a macro that generates "save registers" instructions before a section of code and "restore registers" instructions after it. The assembler doesn't need to know our care that this section of code is a function.

It's interesting how blurry the line is between a good, full-featured assembler and a crappy compiler!

> I mean if you have a macro assembler you should be able to write a macro that generates "save registers" instructions before a section of code and "restore registers" instructions after it.

Except you want a "macro" which:

- saves only the registers you touched

- which are callee-saved

- according to the ABI you're targeting

And you really only want that for functions, because... that's where ABIs come into play.

> I don't think they know what functions are?

It's a long time since I tangled with x86 assembler; but as I recall, ENTER and LEAVE were specifically for functions, and I'm not aware of any other use for them.

ENTER and LEAVE were specific x86 instructions though, not some kind of assembler special sauce. The assembler just translated your ENTER instruction into the corresponding machine opcode; no ABI knowledge required whatsoever.

I think most assemblers know what functions are. There are usually directives to indicate this. They help with emitting symbols (you need the function name to be emitted or no-one can call it), stack unwind information, and other information (some of which may also be required by the ABI). Here's some relevant documentation for MASM https://learn.microsoft.com/en-us/cpp/assembler/masm/proc?vi...

The short version of it is that assemblers these days are rarely - if ever - just a zero-context stream of machine instructions. There is far more, some of it actually required.

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