linux-kernel - Re: [RFC] Have insn decoder functions return success/failure

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Date:   Fri, 23 Oct 2020 11:17:55 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     x86-ml <x86@...nel.org>, Joerg Roedel <jroedel@...e.de>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] Have insn decoder functions return success/failure

On Thu, Oct 22, 2020 at 10:21:40PM +0900, Masami Hiramatsu wrote:
> extern void insn_init(struct insn *insn, const void *kaddr, int buf_len, int x86_64);
> extern void insn_get_prefixes(struct insn *insn);
> extern void insn_get_opcode(struct insn *insn);
> extern void insn_get_modrm(struct insn *insn);
> extern void insn_get_sib(struct insn *insn);
> extern void insn_get_displacement(struct insn *insn);
> extern void insn_get_immediate(struct insn *insn);
> extern void insn_get_length(struct insn *insn);

...

> Ah, so you meant that we don't need such a different insn_get_* APIs,
> but a single insn_decode() API, which will decode all fields.
> (IOW, alias of insn_init() and insn_get_length(), right?)

Yes, so there should be a balance between what one wants to decode:

length, opcodes, etc

vs

when one needs only a certain *single* aspect: sib, length,
displacement, etc.

So if you need a couple of things, you can simply call the insn_decode()
function - I'm reading forward and I like your naming :) - and when
that returns success, you can be sure that struct insn contains all the
fields needed.

Otherwise...

> > If there are specialized uses, you can call some of the insn_get_*
> > helpers if you're not interested in decoding the full insn.
> 
> OK, agreed.

... yes, exactly!

> > But if simply calling insn_decode_insn() would give you everything and
> > that is not that expensive, we can do that - API simplicity.
> 
> I rather like simple "insn_decode()" function, no need to repeat
> insn again.
> 
> int insn_decode(struct insn *insn, const void *kaddr, int buf_len, bool x86_64);

Yap, good.

Ok, seems we agree, lemme poke at this one more time, convert some users
and we can see how it looks like and talk then.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette