linux-kernel - Re: [PATCH 21/29] objtool: Rename --duplicate to --lto

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Message-ID: <20220228200934.GF11184@worktop.programming.kicks-ass.net>
Date:   Mon, 28 Feb 2022 21:09:34 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com
Subject: Re: [PATCH 21/29] objtool: Rename --duplicate to --lto

On Mon, Feb 28, 2022 at 10:32:28AM -0800, Josh Poimboeuf wrote:

> Thanks for the explanations.  To summarize, we have:
> 
>   A) legacy mode:
> 
>      translation unit: objtool check [--module]
>      vmlinux.o:        N/A
>      module:           N/A
> 
>   B) CONFIG_VMLINUX_VALIDATION=y && !(CONFIG_X86_KERNEL_IBT=y || CONFIG_LTO=y)
> 
>      translation unit: objtool check [--module]
>      vmlinux:          objtool check --vmlinux --noinstr
>      module:           objtool check --module --noinstr

Not the module thing here; noinstr never leaves the core kernel (for
now; I need me a few compiler features before I can tackle the idle path
issues).

>   C) CONFIG_X86_KERNEL_IBT=y || CONFIG_LTO=y:
> 
>      translation unit: N/A
>      vmlinux:          objtool check --vmlinux --noinstr --lto
>      module:           objtool check --module --noinstr --lto
> 
> Right?

More or less, with the one caveat above.

> I think I get it, but it's mental gymnastics for me to remember how the
> options interact.  It still seems counterintuitive, because whatever
> "objtool check" does to a translation unit, I'd expect "objtool check
> --vmlinux" to do the same things.

I think I agree. It is a bit weird.

> So how about we just get rid of the magical --vmlinux and --lto options
> altogether, and make --noinstr additive, like all the other options?
>
>   A) legacy mode:
>      .o files: objtool check [--module]
>       vmlinux: N/A
>        module: N/A
>
>   B) CONFIG_NOINSTR_VALIDATION=y && !(CONFIG_X86_KERNEL_IBT=y || CONFIG_LTO=y):
>      .o files: objtool check [--module]
>       vmlinux: objtool check --noinstr-only
>        module: objtool check --module --noinstr-only
>
>   C) CONFIG_X86_KERNEL_IBT=y || CONFIG_LTO=y:
>      .o files: N/A
>       vmlinux: objtool check --noinstr
>        module: objtool check --module --noinstr

I like the --noinstr-only thing. But I think I still like a flag to
differentiate between TU/.o file and vmlinux/whole-module invocation.

Anyway, you ok with me cleaning this up later, in a separate series?