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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Fri, 27 May 2022 15:04:57 +0900
Message-ID: <CAK7LNATeHZK+qv9e375fsZwtiuUE_MrfBA9Rhzz3uY8tF4EXUg@mail.gmail.com>
Subject: Re: linux-next: manual merge of the tip tree with the kbuild tree
To:     Josh Poimboeuf <jpoimboe@kernel.org>
Cc:     Stephen Rothwell <sfr@canb.auug.org.au>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Next Mailing List <linux-next@vger.kernel.org>
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On Fri, May 27, 2022 at 1:47 PM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> On Fri, May 27, 2022 at 11:19:02AM +0900, Masahiro Yamada wrote:
> > [1] original behavior in Josh's commit
> >
> > $ git checkout 753da4179d08b625d8df72e97724e22749969fd3
> > $ make defconfig
> > $ make -j8 kernel/
> > $ head -n 1   kernel/.fork.o.cmd
> >
> >
> > I do not see the "--linked" parameter in the objtool command.
> >
> >
> >
> >
> > [2] behavior in linux-next
> >
> >
> > $ git checkout next-20220523
> > $ make defconfig
> > $ make -j8 kernel/
> > $ head -n 1   kernel/.fork.o.cmd
> >
> > I see the "--linked" parameter in the objtool command.
> >
> > kernel/fork.o  is a direct output from GCC,
> > not from linker.
>
> Yes, good catch.  That flag should only be used for linked objects like
> vmlinux.o or some_module.o.
>
> Objtool only runs on such objects when CONFIG_LTO_CLANG,
> CONFIG_X86_KERNEL_IBT, or CONFIG_NOINSTR_VALIDATION (vmlinux.o-only) is
> enabled.
>
> --
> Josh


When CONFIG_LTO_CLANG=y or CONFIG_X86_KERNEL_IBT=y
is "--linked" necessary for single-object modules?


"single-object module" means a module that consists of only one object.

See this figure:
https://patchwork.kernel.org/project/linux-kbuild/patch/20220513113930.10488-6-masahiroy@kernel.org/


In your commit, --linked is passed to all *.prelink.o
whether it consists of a single object or links
multiple objects.


-- 
Best Regards
Masahiro Yamada