Re: [PATCH v2] vmlinux.lds.h: Keep .ctors.* with .ctors - Fāng-ruì Sòng

From: "Fāng-ruì Sòng" <maskray@google.com>
To: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Arnd Bergmann <arnd@arndb.de>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	linux-arch <linux-arch@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>
Subject: Re: [PATCH v2] vmlinux.lds.h: Keep .ctors.* with .ctors
Date: Wed, 14 Oct 2020 21:53:39 -0700	[thread overview]
Message-ID: <CAFP8O3LvTkqUK3rp9Q17fmyN+xApZXA8Cs=MNvxrZ3SDCDRX3A@mail.gmail.com> (raw)
In-Reply-To: <202010141603.49EA0CE@keescook>

On Wed, Oct 14, 2020 at 4:04 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Sun, Oct 04, 2020 at 07:57:20PM -0700, Kees Cook wrote:
> > Under some circumstances, the compiler generates .ctors.* sections. This
> > is seen doing a cross compile of x86_64 from a powerpc64el host:
> >
> > x86_64-linux-gnu-ld: warning: orphan section `.ctors.65435' from `kernel/trace/trace_clock.o' being
> > placed in section `.ctors.65435'
> > x86_64-linux-gnu-ld: warning: orphan section `.ctors.65435' from `kernel/trace/ftrace.o' being
> > placed in section `.ctors.65435'
> > x86_64-linux-gnu-ld: warning: orphan section `.ctors.65435' from `kernel/trace/ring_buffer.o' being
> > placed in section `.ctors.65435'
> >
> > Include these orphans along with the regular .ctors section.
> >
> > Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
> > Tested-by: Stephen Rothwell <sfr@canb.auug.org.au>
> > Fixes: 83109d5d5fba ("x86/build: Warn on orphan section placement")
> > Signed-off-by: Kees Cook <keescook@chromium.org>
>
> Ping -- please take this for tip/urgent, otherwise we're drowning sfr in
> warnings. :)
>
> -Kees
>
> > ---
> > v2: brown paper bag version: fix whitespace for proper backslash alignment
> > ---
> >  include/asm-generic/vmlinux.lds.h | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> > index 5430febd34be..b83c00c63997 100644
> > --- a/include/asm-generic/vmlinux.lds.h
> > +++ b/include/asm-generic/vmlinux.lds.h
> > @@ -684,6 +684,7 @@
> >  #ifdef CONFIG_CONSTRUCTORS
> >  #define KERNEL_CTORS()       . = ALIGN(8);                      \
> >                       __ctors_start = .;                 \
> > +                     KEEP(*(SORT(.ctors.*)))            \
> >                       KEEP(*(.ctors))                    \
> >                       KEEP(*(SORT(.init_array.*)))       \
> >                       KEEP(*(.init_array))               \
> > --
> > 2.25.1
> >
>
> --
> Kees Cook
>
> --
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I think it would be great to figure out why these .ctors.* .dtors.*
are generated.
~GCC 4.7 switched to default to .init_array/.fini_array if libc
supports it. I have some refactoring in this area of Clang as well
(e.g. https://reviews.llvm.org/D71393)

And I am not sure SORT(.init_array.*) or SORT(.ctors.*) will work. The
correct construct is SORT_BY_INIT_PRIORITY(.init_array.*)