linux-kernel - Re: [PATCH] powerpc/build: vdso linker warning for orphan sections

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Message-ID: <87v8efu8rp.fsf@jogness.linutronix.de>
Date:   Wed, 19 Jul 2023 19:16:50 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/build: vdso linker warning for orphan sections

Hi Michael,

On 2023-07-19, Michael Ellerman <mpe@...erman.id.au> wrote:
> I regularly test with a gcc 5.5.0 / ld 2.29 toolchain and gcc 13.1.1 /
> ld 2.39, and I haven't seen the warning. I tried a bunch of others and
> can't reproduce it.

I will send my config in a separate email (without the lists in
CC). Building the vdso_prepare target is all that is needed.

> Can you confirm that this makes the warning go away?
>
> diff --git a/arch/powerpc/kernel/vdso/vdso64.lds.S b/arch/powerpc/kernel/vdso/vdso64.lds.S
> index bda6c8cdd459..286e1597c548 100644
> --- a/arch/powerpc/kernel/vdso/vdso64.lds.S
> +++ b/arch/powerpc/kernel/vdso/vdso64.lds.S
> @@ -85,7 +85,7 @@ SECTIONS
>  		*(.branch_lt)
>  		*(.data .data.* .gnu.linkonce.d.* .sdata*)
>  		*(.bss .sbss .dynbss .dynsbss)
> -		*(.opd)
> +		*(.opd .rela.opd)
>  		*(.glink .iplt .plt .rela*)

Hmmm. Not sure what that would change. And indeed it does not make the
warning go away.

Doing some testing it seems that previously .rela.opd was being silently
placed in the .rela.dyn section. So doing that explicitly obviously gets
rid of the warning:

Index: linux-6.5-rc2/arch/powerpc/kernel/vdso/vdso64.lds.S
===================================================================
--- linux-6.5-rc2.orig/arch/powerpc/kernel/vdso/vdso64.lds.S
+++ linux-6.5-rc2/arch/powerpc/kernel/vdso/vdso64.lds.S
@@ -69,7 +69,7 @@ SECTIONS
 	.eh_frame_hdr	: { *(.eh_frame_hdr) }		:text	:eh_frame_hdr
 	.eh_frame	: { KEEP (*(.eh_frame)) }	:text
 	.gcc_except_table : { *(.gcc_except_table) }
-	.rela.dyn ALIGN(8) : { *(.rela.dyn) }
+	.rela.dyn ALIGN(8) : { *(.rela.dyn) *(.rela.opd) }
 
 	.got ALIGN(8)	: { *(.got .toc) }

But if the goal is to get rid of .rela.opd then the question is: why is
the linker complaining about it being discarded?

John