linux-kernel - Re: [PATCH] powerpc: Handle .text.{hot,unlikely}.* in linker script

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Date:   Mon, 4 Jan 2021 21:55:20 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] powerpc: Handle .text.{hot,unlikely}.* in linker script

On Mon, Jan 4, 2021 at 9:49 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> Commit eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input
> sections") added ".text.unlikely.*" and ".text.hot.*" due to an LLVM
> change [1].
>
> After another LLVM change [2], these sections are seen in some PowerPC
> builds, where there is a orphan section warning then build failure:
>

Looks like you forgot to add your references/links to [1] and [2].

Might be good to mention...?

With CONFIG_LD_ORPHAN_WARN=y is enabled

- Sedat

> $ make -skj"$(nproc)" \
>        ARCH=powerpc CROSS_COMPILE=powerpc64le-linux-gnu- LLVM=1 O=out \
>        distclean powernv_defconfig zImage.epapr
> ld.lld: warning: kernel/built-in.a(panic.o):(.text.unlikely.) is being placed in '.text.unlikely.'
> ...
> ld.lld: warning: address (0xc000000000009314) of section .text is not a multiple of alignment (256)
> ...
> ERROR: start_text address is c000000000009400, should be c000000000008000
> ERROR: try to enable LD_HEAD_STUB_CATCH config option
> ERROR: see comments in arch/powerpc/tools/head_check.sh
> ...
>
> Explicitly handle these sections like in the main linker script so
> there is no more build failure.
>
> Cc: stable@...r.kernel.org
> Fixes: 83a092cf95f2 ("powerpc: Link warning for orphan sections")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1218
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  arch/powerpc/kernel/vmlinux.lds.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
> index 0318ba436f34..8e0b1298bf19 100644
> --- a/arch/powerpc/kernel/vmlinux.lds.S
> +++ b/arch/powerpc/kernel/vmlinux.lds.S
> @@ -85,7 +85,7 @@ SECTIONS
>                 ALIGN_FUNCTION();
>  #endif
>                 /* careful! __ftr_alt_* sections need to be close to .text */
> -               *(.text.hot TEXT_MAIN .text.fixup .text.unlikely .fixup __ftr_alt_* .ref.text);
> +               *(.text.hot .text.hot.* TEXT_MAIN .text.fixup .text.unlikely .text.unlikely.* .fixup __ftr_alt_* .ref.text);
>  #ifdef CONFIG_PPC64
>                 *(.tramp.ftrace.text);
>  #endif
>
> base-commit: d8a4f20584d5906093a8fc6aa06622102a501095
> --
> 2.30.0
>
> --
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