linux-kernel - Re: [PATCH] RISC-V: Make BSS section as the last section in vmlinux.lds.S

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Message-ID: <CAAhSdy1danjgviJ2WGGEANQXFkzZzXUdCj+04dZ4eLjcVOt14A@mail.gmail.com>
Date:   Mon, 17 Dec 2018 15:06:45 +0530
From:   Anup Patel <anup@...infault.org>
To:     Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>
Cc:     Atish Patra <atish.patra@....com>,
        Christoph Hellwig <hch@...radead.org>,
        linux-riscv@...ts.infradead.org,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] RISC-V: Make BSS section as the last section in vmlinux.lds.S

On Mon, Nov 26, 2018 at 11:42 AM Anup Patel <anup@...infault.org> wrote:
>
> The objcopy only emits loadable sections when creating flat kernel
> Image. To have minimal possible size of flat kernel Image, we should
> have all non-loadable sections after loadable sections.
>
> Currently, execption table section (loadable section) is after BSS
> section (non-loadable section) in the RISC-V vmlinux.lds.S. This
> is not optimal for having minimal flat kernel Image size hence this
> patch makes BSS section as the last section in RISC-V vmlinux.lds.S.
>
> In addition, we make BSS section aligned to 16byte instead of PAGE
> aligned which further reduces flat kernel Image size by few KBs.
>
> The flat kernel Image size of Linux-4.20-rc4 using GCC 8.2.0 is
> 8819980 bytes with current RISC-V vmlinux.lds.S and it reduces to
> 7991740 bytes with this patch applied using GCC 8.2.0. In summary,
> this patch reduces Linux-4.20-rc4 flat kernel Image size by 809 KB.
>
> Signed-off-by: Anup Patel <anup@...infault.org>
> ---
>  arch/riscv/kernel/vmlinux.lds.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> index 65df1dfdc303..cc99eed44931 100644
> --- a/arch/riscv/kernel/vmlinux.lds.S
> +++ b/arch/riscv/kernel/vmlinux.lds.S
> @@ -74,8 +74,6 @@ SECTIONS
>                 *(.sbss*)
>         }
>
> -       BSS_SECTION(PAGE_SIZE, PAGE_SIZE, 0)
> -
>         EXCEPTION_TABLE(0x10)
>         NOTES
>
> @@ -83,6 +81,8 @@ SECTIONS
>                 *(.rel.dyn*)
>         }
>
> +       BSS_SECTION(0x10, 0x10, 0x10)
> +
>         _end = .;
>
>         STABS_DEBUG
> --
> 2.17.1
>

Hi All,

Any comment on this patch?

Regards,
Anup