linux-kernel - Re: [PATCH v2] RISC-V: Make BSS section as the last section in vmlinux.lds.S

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Message-ID: <CAEUhbmXNmzHVnzj88T5jxDXs=Rx_kD9fgayZ4r3xvgAOYXKWjw@mail.gmail.com>
Date:   Thu, 20 Dec 2018 14:16:47 +0800
From:   Bin Meng <bmeng.cn@...il.com>
To:     Anup Patel <anup@...infault.org>
Cc:     Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christoph Hellwig <hch@...radead.org>,
        Atish Patra <atish.patra@....com>,
        linux-riscv@...ts.infradead.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] RISC-V: Make BSS section as the last section in vmlinux.lds.S

On Wed, Dec 19, 2018 at 8:37 PM 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. In summary, this patch reduces
> Linux-4.20-rc4 flat kernel Image size by 809 KB.
>
> Signed-off-by: Anup Patel <anup@...infault.org>
> ---
>
> Changes since v1:
>  - Introduce MAX_BYTES_PER_LONG define and use it in-place of
>    0x10 magic value
>
>  arch/riscv/kernel/vmlinux.lds.S | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>

Reviewed-by: Bin Meng <bmeng.cn@...il.com>