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

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Date:   Sun, 23 Dec 2018 20:28:21 +0530
From:   Anup Patel <anup@...infault.org>
To:     Palmer Dabbelt <palmer@...ive.com>
Cc:     Albert Ou <aou@...s.berkeley.edu>,
        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 Fri, Dec 21, 2018 at 2:10 AM Palmer Dabbelt <palmer@...ive.com> wrote:
>
> On Mon, 17 Dec 2018 01:36:45 PST (-0800), anup@...infault.org wrote:
> > 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?
>
> Sorry, I haven't had a chance to look at it yet.  Aside from the macro issue
> mentioned by Nick it seems OK.

I have send v2 to address Nick's comment.

Regards,
Anup