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

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Date:   Mon, 17 Dec 2018 14:59:19 +0200
From:   Nick Kossifidis <mick@....forth.gr>
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@...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

Στις 2018-12-17 11:36, Anup Patel έγραψε:
> 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
> 

Just a note on coding style, you should be using a macro instead of 0x10 
so that those who read the code can understand what it is and also a few 
comments since searching through the commit logs to understand why you 
used it isn't optimal.

Regards,
Nick