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

[Nick Kossifidis]

ÎÏÎÏ 2018-12-17 11:36, Anup Patel ÎÎÏÎÏÎ:
> On Mon, Nov 26, 2018 at 11:42 AM Anup Patel <anup@xxxxxxxxxxxxxx> 
> 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@xxxxxxxxxxxxxx>
> > ---
> >  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