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* [PATCH] RISC-V: Make BSS section as the last section in vmlinux.lds.S
@ 2018-11-26  6:08 anup
  2018-11-26  6:08 ` Anup Patel
  2018-11-29  7:36 ` bmeng.cn
  0 siblings, 2 replies; 4+ messages in thread
From: anup @ 2018-11-26  6:08 UTC (permalink / raw)
  To: linux-riscv

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@brainfault.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

^ permalink raw reply	[flat|nested] 4+ messages in thread

* [PATCH] RISC-V: Make BSS section as the last section in vmlinux.lds.S
  2018-11-26  6:08 [PATCH] RISC-V: Make BSS section as the last section in vmlinux.lds.S anup
@ 2018-11-26  6:08 ` Anup Patel
  2018-11-29  7:36 ` bmeng.cn
  1 sibling, 0 replies; 4+ messages in thread
From: Anup Patel @ 2018-11-26  6:08 UTC (permalink / raw)
  To: Palmer Dabbelt, Albert Ou
  Cc: Christoph Hellwig, Atish Patra, linux-riscv, linux-kernel, Anup Patel

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@brainfault.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


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linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

^ permalink raw reply	[flat|nested] 4+ messages in thread

* [PATCH] RISC-V: Make BSS section as the last section in vmlinux.lds.S
  2018-11-26  6:08 [PATCH] RISC-V: Make BSS section as the last section in vmlinux.lds.S anup
  2018-11-26  6:08 ` Anup Patel
@ 2018-11-29  7:36 ` bmeng.cn
  2018-11-29  7:36   ` Bin Meng
  1 sibling, 1 reply; 4+ messages in thread
From: bmeng.cn @ 2018-11-29  7:36 UTC (permalink / raw)
  To: linux-riscv

On Mon, Nov 26, 2018 at 2:12 PM Anup Patel <anup@brainfault.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@brainfault.org>
> ---
>  arch/riscv/kernel/vmlinux.lds.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>

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

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] RISC-V: Make BSS section as the last section in vmlinux.lds.S
  2018-11-29  7:36 ` bmeng.cn
@ 2018-11-29  7:36   ` Bin Meng
  0 siblings, 0 replies; 4+ messages in thread
From: Bin Meng @ 2018-11-29  7:36 UTC (permalink / raw)
  To: Anup Patel; +Cc: aou, palmer, linux-kernel, hch, atish.patra, linux-riscv

On Mon, Nov 26, 2018 at 2:12 PM Anup Patel <anup@brainfault.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@brainfault.org>
> ---
>  arch/riscv/kernel/vmlinux.lds.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>

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

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

^ permalink raw reply	[flat|nested] 4+ messages in thread

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Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-11-26  6:08 [PATCH] RISC-V: Make BSS section as the last section in vmlinux.lds.S anup
2018-11-26  6:08 ` Anup Patel
2018-11-29  7:36 ` bmeng.cn
2018-11-29  7:36   ` Bin Meng

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