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

From: Anup Patel
Date: Mon Nov 26 2018 - 01:12:27 EST


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