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

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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. In summary, this patch reduces
Linux-4.20-rc4 flat kernel Image size by 809 KB.

Signed-off-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
This commit is contained in:
Anup Patel 2018-12-19 18:06:57 +05:30 committed by Palmer Dabbelt
parent bfeffd1552
commit 22e6a2e14c
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1 changed files with 6 additions and 2 deletions
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8
arch/riscv/kernel/vmlinux.lds.S
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@ -18,6 +18,8 @@
#include <asm/cache.h>
#include <asm/thread_info.h>
#define MAX_BYTES_PER_LONG 0x10
OUTPUT_ARCH(riscv)
ENTRY(_start)
@ -74,8 +76,6 @@ SECTIONS
*(.sbss*)
}
BSS_SECTION(PAGE_SIZE, PAGE_SIZE, 0)
EXCEPTION_TABLE(0x10)
NOTES
@ -83,6 +83,10 @@ SECTIONS
*(.rel.dyn*)
}
BSS_SECTION(MAX_BYTES_PER_LONG,
MAX_BYTES_PER_LONG,
MAX_BYTES_PER_LONG)
_end = .;
STABS_DEBUG