| Message ID | 20181219123657.61270-1-anup@brainfault.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] RISC-V: Make BSS section as the last section in vmlinux.lds.S | expand |
On Wed, Dec 19, 2018 at 8:37 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. In summary, this patch reduces > Linux-4.20-rc4 flat kernel Image size by 809 KB. > > Signed-off-by: Anup Patel <anup@brainfault.org> > --- > > Changes since v1: > - Introduce MAX_BYTES_PER_LONG define and use it in-place of > 0x10 magic value > > arch/riscv/kernel/vmlinux.lds.S | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S index 65df1dfdc303..1e1395d63dab 100644 --- a/arch/riscv/kernel/vmlinux.lds.S +++ b/arch/riscv/kernel/vmlinux.lds.S @@ -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
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> --- Changes since v1: - Introduce MAX_BYTES_PER_LONG define and use it in-place of 0x10 magic value arch/riscv/kernel/vmlinux.lds.S | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)