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 <[email protected]>
---
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
On Mon, Nov 26, 2018 at 2:12 PM Anup Patel <[email protected]> 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 <[email protected]>
> ---
> arch/riscv/kernel/vmlinux.lds.S | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
Reviewed-by: Bin Meng <[email protected]>
Tested-by: Bin Meng <[email protected]>
On Mon, Nov 26, 2018 at 11:42 AM Anup Patel <[email protected]> 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 <[email protected]>
> ---
> 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
Στις 2018-12-17 11:36, Anup Patel έγραψε:
> On Mon, Nov 26, 2018 at 11:42 AM Anup Patel <[email protected]>
> 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 <[email protected]>
>> ---
>> 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
On Mon, Dec 17, 2018 at 6:29 PM Nick Kossifidis <[email protected]> wrote:
>
> Στις 2018-12-17 11:36, Anup Patel έγραψε:
> > On Mon, Nov 26, 2018 at 11:42 AM Anup Patel <[email protected]>
> > 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 <[email protected]>
> >> ---
> >> 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.
RISC-V can support 32bit, 64bit and 128bit machine-word sizes.
The 0x10 number is the machine-word size in bytes for 128bit
RISC-V CPU (i.e. maximum machine-word size).
I will add a macro MAX_BYTES_PER_LONG in vmlinux.lds.S and
use it in-place of 0x10
Regards,
Anup
On Mon, 17 Dec 2018 01:36:45 PST (-0800), [email protected] wrote:
> On Mon, Nov 26, 2018 at 11:42 AM Anup Patel <[email protected]> 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 <[email protected]>
>> ---
>> 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?
Sorry, I haven't had a chance to look at it yet. Aside from the macro issue
mentioned by Nick it seems OK.
On Fri, Dec 21, 2018 at 2:10 AM Palmer Dabbelt <[email protected]> wrote:
>
> On Mon, 17 Dec 2018 01:36:45 PST (-0800), [email protected] wrote:
> > On Mon, Nov 26, 2018 at 11:42 AM Anup Patel <[email protected]> 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 <[email protected]>
> >> ---
> >> 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?
>
> Sorry, I haven't had a chance to look at it yet. Aside from the macro issue
> mentioned by Nick it seems OK.
I have send v2 to address Nick's comment.
Regards,
Anup