Re: [PATCH v2 0/4] riscv: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION

Palmer Dabbelt
2023-06-15T13:54:44Z

On Wed, 14 Jun 2023 09:25:49 PDT (-0700), jszhang@kernel.org wrote:
>
> On Wed, Jun 14, 2023 at 07:49:17AM -0700, Palmer Dabbelt wrote:
>> On Tue, 23 May 2023 09:54:58 PDT (-0700), jszhang@kernel.org wrote:
>> > When trying to run linux with various opensource riscv core on
>> > resource limited FPGA platforms, for example, those FPGAs with less
>> > than 16MB SDRAM, I want to save mem as much as possible. One of the
>> > major technologies is kernel size optimizations, I found that riscv
>> > does not currently support HAVE_LD_DEAD_CODE_DATA_ELIMINATION, which
>> > passes -fdata-sections, -ffunction-sections to CFLAGS and passes the
>> > --gc-sections flag to the linker.
>> >
>> > This not only benefits my case on FPGA but also benefits defconfigs.
>> > Here are some notable improvements from enabling this with defconfigs:
>> >
>> > nommu_k210_defconfig:
>> > text data bss dec hex
>> > 1112009 410288 59837 1582134 182436 before
>> > 962838 376656 51285 1390779 1538bb after
>> >
>> > rv32_defconfig:
>> > text data bss dec hex
>> > 8804455 2816544 290577 11911576 b5c198 before
>> > 8692295 2779872 288977 11761144 b375f8 after
>> >
>> > defconfig:
>> > text data bss dec hex
>> > 9438267 3391332 485333 13314932 cb2b74 before
>> > 9285914 3350052 483349 13119315 c82f53 after
>> >
>> > patch1 and patch2 are clean ups.
>> > patch3 fixes a typo.
>> > patch4 finally enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION for riscv.
>> >
>> > NOTE: Zhangjin Wu firstly sent out a patch to enable dead code
>> > elimination for riscv several months ago, I didn't notice it until
>> > yesterday. Although it missed some preparations and some sections's
>> > keeping, he is the first person to enable this feature for riscv. To
>> > ease merging, this series take his patch into my entire series and
>> > makes patch4 authored by him after getting his ack to reflect
>> > the above fact.
>> >
>> > Since v1:
>> > - collect Reviewed-by, Tested-by tag
>> > - Make patch4 authored by Zhangjin Wu, add my co-developed-by tag
>> >
>> > Jisheng Zhang (3):
>> > riscv: move options to keep entries sorted
>> > riscv: vmlinux-xip.lds.S: remove .alternative section
>> > vmlinux.lds.h: use correct .init.data.* section name
>> >
>> > Zhangjin Wu (1):
>> > riscv: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION
>> >
>> > arch/riscv/Kconfig | 13 +-
>> > arch/riscv/kernel/vmlinux-xip.lds.S | 6 -
>> > arch/riscv/kernel/vmlinux.lds.S | 6 +-
>> > include/asm-generic/vmlinux.lds.h | 2 +-
>> > 4 files changed, 11 insertions(+), 16 deletions(-)
>>
>> Do you have a base commit for this? It's not applying to 6.4-rc1 and the
>> patchwork bot couldn't find one either.
>
> Hi Palmer,
>
> Commit 3b90b09af5be ("riscv: Fix orphan section warnings caused by
> kernel/pi") touches vmlinux.lds.S, so to make the merge easy, this
> series is based on 6.4-rc2.

Thanks.

>
> Thanks