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

Palmer Dabbelt
2023-06-19T22:06:46Z

On Thu, 15 Jun 2023 06:54:33 PDT (-0700), Palmer Dabbelt wrote:
> 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.

Sorry to be so slow here, but I think this is causing LLD to hang on
allmodconfig. I'm still getting to the bottom of it, there's a few
other things I have in flight still.

>
>>
>> Thanks