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

[Palmer Dabbelt]

On Wed, 14 Jun 2023 09:25:49 PDT (-0700), jszhang@xxxxxxxxxx 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@xxxxxxxxxx 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