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

[Jisheng Zhang <jszhang@kernel.org>]

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