[PATCH v2 0/4] riscv: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION

Jisheng Zhang
2023-05-23T17:06:28Z

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(-)

--
2.40.1