[PATCH 0/4] riscv: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION

Jisheng Zhang
2023-05-11T14:40:27Z

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.

Jisheng Zhang (4):
riscv: vmlinux-xip.lds.S: remove .alternative section
riscv: move HAVE_RETHOOK to keep entries sorted
riscv: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION
vmlinux.lds.h: use correct .init.data.* section name

arch/riscv/Kconfig | 3 ++-
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, 6 insertions(+), 11 deletions(-)

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2.40.1