[0/4] riscv: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION

Message

Jisheng Zhang May 11, 2023, 2:12 p.m. UTC

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(-)