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c828856b51
Select CONFIG_HAVE_LD_DEAD_CODE_DATA_ELIMINATION for RISC-V, allowing
the user to enable dead code elimination. In order for this to work,
ensure that we keep the alternative table by annotating them with KEEP.
This boots well on qemu with both rv32_defconfig & rv64 defconfig, but
it only shrinks their builds by ~1%, a smaller config is thereforce
customized to test this feature:
| rv32 | rv64
--------|------------------------|---------------------
No DCE | 4460684 | 4893488
DCE | 3986716 | 4376400
Shrink | 473968 (~10.6%) | 517088 (~10.5%)
The config used above only reserves necessary options to boot on qemu
with serial console, more like the size-critical embedded scenes:
- rv64 config: https://pastebin.com/crz82T0s
- rv32 config: rv64 config + 32-bit.config
Here is Jisheng's original commit-msg:
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
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| .. | ||
| boot | ||
| configs | ||
| errata | ||
| include | ||
| kernel | ||
| kvm | ||
| lib | ||
| mm | ||
| net | ||
| purgatory | ||
| tools | ||
| Kbuild | ||
| Kconfig | ||
| Kconfig.debug | ||
| Kconfig.errata | ||
| Kconfig.socs | ||
| Makefile | ||
| Makefile.postlink | ||