From: Yuntao Liu <liuyuntao12@xxxxxxxxxx> Date: Mon, 22 Apr 2024 06:05:56 +0000 > The current x86 architecture does not yet support the > HAVE_LD_DEAD_CODE_DATA_ELIMINATION feature. x86 is widely used in > embedded scenarios, and enabling this feature would be beneficial for > reducing the size of the kernel image. > > In order to make this work, we keep the necessary tables by annotating > them with KEEP, also it requires further changes to linker script to KEEP > some tables and wildcard compiler generated sections into the right place. > > Enabling CONFIG_UNWINDER_ORC or CONFIG_MITIGATION_RETPOLINE will enable > the objtool's --orc and --retpoline parameters, which will alter the > layout of the binary file, thereby preventing gc-sections from functioning > properly. Therefore, HAVE_LD_DEAD_CODE_DATA_ELIMINATION should only be > selected when they are not enabled. Dunno, I have DCE enabled for years on my home kernel, see commit [0] with both ORC and retpolines enabled, and I didn't have any issues. vmlinux still shrinks well, even with Clang LTO. > > Enabling CONFIG_LTO_CLANG or CONFIG_X86_KERNEL_IBT will use vmlinux.o > instead of performing the slow LTO link again. This can also prevent > gc-sections from functioning properly. Therefore, using this optimization > when CONFIG_LD_DEAD_CODE_DATA_ELIMINATION is not enabled. > > The size comparison of zImage is as follows: > x86_def_defconfig i386_defconfig tinyconfig > 10892288 10826240 607232 no dce > 10748928 10719744 529408 dce > 1.3% 0.98% 12.8% shrink > > When using smaller config file, there is a significant reduction in the > size of the zImage. [0] https://github.com/solbjorn/linux/commit/25c4953ea73d Thanks, Olek
