On Mon, Apr 22, 2024 at 3:41 PM Yuntao Liu <liuyuntao12@xxxxxxxxxx> wrote: > > 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. > > 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. > --- > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh > index 7862a8101747..7287b5a9f17d 100755 > --- a/scripts/link-vmlinux.sh > +++ b/scripts/link-vmlinux.sh > @@ -60,7 +60,7 @@ vmlinux_link() > # skip output file argument > shift > > - if is_enabled CONFIG_LTO_CLANG || is_enabled CONFIG_X86_KERNEL_IBT; then > + if [ is_enabled CONFIG_LTO_CLANG || is_enabled CONFIG_X86_KERNEL_IBT ] && [ ! is_enabled CONFIG_LD_DEAD_CODE_DATA_ELIMINATION ]; then > # Use vmlinux.o instead of performing the slow LTO link again. > objs=vmlinux.o > libs= > -- This is wrong. You should not put is_enabled inside [ ... ] (is_enabled CONFIG_LTO_CLANG || is_enabled CONFIG_X86_KERNEL_IBT) && ! is_enabled CONFIG_LD_DEAD_CODE_DATA_ELIMINATION is still weird. When CONFIG_LTO_CLANG=y and CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y, the result of LTO will be discarded. -- Best Regards Masahiro Yamada
