From: Liuyuntao (F) <liuyuntao12@xxxxxxxxxx> Date: Thu, 25 Apr 2024 14:37:19 +0800 > > > On 2024/4/24 19:06, Alexander Lobakin wrote: >> 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 > > I apply your patch, and use LLVM toolchain to compile the kernel, it not > boot on QEMU. > I use the following command. >> qemu-system-x86_64 -smp 2 -m 1024M -nographic -kernel >> mainline_linux/arch/x86/boot/bzImage -hda rootfs.img -append >> "root=/dev/sda console=ttyS0 rootfstype=ext4 init=/linuxrc rw" > Have you tested your patch on the latest mainline version? Nope, it was a year ago and I haven't touched it since then. Did the low-level code change a lot? > Thanks. > Yuntao. Thanks, Olek
