Messages in this thread | | | Date | Sat, 9 Mar 2024 14:56:46 +0800 | Subject | Re: [PATCH-next v2] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION | From | "liuyuntao (F)" <> |
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On 2024/3/8 22:27, Ard Biesheuvel wrote: > On Fri, 8 Mar 2024 at 14:16, Arnd Bergmann <arnd@arndb.de> wrote: >> >> On Thu, Mar 7, 2024, at 16:12, Yuntao Liu wrote: >>> The current arm32 architecture does not yet support the >>> HAVE_LD_DEAD_CODE_DATA_ELIMINATION feature. arm32 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. >>> >>> It boots normally with defconfig, vexpress_defconfig and tinyconfig. >>> >>> The size comparison of zImage is as follows: >>> defconfig vexpress_defconfig tinyconfig >>> 5137712 5138024 424192 no dce >>> 5032560 4997824 298384 dce >>> 2.0% 2.7% 29.7% shrink >>> >>> When using smaller config file, there is a significant reduction in the >>> size of the zImage. >>> >>> We also tested this patch on a commercially available single-board >>> computer, and the comparison is as follows: >>> a15eb_config >>> 2161384 no dce >>> 2092240 dce >>> 3.2% shrink >>> >>> The zImage size has been reduced by approximately 3.2%, which is 70KB on >>> 2.1M. >>> >>> Signed-off-by: Yuntao Liu <liuyuntao12@huawei.com> >> >> I've retested with both gcc-13 and clang-18, and so no >> more build issues. Your previous version already worked >> fine for me. >> >> I did some tests combining this with CONFIG_TRIM_UNUSED_KSYMS, >> which showed a significant improvement as expected. I also >> tried combining it with an experimental CONFIG_LTO_CLANG >> patch, but that did not show any further improvements. >> >> Tested-by: Arnd Bergmann <arnd@arndb.de> >> Reviewed-by: Arnd Bergmann <arnd@arndb.de> >> >> Adding Ard Biesheuvel and Fangrui Song to Cc, so they can comment >> on the ARM_VECTORS_TEXT workaround. I don't understand enough of >> the details of what is going on here. >> > > Thanks for the cc > >> Full quote of the patch below so they can see the whole thing. >> >> If they are also happy with the patch, I think you can send it >> into Russell's patch tracker at >> https://www.armlinux.org.uk/developer/patches/info.php >> > > No, not happy at all :-) > > The resulting kernel does not boot (built with GCC or Clang). And the > patch is buggy (see below) > After applying .reloc .text, R_ARM_NONE, ., the resulting kernel boots well in QEMU. I tested it with the latest linux-next master branch and the mainline master branch. By the way, I used vexpress_defconfig for testing, it worked.
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