[PATCH-next v2] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION
liuyuntao (F)
liuyuntao12 at huawei.com
Fri Mar 8 22:14:49 PST 2024
On 2024/3/8 21:15, Arnd Bergmann 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 at 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.
>
Thanks for the tests, CONFIG_LD_DEAD_CODE_DATA_ELIMINATION and
CONFIG_TRIM_UNUSED_KSYMS do indeed result in a significant improvement.
I found that arm32 still doesn't support CONFIG_LTO_CLANG. I've done
some work on it, but without success. I'd like to learn more about the
CONFIG_LTO_CLANG patch. Do you have any relevant links?
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