On Fri, Mar 05, 2021 at 09:34:42PM +0800, Bin Meng wrote:
Hi Marek,
On Fri, Mar 5, 2021 at 2:17 AM Marek Behun marek.behun@nic.cz wrote:
On Thu, 4 Mar 2021 18:57:11 +0800 Bin Meng bmeng.cn@gmail.com wrote:
Hi Marek,
On Wed, Mar 3, 2021 at 12:13 PM Marek Behún marek.behun@nic.cz wrote:
Using thin archives instead of incremental linking
- saves disk space
- works better with dead code elimination
- prepares for potential LTO
The commit message is a little bit confusing. This commit actually does 2 things: don't do incremental linking (using --whole-archive), and use thin archive (passing T to ar). I believe they are for different purposes, so we cannot say "using thin archives instead of incremental linking".
-Wl,--start-group $(patsubst $(obj)/%,%,$(u-boot-spl-main)) \$(patsubst $(obj)/%,%,$(u-boot-spl-platdata)) -Wl,--end-group \
-Wl,--whole-archive $(patsubst $(obj)/%,%,$(u-boot-spl-main)) -Wl,--no-whole-archive \-Wl,--start-group $(patsubst $(obj)/%,%,$(u-boot-spl-platdata)) -Wl,--end-group \u-boot-spl-platdata is still within --start-group, --end-group, is this intentional?
I confess that I did not really study these options, I have made these changes according to old LTO patches for Linux. But you are right that it does not make sense. I have fixed this for the next version of this patch.
Is P required to make everything work?
It is not. Removed in next version.
I did more investigation on this.
The Linux kernel specially added P to ar, in below commit: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
So it looks like we should keep P here?
But I don't get the point of switching to thin archives. Based on my experiment, LTO does not rely on thin archives. The Linux kernel did not introduce thin archives for LTO. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
So technically it would just be part of dealing with the backlog of kbuild-resync to take it in this series I guess.