On Mon, Mar 8, 2021 at 7:00 PM Pali Rohár pali@kernel.org wrote:
On Monday 08 March 2021 18:44:58 Bin Meng wrote:
On Mon, Mar 8, 2021 at 6:11 PM Marek Behun marek.behun@nic.cz wrote:
On Mon, 8 Mar 2021 17:16:03 +0800 Bin Meng bmeng.cn@gmail.com wrote:
Hi Marek,
On Sun, Mar 7, 2021 at 12:26 PM Marek Behún marek.behun@nic.cz wrote:
Currently we use incremental linking (ld -r) to link several object files from one directory into one built-in.o object file containing the linked code from that directory (and its subdirectories).
Linux has, some time ago, moved to thin archives instead.
Thin archives are archives (.a) that do not really contain the object files, only references to them.
Using thin archives instead of incremental linking
- saves disk space
- apparently works better with dead code elimination
- makes things easier for LTO
The third point is the important one for us. With incremental linking there are several options how to do LTO, and that would unnecessarily complicate things.
On the other hand, by using thin archives we can make (via the --whole-archive use flag) the final linking behave as if we passed all the object files from the archives to the linking program as arguments.
I don't think --whole-archive is required for LTO to work.
It is. Linking fails if it is not used, for example for nokia_rx51_defconfig.
Could you investigate why? Is this due to missing marking some variables/functions as __used?
See email Message-ID: 20210306210045.pn3vzuarh23poxuv@pali for details.
Looking at 20210306210045.pn3vzuarh23poxuv@pali, the error you reported seemed to be caused by not passing P to ar, as Marek replied to you.
Regards, Bin