[PATCH u-boot v4 13/36] build: use thin archives instead of incremental linking

[Simon Glass]

On Thu, 20 May 2021 at 05:25, Marek Behún <marek.behun at 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.
>
> We have to use the --whole-archive/--no-whole-archive linking option
> instead of --start-group/--end-group, otherwise linking may fail because
> of unresolved symbols, or the resulting binary will be unusable.
>
> We also need to use the P flag for ar, otherwise final linking may fail.
>
> Signed-off-by: Marek Behún <marek.behun at nic.cz>
> ---
>  Makefile               |  4 ++--
>  arch/sandbox/config.mk | 10 +++++++---
>  scripts/Makefile.build | 16 ++++++++--------
>  scripts/Makefile.spl   |  4 ++--
>  4 files changed, 19 insertions(+), 15 deletions(-)

Reviewed-by: Simon Glass <sjg at chromium.org>