Hello,
I have managed to add support for building U-Boot with LTO (with GCC) in a rather sane way (in LOC changed).
This series and its follows will also be available at https://github.com/elkablo/u-boot branch lto.
I have tested these builds on Turris Omnia, Turris MOX and on Nokia N900 (via the test/nokia_rx51_test.sh script). For other tests I have created a pull-request on github to trigger CI (https://github.com/u-boot/u-boot/pull/57) For some reason it is waiting now, maybe Azure is not working or something.
My tests on Omnia and MOX show that U-Boot boots sucessfully, and basic commands seem to work. But of course something broken due to LTO may be found later.
So for all of you that are interested and have an ARM board, please test this on your boards by enabling CONFIG_LTO option. Also please report code size reductions. (Chris Packham reports an error related to jobserver, so if `make -jN` produces an error, please try without the `-jN` flag.)
I have only tested with gcc-10. There are still some warnings printed, like: bfd plugin: invalid symbol type found but these don't seem to matter. I will look into this later.
Here are some results by how much code size reduced. Note that SPL binary seems to gain more code reduction (15.4 % on average) than main binary (4.5 % on average).
I guess this is because of how drivers are written. The optimizer cannot know which code paths won't be used, since it does not see the device tree. Maybe this could be somehow integrated with Simon's work on OF_PLATDATA_INST in the future, to make the compiler optimize out unused code paths in drivers by understanding the device tree.
u-boot.bin u-boot-spl.bin
clearfog 4.34 % 19.0 KB 13.55 % 16.8 KB controlcenterdc 4.79 % 24.2 KB 16.27 % 21.9 KB db-88f6820-amc 4.23 % 25.0 KB 16.17 % 22.9 KB db-88f6820-gp 4.42 % 22.1 KB 17.00 % 23.8 KB helios4 4.32 % 18.9 KB 13.70 % 16.8 KB nokia_rx51 6.11 % 16.5 KB turris_mox 4.17 % 31.8 KB turris_omnia 4.32 % 30.2 KB 14.91 % 16.6 KB x530 3.93 % 30.0 KB 16.26 % 23.4 KB
Marek
Marek Behún (12): build: use thin archives instead of incremental linking sandbox: errno: avoid conflict with libc's errno linker_lists: declare entries and lists externally visible efi_loader: fix warning when linking with LTO binman: declare symbols externally visible build: support building with Link Time Optimizations arch: sandbox: make LTO available sandbox: build with LTO ARM: make gd a function for LTO string: make memcpy() visible to fix LTO linking errors arch: ARM: make LTO available Nokia RX-51: build with LTO
Kbuild | 2 ++ Kconfig | 19 +++++++++++++++++++ Makefile | 28 +++++++++++++++++++++++++++- arch/Kconfig | 2 ++ arch/arm/include/asm/global_data.h | 2 +- arch/arm/lib/Makefile | 2 ++ arch/sandbox/config.mk | 10 +++++----- configs/nokia_rx51_defconfig | 1 + configs/sandbox64_defconfig | 1 + configs/sandbox_defconfig | 1 + configs/sandbox_flattree_defconfig | 1 + configs/sandbox_spl_defconfig | 1 + include/binman.h | 1 + include/binman_sym.h | 4 ++-- include/efi_loader.h | 4 ++-- include/errno.h | 8 +++++++- include/linker_lists.h | 6 ++++-- lib/efi_loader/Makefile | 2 +- lib/errno.c | 4 +++- lib/string.c | 3 ++- scripts/Makefile.build | 5 ++--- scripts/Makefile.lib | 3 +++ scripts/Makefile.spl | 20 ++++++++++++++++---- 23 files changed, 106 insertions(+), 24 deletions(-)