[PATCH u-boot v2 00/38] U-Boot LTO (Sandbox + Some ARM boards)

[Harald Seiler]

Hi Marek,

On Fri, 2021-03-12 at 11:33 +0100, Marek Behún wrote:
> Hello,
> 
> I am sending version 2 of patches adding support for LTO to U-Boot.
> 
> This series was tested by Github/Azure CI at
>   https://github.com/u-boot/u-boot/pull/57
> 
> Code reduction is on average 4.23% for u-boot.bin and 13.58% for
> u-boot-spl.bin.
> 
> I am currently running a build test for all 1077 ARM defconfigs.
> Of the first 232 defconfigs, 2 are failing when LTO is enabled
> (chromebook_jerry and chromebook_speedy). Note that this series
> only enables LTO for tested boards.
> 
> Changes since v1:
> - remove patches applied into u-boot-marvell
> - added Reviewed-by tags
> - addressed some issues discovered by Bin Meng, Marek Vasut,
>   Heinrich Schuchardt
> - added more ARM boards (thanks to Adam Ford, Tim Harvey and Bin Meng)
> - removed --gc-sections for ARM if internal libgcc is used
> - remove -fwhole-program in final LTO LDFLAGS
> - declared all 4 functions (memcpy, memset, memcmp, memmove) __used,
>   (these are mentioned in GCC man page for option -nodefaultlibs that
>    the compiler may generate; this seems to be a bug in GCC that linking
>    fails with LTO even if these functions are present, because the
>    symbols can be renamed on some targets by optimization)

I'm hitting a compiler error when building with imx6q_logic_defconfig:

  real-ld: error: no memory region specified for loadable section `.note.gnu.build-id'

It seems this is caused by calling the linker through a gcc invocation
which adds a `--build-id` commandline flag.  I think the linker script
which is used for SPL in this case (arch/arm/mach-omap2/u-boot-spl.lds)
isn't properly set up to deal with a build-id.

I'm not sure how to deal with this.  One could either add
`--build-id=none` to the GCC commandline to suppress generation of this
section entirely (it is not emitted in non-LTO builds right now anyway) or
include it in .text in said linker script so it is visible on the target.
What do you think?

I should note that I am using a Yocto-generated toolchain.  I suppose most
standard toolchains' behavior regarding the `--build-id` flag probably
differs.

Regards,
-- 
Harald