On Fri, 12 Mar 2021 16:11:13 +0100 Harald Seiler <h...@denx.de> wrote:
> On Fri, 2021-03-12 at 16:07 +0100, Harald Seiler wrote: > > On Fri, 2021-03-12 at 15:26 +0100, Marek Behun wrote: > > > On Fri, 12 Mar 2021 15:21:05 +0100 > > > Harald Seiler <h...@denx.de> wrote: > > > > > > > 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, > > > > > > I encountered this with Debian's cross toolchain, but since this did > > > not happen on my station with Gentoo crossdev toolchain, nor on Azure > > > CI, I ignored it. > > > > > > What is the purpose of --build-id? Why do people use it? > > > > I'm not entirely sure but I think it acts as a unique identifier for > > a certain binary. So you can match up a core-dump with its debug info for > > example. > > > > But I am unsure if anyone in the firmware space is actively using this > > feature... At least U-Boot does not actually include the build-id on the > > target - it is not generated for SPL at all and U-Boot proper only > > contains it in the ELF file, it is not exported into the raw binary. > > This is the origin of --build-id: > > https://fedoraproject.org/wiki/Releases/FeatureBuildId > Tom, do we want build-id stored in binaries? Maybe it can be useful for something. Marek
