On Mon, Aug 08, 2022 at 04:34:00PM +0200, Rasmus Villemoes wrote: > Looking at one of the .o.cmd files, I noticed that we build arm64 with > both -ffixed-r9 and -ffixed-x18. The latter is obviously what we use for > gd, but the former doesn't seem to serve any purpose on arm64, and just > seems to be an accident of the makefile fragment organization. > > When I just remove -ffixed-r9 from arch/arm/config.mk, it builds and > boots just fine (a real patch would of course do some ifndef > CONFIG_ARM64 thing). The code does change, generally of the form "use x9 > instead of x10, x10 instead of x11" etc., i.e. the expected register > allocation changes. But the total space saving from having that extra > scratch reg is almost non-existing; a mere 44 bytes for u-boot proper; > apparently aarch64 has plenty of scratch registers even if one is > reserved-and-never-used. > > Still, it's somewhat confusing, so if for some reason this is really > needed in some cases (calling into some 32 bit firmware???), I'd like a > comment somewhere.
I strongly suspect this is just a remnant of how the Makefile logic is, and that since nothing failed with -ffixed-r9 it just kept being used. -- Tom
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