On Tue, Jul 9, 2019 at 11:17 AM Russell King - ARM Linux admin <li...@armlinux.org.uk> wrote: > On Tue, Jul 09, 2019 at 10:41:05AM +0200, Linus Walleij wrote: > > I guess this brings up the old question whether the compiler should > > be worked around or just considered immature, but as it happens this > > other day I was grep:ing around to find "the 8 NOP" that is so > > compulsively inserted in ARM executables (like at the very start of > > the kernel execution) > > The NOPs at the start of the kernel executable have nothing what so ever > to do with this. They are there to align the kernel entry with the old > a.out format that was used (which had a 32 byte header). Consequently, > there are boot loaders around that jump to 32 bytes into the kernel > header.
Wow! Finally the puzzle pieces come together. And it makes a lot of sense. > There are other places that we insert 10 NOPs (at cpu_relax()) due to a > CPU errata (otherwise a tight loop basically stalls other CPUs.) Pretty interesting too! I try to learn a bit more intrinsics of the Arm architecture (been doing assembly experiments recent days) so getting to know things like this is very valuable. Yours, Linus Walleij
