Hi Victor, On 18 November 2014 03:32, Victor Ascroft <victorascr...@gmail.com> wrote: > > On Monday 17 November 2014 11:58 AM, Simon Glass wrote: >> Hi Albert, >> >> On 16 November 2014 07:50, Albert ARIBAUD <albert.u.b...@aribaud.net> wrote: >>> Hello Simon, >>> >>> On Sat, 15 Nov 2014 15:10:47 -0700, Simon Glass <s...@chromium.org> >>> wrote: >>>> Hi Albert, >>>> >>>> On 15 November 2014 05:30, Albert ARIBAUD <albert.u.b...@aribaud.net> >>>> wrote: >>>>> Hello Simon, >>>>> >>>>> On Fri, 14 Nov 2014 18:56:07 -0700, Simon Glass <s...@chromium.org> >>>>> wrote: >>>>> >>>>>>> I believe you've built crt0.S for ARM, not Thumb. >>>>>> Yes, but I suspect that is a function of the build system. I checked >>>>>> the rest of U-Boot and most of it (including SPL) is Thumb 2. I >>>>>> suppose we could use Thumb 2 for crt0.S if all the instructions are >>>>>> supported. >>>>> Ok. Just in case, I'll run a check on whether crt0.S can be assembled >>>>> for Thumb and still wrk as expected. :) >>>>> >>>>> Do you have a list of source files which still build for ARM under >>>>> CONFIG_SYS_THUMB_BUILD? I' would prefer all of the code to be thumb for >>>>> consistence, except probably... exception :) entry points -- and even >>>>> these should be able to run in full Thumb 2. >>>> No I don't have a list, but it might be all assembler files. I don't >>>> see why cro0.S would be special. >>> Ok, so after some research, .S files voluntarily not assembled in Thumb >>> mode when -mthumb is defined in gcc because of this: >>> >>> Answer: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=27237 >>> >>> (summary: -mthumb for gcc means 'use thumb2', while it means 'use >>> dumb, 16-bit, thumb1' for GNU as, so this option is voluntarily not >>> passed on to GNU as. You have to use .thumb in the .S file instead.) >>> >>> Second: getting a successful, though quick'n'dirty, build with vectors.S >>> assembled in Thumb-2 mode needed surprisingly little change in >>> vectors.S. I tried this with mx53loco, and it only required: >>> >>> - adding '.syntax unified'; >>> >>> - adding a .thumb directive -- *after* the vectors per se, which >>> must still be assembled in ARM mode because current hardware >>> always executes exceptions vectors in ARM mode (1); >>> >>> - using '.balign' instead of '.balignl' which causes the >>> assembler to complain that it cannot fit an integer >>> number of '0xdeadbeef' in the filling space; >>> >>> - making macro get_bad_stack use lr instead of r13, which >>> Thumb does not allow in 'msr spsr,' instructions; >>> >>> - adding '.thumb_func' to all routines so that the linker makes >>> all references to them odd and therefore, cause the CPU to >>> enforce Thumb mode when branching to them. >>> >>> (1) although you *could* produce an ARM-based SoC that runs in >>> Thumb mode by default. In this case, you'd have to make the >>> vectors themselves Thumb too. >>> >>> Third: getting a successful *run* of the resulting file will require >>> some work which I'm not going to do without a good incentive :) -- and >>> so does producing a clean vectors.S, i.e. one which will assemble >>> correctly for both ARM and Thumb. > So to use the thumb build correctly, all the .S files have to be changed to > use > thumb instructions, by specifying the .thumb option?
No this is purely an optional idea. For me, the current Thumb support works fine on Exynos 54xx (which is Cortex A7/A15). The issue you are seeing may be specific to the A5 CPU, or your platform/toolchain. You could perhaps try a newer toolchain (e.g. linaro). crt0.S does not need to be in Thumb code. You could also check that -mthumb-interwork is defined correctly. You can use 'make V=1 ...' to see full verbose output. You could also disassemble the code sequence as I did to check it. I am assuming you have changed nothing else between building with Thumb and ARM. Regards, Simon _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
