[PATCH] arch: arm: force 4K page alignment in linker

[Sam Day]

Hey Peter,

On Friday, 29 May 2026 at 8:18 PM, Peter Robinson <pbrobinson at gmail.com> wrote:

> Hi Sam,
> 
> > Since 5c71f8110, the u-boot.elf produced by dragonboard410c_defconfig no
> > longer fits in the 1MiB aboot partition it is intended for.
> >
> > To be precise, this issue occurs on toolchains that have a linker with a
> > COMMONPAGESIZE > 4K. Since u-boot is hardcoded for 4K granules, we
> > ensure that the linker doesn't try to align to anything larger than
> > that, otherwise we're just filling our ELFs with a bunch of useless
> > zeros.
> 
> Is this just applicable to ELFs or can it be applied more widely?

I'm not completely sure :)

These linker options control ld's constants [1]. COMMONPAGESIZE is used
to align sections in arm32/arm64 linker scripts [2]. Whether this affects
anything else besides that is not fully clear to me.

> 
> > Suggested-by: Stephan Gerhold <stephan.gerhold at linaro.org>
> > Signed-off-by: Sam Day <me at samcday.com>
> Tested-by: Peter Robinson <pbrobinson at gmail.com>
> 
> Tested on a Rock960 where the elf output went from 9498864 to 9437424

This isn't much of a change at all, I wonder what toolchain you're using,
and what its default COMMONPAGESIZE is? You can run the snippet below to
find out.

```sh
echo 'SECTIONS { cps = CONSTANT(COMMONPAGESIZE); }' > /tmp/pg.lds && 
  echo 'int x;' | aarch64-linux-gnu-gcc -x c - -c -o /tmp/pg.o && 
  aarch64-linux-gnu-ld -T /tmp/pg.lds -o /tmp/pg.elf /tmp/pg.o && 
  aarch64-linux-gnu-nm /tmp/pg.elf \
  | awk '/cps/{print strtonum("0x"$1), "("$1")"}'
```

[1]: https://sourceware.org/binutils/docs/ld/Symbolic-Constants.html
[2]: https://github.com/search?q=repo%3Au-boot%2Fu-boot%20COMMONPAGESIZE&type=code

Cheers,
-Sam

> 
> > ---
> >  arch/arm/config.mk | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/arch/arm/config.mk b/arch/arm/config.mk
> > index a7eff84a267..bce9a31e966 100644
> > --- a/arch/arm/config.mk
> > +++ b/arch/arm/config.mk
> > @@ -112,6 +112,14 @@ endif
> >  # needed for relocation
> >  LDFLAGS_u-boot += -pie
> >
> > +ifeq ($(CONFIG_ARM64),y)
> > +# U-Boot uses fixed 4K granules, so we force the linker to match.
> > +# Otherwise, we're subject to toolchain preferences, (e.g Fedora's
> > +# aarch64-linux-none toolchain selects 64K granules) and we end up wasting
> > +# a lot of space in ELFs with MMU_PGPROT enabled.
> > +LDFLAGS_u-boot += -z common-page-size=0x1000 -z max-page-size=0x1000
> > +endif
> > +
> >  #
> >  # FIXME: binutils versions < 2.22 have a bug in the assembler where
> >  # branches to weak symbols can be incorrectly optimized in thumb mode
> >
> > ---
> > base-commit: 987907ae4bcc5d6055bdf7d318a3edf53e14d5fa
> > change-id: 20260528-4k-page-alignment-6cb594a073b0
> >
> > Best regards,
> > --
> > Sam Day <me at samcday.com>
> >
> >
>