[PATCH] lds: align u-boot-nodtb with 8 bytes boundary

[Pali Rohár]

On Thursday 15 December 2022 06:24:16 Simon Glass wrote:
> Hi Eugen,
> 
> On Thu, 15 Dec 2022 at 03:58, Eugen Hristev <eugen.hristev at microchip.com> wrote:
> >
> > Newer DTC require that the DTB start address is aligned at 8 bytes.
> > In the u-boot.bin case, the u-boot-nodtb.bin is concatenated with the
> > DTB, but there is no alignment/padding to the next 8byte aligned address.
> > This causes the board to fail booting, because the FDT will claim
> > that the DTB inside u-boot.bin is not a valid DTB, it will fail with
> > -FDT_ERR_ALIGNMENT.
> > To solve this, have the u-boot binary `_end` aligned with 8 bytes.
> > The objcopy in the Makefile will create the u-boot-nodtb.bin and it has to
> > be truncated to 8 bytes to correspond to the u-boot.map file which will
> > have the `_end` aligned to 8 bytes.
> > The lds files which use devicetrees have been changed to align the `_end`
> > tag with 8 bytes.
> >
> > This patch is also a prerequisite to have the possibility to update the
> > dtc inside u-boot to newer versions (1.6.1+)
> >
> > Signed-off-by: Eugen Hristev <eugen.hristev at microchip.com>
> > ---
> > Hi,
> >
> > I could not test all affected boards, it's an impossible task.
> > I tried this on at91 boards which I have, and ran the CI on denx.
> > I cannot guarantee that no other boards are affected, so this patch is a bit
> > of an RFC.
> > If the u-boot-nodtb.bin does not have the size equal with the corresponding
> > one in u-boot.map, the binary_size_check will fail at build time with
> > something like this:
> >
> > u-boot.map shows a binary size of 502684
> > but u-boot-nodtb.bin shows 502688
> >
> > Thanks,
> > Eugen
> >
> >  Makefile                                    | 2 ++
> >  arch/arm/cpu/armv8/u-boot.lds               | 4 ++--
> >  arch/arm/cpu/u-boot-spl.lds                 | 1 +
> >  arch/arm/cpu/u-boot.lds                     | 1 +
> >  arch/arm/lib/elf_arm_efi.lds                | 5 +++++
> >  arch/arm/mach-at91/arm926ejs/u-boot-spl.lds | 2 +-
> >  arch/arm/mach-at91/armv7/u-boot-spl.lds     | 2 +-
> >  arch/arm/mach-zynq/u-boot-spl.lds           | 2 +-
> >  arch/mips/cpu/u-boot.lds                    | 2 +-
> >  arch/sandbox/cpu/u-boot.lds                 | 6 ++++++
> >  arch/sh/cpu/u-boot.lds                      | 2 ++
> >  board/ti/am335x/u-boot.lds                  | 1 +
> >  tools/binman/test/u_boot_binman_embed.lds   | 2 +-
> >  13 files changed, 25 insertions(+), 7 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index 9d84f96481..b4d387bcce 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -1317,6 +1317,8 @@ endif
> >
> >  u-boot-nodtb.bin: u-boot FORCE
> >         $(call if_changed,objcopy_uboot)
> > +# Make sure the size is 8 byte-aligned.
> > +       @truncate -s %8 $@
> >         $(BOARD_SIZE_CHECK)
> 
> I agree this line is needed, since otherwise we will only get 4-byte
> alignment.

Hello! I do not fully agree that this line is needed.

The whole issue is about DTB binary and its offset. So code/Makefile
which construct u-boot.bin should be fixed and not u-boot-nodtb.bin.

> But it would be better if we could have the linker scripts
> fill bytes out to the required alignment. Is that possible?

I already investigated this. LD linker and objcopy (at least older
version in Debian 10) drops trailing zero bytes in raw binary output.

You can specify zero bytes in the linker script and they are filled in
ELF or COFF output. But not in raw binary, which u-boot.bin is.

So it could be possible to extract "correct" size from ELF binary and
call truncate on raw binary generated from objcopy.



I already hit this trailing-zeros issue for powerpc and I fixed it in:
7696b80ec5e9 powerpc: mpc85xx: Fix loading U-Boot proper from SD card in SPL
b898f6a6db76 powerpc: mpc85xx: Fix CONFIG_OF_SEPARATE support for NOR booting
e8c0e0064c8a powerpc: mpc85xx: Fix CONFIG_OF_SEPARATE support

All those commits re-align output to just 4 bytes, not more.

So Makefile change in this proposed patch is going to break all
powerpc/mpc85xx boards.