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

[Simon Glass <sjg@chromium.org>]

Hi Mark,

On Fri, 30 Dec 2022 at 12:11, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
>
> > From: Simon Glass <sjg@chromium.org>
> > Date: Fri, 30 Dec 2022 11:51:05 -0600
> >
> > Hi Pali,
> >
> > On Fri, 30 Dec 2022 at 09:32, Pali Rohár <pali@kernel.org> wrote:
> > >
> > > On Thursday 22 December 2022 10:49:58 Tom Rini wrote:
> > > > On Fri, Dec 16, 2022 at 01:13:07AM +0100, Pali Rohár wrote:
> > > > > 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@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@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.
> > > >
> > > > We should indeed not force u-boot-nodtb.bin itself to be an 8 byte
> > > > aligned size, yes.
> > > >
> > > > > > 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.
> > > >
> > > > This however needs a follow-up.  By spec, device tree binaries must
> > > > start at an 8 byte aligned address, not 4.  Yes, 4 is clearly functional
> > > > in this case, but when we update to a newer libdtc that finally enforces
> > > > this check we'll have a problem.
> > >
> > > In https://lore.kernel.org/u-boot/20221217235913.w7ihsktbplbp2j7z@pali/
> > > I proposed how to extend Makefile rule to generate u-boot-nodtb.bin with
> > > all required paddings. However this (enforcing u-boot-nodtb.bin to be 8
> > > byte aligned) is not we think that is the correct way. But I do not have
> > > any other option yet how to solve this problem.
> >
> > See the other thread [1] on this
> >
> > >
> > > I think that the source of this issue is that we are not putting DTB
> > > binary into ELF binary (so objcopy would be able to easily generate
> > > final u-boot.bin). And instead trying to simulate joining more binary
> > > files (u-boot-nodtb.bin and DTB binary) into one _without_ information
> > > how to do it correctly. But we already have this information in linker
> > > script and also in ELF binary.
> >
> > The DTB can come later, during packaging, or may be updated in that
> > step. Or there may multiple DTBs and SPL can decide which to use.
> > Overall the DTB is considered separate from the code by design, so
> > that it is possible to build one U-Boot that supports multiple boards.
> >
> > That is why we don't allow DTB in the ELF.
>
> Repeating that statement doesn't make it true.  We have an option for
> this (OF_EMBED) and that option is legitimately used by several
> "boards" in cases where U-Boot is used as in combination with
> "firmware" that expects a valid ELF binary as its payload.

We have this problem with EFI, and the approach is to embed an ELF
'stub' with a u-boot.bin payload.

But a better way would be to update that 'firmware' to pass the DTB to
U-Boot using standard passage.

>
> That said, I do think that OF_SEPARATE should be used whenever
> possible.  And in that case it should be the tool that combines the
> various components into a single binary that makes sure the DTB is
> properly aligned.

OK good. That seems to be where we are heading.

Regards,
Simon