Hi Darwin, On Mon, 2 Jun 2014 17:37:25 -0700, Darwin Rambo <dra...@broadcom.com> wrote:
> > > On 14-06-02 12:26 AM, Albert ARIBAUD wrote: > > Hi Darwin, > > > > On Mon, 26 May 2014 09:11:35 -0700, Darwin Rambo <dra...@broadcom.com> > > wrote: > > > >> Hi Albert, > >> > >> The previous stage bootloader (which I had no control over) wanted it's > >> header to be aligned to a 512 byte MMC block boundary, presumably since > >> this allowed DMA operations without copy/shifting. At the same time, I > >> didn't want to hack a header into start.S because I didn't want to carry > >> another downstream patch. So I investigated if I could shift u-boot's > >> base address as a feature that would allow an aligned header to be used > >> without the start.S patch. > >> > >> I know that a custom header patch to start.S would work, and that a > >> header plus padding will also work. But I found out that you can align > >> the base on certain smaller offsets if you keep the relocation offset at > >> nice boundaries like 0x1000 and if the relocation offset is a multiple > >> of the maximum alignment requirements of the image. > >> > >> The original patch I submitted didn't handle an end condition properly, > >> was ARM64-specific (wasn't tested on other architectures), and because > >> the patch was NAK'd, I didn't bother to submit a v2 patch and consider > >> the idea to be dead. I'm happy to abandon the patch. I hope this helps. > > > > Thanks. > > > > If I understand correctly, your target has a requirement for storing > > the image on a 512-byte boundary. But how does this affect the loading > > of the image into RAM, where the requirement is only that the vectors > > table be 32-bytes aligned? I mean, if you store the image in MMC at > > offset 0x200 (thus satisfying the 512-byte boundary requirement) and > > load it to, say, offset 0x10020 in RAM, how is it a problem for > > your target? > > > > If my example above inadequately represents the issue, then can you > > please provide a similar but adequate example, a failure case scenario, > > so that I can hve a correct understanding of the problem? > > Hi Albert, > > The constraints I have that I can't change, are that > - the 32 byte header is postprocessed and prepended to the image after > the build is complete > - the header is at a 512 byte alignment in MMC > - the header and image are copied to SDRAM to an alignment like > 0x88000000. Thus the u-boot image is linked at and starts at 0x88000020. > - the vectors need to be 0x800 aligned for armv8 (.align 11 directive) So far, so good -- I understand that the link-time location of the vectors table is incorrect. > So the failure case is that when the relocation happens, it relocates to > a 0x1000 alignment, say something like 0xffffa000. The relocation offset > is not a multiple of 0x1000 (0xffffa000 - 0x88000020) and the relocation > fails. What does "relocation fails" mean exactly, i.e., where and how exactly does the relocation code behave differently from expected? I'm asking because I don't understand why the relocation offset should be a multiple of 0x1000. > Adjusting the relocation offset to a multiple of 0x1000 (by > making the relocation address end in 0xNNNNN020) fixes the issues and > allows u-boot to relocate and run from this address without failing. I > hope this helps explain it a bit better. I do understand, however, that if the relocation offset must indeed be a multiple of 0x1000, then obviously the vectors table will end up as misaligned as it was before relocation. Also, personally I would like it if the vectors table was always aligned as it should, and there are at least three other boards which require a prefix/header before their vectors table, as Masahiro (cc:) indicated recently, so that makes the problem a generic one: how to properly integrate a header in-image (as opposed to an out-of-image one, which is just a matter of doing a 'cat', so to speak. Therefore I'd like a generic solution to this, where the header is prepended *and* aligned properly without breaking the start symbol alignment constraints. This /might/ be possible by cleverly adding a '.header' or '.signature' section to the linker script, possibly doing a two-stage link; but this should not require the source code to contain ad hoc relocation tricks. Let me tinker with it in the next few days; I'll try and come up with a clean and generic solution to this "in-code header" question. Thanks again for your explanation! > Best regards, > Darwin Amicalement, -- Albert. _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
