From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steve Rae Date: Mon, 9 Jun 2014 13:45:50 -0700 Subject: [U-Boot] [PATCH] arm: Allow u-boot to run from offset base address In-Reply-To: References: <1400105145-6628-1-git-send-email-drambo@broadcom.com> <1400107265.16796.8.camel@yellow> <5374CD55.3010703@broadcom.com> <20140515152119.9939F38047D@gemini.denx.de> <5374E64B.1060104@broadcom.com> <20140515191957.74A853804B6@gemini.denx.de> <538367B7.5090108@broadcom.com> <538D18C5.206@broadcom.com> Message-ID: <53961CFE.4090106@broadcom.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de On 14-06-09 03:23 AM, Albert ARIBAUD wrote: > Hi Darwin, > > On Mon, 2 Jun 2014 17:37:25 -0700, Darwin Rambo > wrote: > >> >> >> On 14-06-02 12:26 AM, Albert ARIBAUD wrote: >>> Hi Darwin, >>> >>> On Mon, 26 May 2014 09:11:35 -0700, Darwin Rambo >>> 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, > Perhaps an oversimplified example of the current code would help to explain this better: scenario #1: CONFIG_SYS_TEXT_BASE 0x88000000 vectors: .align 11 /* exception vectors need to be on a 0x800 byte boundary */ compile/linker produces (before relocation): _start symbol is at 0x88000000 vectors symbol is at 0x88000800 the relocation offset is: 0x77f9b000 therefore, after relocation: _start symbol is at 0xfff9b000 (0x88000000+0xfff9b000) vectors symbol is at 0xfff9b800 (0x88000800+0x77f9b000) scenario #2: CONFIG_SYS_TEXT_BASE 0x88000020 vectors: .align 11 /* exception vectors need to be on a 0x800 byte boundary */ compiler/linker produces (before relocation): _start symbol is at 0x88000020 vectors symbol is at 0x88000800 the relocation offset is: 0x77f9afe0 therefore, after relocation: _start symbol is at 0xfff9b000 (0x88000020+0x77f9afe0) vectors symbol is at 0xfff9b7e0 (0x88000800+0x77f9afe0) Note that in scenario #2, after relocation, the vectors are not on a 0x800 byte boundary anymore. Thanks, Steve