On Wed, 2009-10-07 at 01:07 +0200, Wolfgang Denk wrote: > Dear Peter Tyser, > > In message <1254862383.24664.2742.ca...@localhost.localdomain> you wrote: > > > > What's the advantage of having the bss not be located next to U-Boot? > > One advantage is that we might chose the same address for all boards, > and eventually for all Power processor families.
We could achieve this wherever we end up putting the bss. eg if people think putting the bss right after the u-boot image is best, we can update the 44x linker script, etc to do the same thing. I think this discussion is applicable to most any PPC board. > One disadvantage is that we need to relocate it separately, or we will > have a gap in the RAm memory map which is IMO not acceptable. What does "relocating the bss separately" entail? > > The big disadvantage of picking an arbitrary address for the bss is that > > there's now 1 more magical section of SDRAM that the user needs to know > > shouldn't be used. I already field enough question from people that > > Why should it not be used? You seem to be pretty fixed on that idea, > which is wrong. No code will ever be written to RAM at list location. When I say user, I'm refering to an end user, eg a customer. Not a developer. For arguments sake, lets say we developers put the bss at a "fixed (random, non-zero) address" of 0x80000. A user tftps an image to 0x80000 and suddenly their board starts acting up. > In the current setup, we don't write any code to RAM at 0x0 either. Right, and this limitation causes headaches. I personally get lots of questions from customers about why their board hangs when they tftp an image to 0x0. In a perfect world we'd only have 1 reserved section of memory which contained the interrupt vectors, text, bss, malloc, stack, etc. > > corrupt their exception vectors or stack/malloc pool/u-boot code, I > > don't want to add more bss questions:) Its crappy to have 2 sections of memory that a user has to know not to touch, I don't want to have 3:) Maybe I'm not understanding your suggestion "to chose a fixed (random, non-zero) address" for the bss. That implies to me we choose an address low memory (eg 0x10000) and put the bss there. I think it'd be more plausible for someone to blow this away accidentally than high memory by U-Boot, and you also couldn't use any data stored in the bss after you blow it away, eg right before jumping to a linux kernel. Best, Peter _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
