Re: [PATCH] Add warning above get_ram_size

[Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>]

On 12:45 Sat 16 Feb     , Alexander Shiyan wrote:
> ...
> > > >>> --- a/common/memsize.c
> > > >>> +++ b/common/memsize.c
> > > >>> @@ -33,6 +33,9 @@
> > > >>>   * Check memory range for valid RAM. A simple memory test determines
> > > >>>   * the actually available RAM size between addresses `base' and
> > > >>>   * `base + maxsize'.
> > > >>> + *
> > > >>> + * This function modifies the RAM. Do not use it if you're running from
> > > >>> + * the RAM you are going to detect!
> > > >>>   */
> > > >>
> > > >> Actually, I don't see how it modifies the RAM, at least permanently. The
> > > >> values it erase are backed up, and there's no concurrency at barebox
> > > >> level, so we are sure that the value saved will still be the one that
> > > >> would need to be backed up at the end of the function, right?
> > > > 
> > > > Yes, it restores the values, but how do you make sure the function does
> > > > not modify the instructions you are currently executing? You need bad
> > > > luck to hit this, but sooner or later this will happen.
> > > 
> > > Ah, yes, this would be nasty indeed. Is there a way to know the end
> > > address of barebox into RAM ? or the address it has been loaded to and
> > > the size of its binary, so that we can just check the part that doesn't
> > > hold barebox?
> > 
> > See include/asm-generic/sections.h. You have to avoid modifying
> > everything between _text and __bss_stop. I haven't looked how exactly
> > get_dram_size works. Normally this function would have to test every
> > location at a power of 2, that would be:
> > 
> > 1 2 4 ... 64MiB 128MiB
> > 
> > It seems you have to make sure that your binary does not cross a power
> > of 2 boundary, then you should be safe.
> 
> Let's put "get_ram_size" function in a separate section inside .text. Then we
> can at least make runtime warning about placing this section inside our
> tested region.

we have 2 case

1: we run from the relocated position
2: we run before relocation

in any case you need to exclude where running from or just need to be carefull
when use it

Best Regards,
J.
> 
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