[U-Boot] [PATCH] ARM: Fix __bss_start and __bss_end in linker scripts

[Tom Rini]

On Fri, Apr 05, 2013 at 07:32:54PM +0200, Beno??t Th??baudeau wrote:
> Hi Tom,
> 
> On Friday, April 5, 2013 6:00:30 PM, Tom Rini wrote:
> > On Fri, Apr 05, 2013 at 03:56:46PM +0200, Beno??t Th??baudeau wrote:
> > > Hi Albert,
> > > 
> > > On Friday, April 5, 2013 8:00:43 AM, Albert ARIBAUD wrote:
> > > > Hi Beno??t,
> > [snip]
> > > > IIUC, this future patch would increase the limit for SPL run-time size,
> > > > as the constant against which the ASS tests __bss_end for would
> > > > necessarily be greater than it is now. Correct? If so, this future
> > > > patch should not break any target, as it would loosen the constraint,
> > > > not tighten it.
> > > 
> > > Yes, it would either be the same or relaxed a bit, depending on the chosen
> > > option:
> > >  - Define CONFIG_SPL_BSS_MAX_SIZE and test against CONFIG_SPL_MAX_SIZE +
> > >    CONFIG_SPL_BSS_MAX_SIZE, the sum remaining the same as or being larger
> > >    than
> > >    currently, depending on the new values for CONFIG_SPL_MAX_SIZE and
> > >    CONFIG_SPL_BSS_MAX_SIZE.
> > >  - Define a new config meaning text + data + rodata + bss (e.g.
> > >    CONFIG_SPL_MAX_RAM_SIZE or CONFIG_SPL_MAX_MEM_FOOTPRINT), and just
> > >    replace
> > >    CONFIG_SPL_MAX_SIZE with it for the users of arch/arm/cpu/u-boot*.lds,
> > >    taking
> > >    care that this was the only meaning those users were giving to
> > >    CONFIG_SPL_MAX_SIZE.
> > > 
> > > The first option would probably be preferable, using the same value for
> > > CONFIG_SPL_MAX_SIZE, and a non-zero value for CONFIG_SPL_BSS_MAX_SIZE.
> > 
> > I think the problem is that Tegra really needs the second case as their
> > constraint is "must fit below next part of payload".  We can assume the
> > users of that linker script today care about footprint and update their
> > define I believe.  da850evm and the rest of the davinci platforms would
> > also be a case to convert to this, but the omap*/am3* platforms would
> > not.
> 
> Yes, then let's have an assert in arch/arm/cpu/u-boot*.lds with a
> different config name (as in option 2 above) just for Tegra, and
> another assert for CONFIG_SPL_MAX_SIZE against __bss_start.
> 
> And all users of CONFIG_SPL_MAX_SIZE should be checked to make sure
> that there is not another special case somewhere.

I didn't audit the PowerPC targets, but on ARM we have, roughly:
- Tegra (covered in Stephen's email, and in short, must include BSS in
  size check) which uses SPL_MAX_SIZE to include BSS
- OMAP*/AM3* which does not constrain BSS to SPL_MAX_SIZE
- DaVinci which must also constrain BSS to the initial RAM, but for
  different reasons.
- iMX which also uses SPL_BSS_MAX to cover the BSS separate from the
  rest of the program.

-- 
Tom
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