Hi Stefan,
you wrote:
Currently do_bootelf() disables data cache just before passing control to the entry point:
/* * QNX images require the data cache is disabled. * Data cache is already flushed, so just turn it off. */ if (dcache_status ()) dcache_disable ();With this piece of code present I'm seeing strange effects (corrupt data access, hangs) in standalone apps running from the ELF envelope.
What platform are you testing on? PPC? If yes, which one?
Yes, 85xx.
A pure binary made of this same ELF works without problems. Contrary to the comment above, there's no quarantee in do_bootelf() code flow that all data cache has been flushed and it seems there needs to be flush_data_cache() executed before the disable.
dcache_disable() should flush the dcache itself before disabling it. At least this is the implementation I have seen on 405 and IIRC other PPC platforms.
Indeed, in certain cases it does actually (e.g. 86xx), but it's not uniform unfortunatelly. In my case (85xx) dcache_disable() does not flush the cache before disabling.
- Does it really hold true that QNX requires d-cache disabled upon passing
control to it?
- If so, this is a custom QNX thing that belongs to do_bootm_qnxelf() and
should be handled there and not at the common ELF handling level.
Hmmm. I think that calling applications and especially OS'es is more safe with caches disabled then with caches enabled.
Yeah, after a second thought I tend to agree. Maybe the way to go is doing data cache flush from within dcache_disable() properly i.e. bring it in for arch variations that don't do it currently like 85xx... Actually to confirm my observations I tested a working patch that flushes d-cache at cache_disable() just like 86xx and it works for me, this is: my problems disappear. Do you think this is a better option?
kind regards, Rafal