On 01/03/16 15:42, Ben Avison wrote:
Hi folks,As you'll probably have heard, Raspberry Pi have launched a new board based on the ARMv8 Cortex-A53. One of the main compatibility issues remaining is that anything built on UnixLib is rather unlikely to work. I did a bit of investigating and found the problem was with the use of SWP in __pthread_disable_ints in libunixlib/pthread/_ints.s (although the lack of pushing a stack frame means that blame will be attributed elsewhere in backtraces). There are a couple of other instances of SWP elsewhere in UnixLib. Now, we're now living in a world where there is no one simple code sequence which can do atomic operations from USR mode across all CPUs from ARMv2(a) to ARMv8. A crude solution would be to replace LDR a1, .L0 @=__ul_global PICEQ "LDR a1, [a2, a1]" ADD a1, a1, #GBL_PTH_WORKSEMAPHORE MOV a3, #1 SWP a2, a3, [a1] @ From this point onwards we will not be interrupted by the callback ADD a2, a2, #1 STR a2, [a1] MOV pc, lr with something like LDR a1, .L0 @=__ul_global PICEQ "LDR a1, [a2, a1]" ADD a3, a1, #GBL_PTH_WORKSEMAPHORE MOV a1, #0 SWI XOS_ReadPlatformFeatures MOVVS a1, #0 TST a1, #1<<12 @ does the CPU support LDREX? BNE 1f @ SWP version MOV a1, #1 SWP a2, a1, [a3] @ From this point onwards we will not be interrupted by the callback ADD a2, a2, #1 STR a2, [a3] MOV pc, lr 1: @ LDREX version LDREX a2, [a3] ADD a2, a2, #1 STREX a1, a2, [a3] TEQ a1, #1 BEQ 1b MOV pc, lr and something similar for the other instances of SWP. However, I can't help thinking it would be neater to do the ReadPlatformFeatures once somewhere very early on in library initialisation and store the result in library static data somewhere. This is where I suspect my lack of knowledge of UnixLib internals means that I expect someone more familiar with it could knock up a solution far quicker - so, any takers?
Yes, I'll have a go when I get a chance. Thanks for the sample code, that should make it easier. Lee. _______________________________________________ GCCSDK mailing list gcc@gccsdk.riscos.info Bugzilla: http://www.riscos.info/bugzilla/index.cgi List Info: http://www.riscos.info/mailman/listinfo/gcc Main Page: http://www.riscos.info/index.php/GCCSDK
