On Wed, 2012-09-05 at 16:32 +0800, Guodong Xu wrote: > Hi, all > > This patch is about adding codes to turn on CCI compatible with all platforms, A15 > x4, and big.LITTLE, etc. > > With this patch, a Secure vector table is installed, with which the > data abort for accessing CCI on boards where it doesn't exist can be > captured and handled. Rather than always ignoring data aborts, it might be nice to have a separate function to try and read an address and have the data abort handler, check for that function explicitly. Then if the abort was caused by a different instruction do something (like execute an invalid instruction) so that the data abort gets noticed rather than ignored. E.g. @ @ Turn on CCI snoops @ ldr r4, =0x2c090000 add r0, r4, #0xc @ status reg bl try_read bne no_cci ... no_cci: ... try_read: mov r12, #0 try_read_may_fault: ldr r0, [r0] cmp r12, #0 bx lr @ data abort handling ldr r12, =try_read_may_fault+8 cmp lr, r12 @ if faulting instruction is try_read_may_fault subeqs pc, lr, #4 @ then skip it, returning non-zero r12 value @ put some instruction here which is architecturally defined as @ invalid, or is there something fast model specific we can use @ to get better diagnostics? > There are open issues with the code, somebody can clarify: > 1. Is the default secure vector table being used in other palce? I > didn't find. But if yes, I should restore secure vector table. > 2. When return from data abort exception, I added two 'nop' instruction. > Without them, the instruction 'cmp r4, #0xba' seems not function > correctly. That's really tricky. > - I tried to use exception return instruction 'subs pc, lr, #8'. It doesn't help. "subs pc, lr, #8" would return to the instruction which faulted which would go a bit wrong as it would use the new r4 value to read from memory again. "subs pc, lr, #4" is what you need to return to the instruction after the faulting ldr instruction. -- Tixy _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
