On 3/11/20 1:58 PM, Eugeniy Paltsev wrote: >> >> I would like to keep it aligned. >> >> ARC700 definitely has penalty for unaligned branch targets, so it will definitely >> suffer there. > > Do you know some exact numbers? I'm not an expert in ARC700 (fortunately =) I don't remember the exact numbers either. >> For HS, unaligned branch targets have no penalty (for the general case atleast), >> but if it does get unaligned, the entire entry prologue code will be - i.e. each >> one of the subsequent 130 or so instructions. That doesn't seem like a good idea >> in general to me. > > I really don't insist about applying this patch but I don't understand your > argumentation about ARC HS like at all. I knew you would argue hence I already copy/pasted the start and end of the epilogue already in my prev reply which you didn't care to read thru. If you start counting instructions from <ret_from_exception> all the way to end of <debug_marker_ds> there are over 130 instructions all of which can be rendered unaligned by your patch. What is worse is that this would be unpredictable: the unaligned case will mostly NOT happen, but a new compiler or some subtle code change could causing potentially side-effects we won't even know where to look. >> I faked it using a nop_s and the SYM_FUNC_START_NOALIGN( ) annotation and can see >> all instructions getting unaligned. > > What is the problem with it? It's totally valid and fine for ARC HS to have instructions > aligned by 2 byte. Or are you talking about ARC700 again? Yes I know that already. It is fine in general as I explained earlier, but can potentially NOT when 130 instructions are unaligned. >> Before; >> >> 921238e4 <ret_from_exception>: >> 921238e4: ld r8,[sp,124] >> 921238e8: bbit0.nt r8,0x7,212 >> ... >> 92123ac8: rtie >> 92123acc <debug_marker_ds>: >> 92123acc: ld r2,[0x927d81d8] >> 92123ad4: add r2,r2,0x1 >> 92123ad8: st r2,[0x927d81d8] >> 92123ae0: bmskn r11,r10,0xf >> 92123ae4: sr r11,[aux_irq_act] >> 92123ae8: b -140 ;92123a5c >> >> After: >> >> 9212393c: nop_s >> 9212393e <ret_from_exception>: >> 9212393e: ld r8,[sp,124] >> 92123942: bbit0.nt r8,0x7,214 >> ... >> 92123b22: rtie >> 92123b26 <debug_marker_ds>: >> 92123b26: ld r2,[0x927d81d8] >> 92123b2e: add r2,r2,0x1 >> 92123b32: st r2,[0x927d81d8] >> 92123b3a: bmskn r11,r10,0xf >> 92123b3e: sr r11,[aux_irq_act] >> 92123b42: b -138 ;92123ab6 <debug_marker_syscall> >> 92123b46: nop_s _______________________________________________ linux-snps-arc mailing list linux-snps-arc@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/linux-snps-arc
