[llvm-commits] [llvm] r123424 - in /llvm/trunk: include/llvm/Object/MachOFormat.h lib/MC/ELFObjectWriter.cpp lib/MC/MachObjectWriter.cpp lib/Target/ARM/ARMAsmBackend.cpp lib/Target/ARM/ARMFixupKinds.h lib/Target/ARM/ARMMCCodeEmitter.cpp test/MC/A

[Evan Cheng]

On Jan 18, 2011, at 12:22 PM, Jason Kim wrote:

> On Fri, Jan 14, 2011 at 3:38 PM, Evan Cheng <evan.cheng at apple.com> wrote:
>> 
>> On Jan 14, 2011, at 12:20 PM, Jason Kim wrote:
>> 
>> 
>> Hi Evan,
>> 
>> FYI, the movt hi16 fixup you put in does not match the output of GNU as -
>> Let me look into this and figure out why. I'll reply soon.
>> 
>> -jason
>> 
>> 
>> Interesting. That's probably due to this:
>> 
>>   case ARM::fixup_arm_movt_hi16:
>> 
>> -  case ARM::fixup_arm_movw_lo16:
>> 
>>   case ARM::fixup_arm_movt_hi16_pcrel:
>> 
>> +    Value >>= 16;
>> 
>> +    // Fallthrough
>> 
>> +  case ARM::fixup_arm_movw_lo16:
>> 
>>   case ARM::fixup_arm_movw_lo16_pcrel: {
>> 
>>     unsigned Hi4 = (Value & 0xF000) >> 12;
>> 
>>     unsigned Lo12 = Value & 0x0FFF;
>> 
>> @@ -168,6 +175,26 @@
>> 
>>     Value = (Hi4 << 16) | (Lo12);
>> 
>>     return Value;
>> 
>>   }
>> 
>> Notice the Value is shifted down 16 bits for movt. I'm fairly sure this is
>> right, at least for Darwin. It's possible there is a bug elsewhere.
>> Evan
>> 
>> 
> 
> Hmm, I see at least one problem that was not caught earlier -
> 
> 1) movw/movt paired with :lower16:/:upper16:
> 2) movw/movt NOT paired with a :lower16:/:upper16:
> 
> The handling has to be different for these two cases
> in case 2, the constant will already be a 16bit value
> in case 1, the constant will need to be right shifted (during? before? fixup)
> 
> It seems like this needs to be handled before the fixup actually happens.
> 
> Does Darwin assembler require :lower16:/:upper16: when using movw/movt?

I believe so. Kevin?

Evan

> 
> -jason