[LLVMdev] switching ARM modes and integrated-as

[Greg Fitzgerald]

Done, thanks.  And added a code review here:

http://llvm-reviews.chandlerc.com/D2255

-Greg

On Fri, Nov 22, 2013 at 8:48 AM, Amara Emerson <amara.emerson at arm.com> wrote:
> Hi Greg,
>
> Can you post any patches to the commits list, it'll have a better chance of
> some of us seeing it and taking a look there.
>
> Cheers,
> Amara
>
> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On
> Behalf Of Greg Fitzgerald
> Sent: 22 November 2013 00:56
> To: 'Jim Grosbach'; 'Evan Cheng'
> Cc: llvmdev at cs.uiuc.edu
> Subject: Re: [LLVMdev] switching ARM modes and integrated-as
>
> Looks like the bug here is that the InlineAsm parser and the ARM code
> emitter point to two different TargetSubtargetInfo instances.  The attached
> patch corrects the issue, but is incomplete.  For starters, how can I remove
> that const_cast?  Also, the patch does not restore the TargetSubtargetInfo
> to its original state.  So if you changed from Thumb to ARM mode, but not
> back to Thumb, the code emitter will generate broken machine code.
> Unfortunately, the TargetSubtargetInfo class does not expose a copy
> constructor or a setFeatureBits() method.  Should it?  Or should we expect
> the inline assembly to be responsible for restoring the mode itself?
>
> Thanks,
> Greg
>
> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On
> Behalf Of Greg Fitzgerald
> Sent: Tuesday, November 19, 2013 11:07 AM
> To: Jim Grosbach
> Cc: llvmdev at cs.uiuc.edu List
> Subject: Re: [LLVMdev] switching ARM modes and integrated-as
>
>> I just tried the above code in a .s file and it worked fine for me.
>> Can you show exactly what you're seeing that looks wrong?
>
> Thanks Jim.  I can only reproduce the issue when that code is inline
> assembly in a bitcode file.  Attached is a bitcode file and Makefile to
> demonstrate.  Calling 'make' will dump two object files 'c.o' and 'asm.o'.
> The former is created with llc directly, whereas the latter first generates
> an assembly file and then assembles it via llvm-mc.
> The issue is only present when directly generating the object file.
> You can see that the first ARM instruction, push {r7}, is encoded as
> 7004e52d and not e52d7004.
>
> Thanks,
> Greg
>
> On Mon, Nov 18, 2013 at 6:33 PM, Jim Grosbach <grosbach at apple.com> wrote:
>>
>> On Nov 18, 2013, at 6:18 PM, Greg Fitzgerald <garious at gmail.com> wrote:
>>
>>> Does the integrated assembler in the ARM backend support switching
>>> between ARM and Thumb modes in the same file?
>>
>> Yes.
>>
>>>  I'm having trouble with
>>> the following assembly:
>>>
>>>  .thumb_func
>>>  @   Enter ARM mode
>>>  adr r3, 1f
>>>  bx  r3
>>>  .align 4
>>
>> That .align is probably not what you want. ARM .align is a power of two,
> so you're aligning at 16 bytes here, not 32-bits.
>>
>>>  .code 32
>>> 1:  push {r7}
>>>  mov r7, r12
>>>  svc 0x0
>>>  pop {r7}
>>>  @   Enter thumb mode
>>>  adr r3, 2f+1
>>>  bx  r3
>>>  .code 16
>>> 2:
>>>  bx  lr
>>>
>>>
>>> As a standalone .s file, GNU-as can compile it but with "clang
>>> -integrated-as", I get errors.  If using inline assembly in a C file,
>>> no error is reported (when compiled targeting thumb 2), but the
>>> 32-bit ARM instructions are encoded wrongly.  The two 16-bit halves
>>> need to be swapped.  A bug, unsupported, or perhaps just user error?
>>
>> I just tried the above code in a .s file and it worked fine for me. Can
> you show exactly what you're seeing that looks wrong? Note that Thumb2 wide
> instructions have the two half-words swapped from what one would expect.
> Possibly the disassembly isn't identifying arm vs. thumb code and that's
> what's making things look wrong?
>>
>>>
>>> Thanks,
>>> Greg
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>
>
>
>
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