[LLVMdev] Code generation support in llvm for windows phone

Saleem Abdulrasool
Sat, 07 Jun 2014 21:23:29 -0000

On Sat, Jun 7, 2014 at 10:06 AM, C K Kashyap <ckkashyap at gmail.com>
wrote:

> Hi Saleem,
> I have a similar situation - I'd appreciate your inputs on it. I
noticed
> that the obj file generated using llvm does not contain "thumb"
> instructions. I suspect that is what is causing runtime crash for me.
>
>
> Here's what I've tried -
> Start with a.c (on my linux machine where I have llvm/clang built as of
> yesterday)
>                       int add(int i, int j) {int k = i + j; return k; }
> clang  -S  -O0  a.c
>

This targets the default target, which may not necessarily be the target
that you want.


> llc -filetype=obj -mtriple=thumbv7-windows -O0 a.ll
>

This is a bit round-about to generate the object-file.

You can actually generate the object file directly from clang at this
point, which may not have been the case when you first started looking at
this.

$ clang -target armv7-windows -c a.c -o a.obj

If you look at the generated assembly, you will find that it will generate
a thumb function, even though the object file may be missing the
appropriate flag in the case of the public llvm repository (Ill look into
that btw).

I get a.obj from the above steps.
>
> I take this a.obj over to my windows 8.1 machine where I have VS2013
> update 2 installed
>
> I open up a command window and run
> C:\Users\kck\arm>"c:\Program Files (x86)\Microsoft Visual Studio
> 12.0\vc\bin\x86_arm\vcvarsx86_arm.bat"
>
> I create a file file m.c
> int main() { return add(20,30);}
>

This might cause an issue.  You are not providing a declaration for the
symbol.  If cl ends up converting it to a dllimport'ed symbol, the
generated application will not execute.


> I build the whole thing like this -
>
> cl m.c a.obj
>

That seems right; I will note that all my testing with cl has been with /MD.


> Things seem  to work fine and m.exe gets generated.
>
> However I noticed a difference in the dumpbin output for a.obj and m.obj -
> In m.obj, I can see "Thumb instructions" where as in a.obj, I
don't see
> that.
>

I'll look into that, but, I suspect that this is not the cause of the crash.


> I'd appreciate any pointers on this.
>

Can you specify what the target environment is?  (Device, Windows version,
etc).

Actual details of the crash may also be relevant.  Also of interest would
be how you are loading the generated binary onto the device.  The only way
that I know of accomplishing that involves the use of Visual Studio's
remote debugging functionality.


> Regards,
> Kashyap
>
>
>
>
>
>
> On Fri, May 30, 2014 at 10:45 PM, Saleem Abdulrasool <abdulras at
fb.com>
> wrote:
>
>>
>> On May 28, 2014, at 5:18 AM, Rajat Mahajan <rmahajan at
adobe.com> wrote:
>>
>> > I am talking about Windows Mobile 8 and 8.1 and not CE.
>> > Not sure though that the Windows 8 (ARM NT) is similar to Windows
>> Mobile 8 platform.
>> >
>> > I used the following command to generate the obj file
>> >    Llc.exe -mtriple=thumbv7-windows  -filetype=obj
<some_name>.bc
>> >
>> > The object file generated in the above object doesn't get
linked when I
>> try to link it with the windows mobile library as it fails to recognize
the
>> object format.  ( Not a valid object file )
>> >
>> > Hope I am clear.
>>
>> Unfortunately, you have merely repeated your previous statement.  I
don’t
>> have enough here to diagnose nor even speculate what is going on.
>>
>> If you can provide the object file, it would be helpful as I am unable
to
>> reproduce this issue.  Although, I ran it via clang, I see no reason
that
>> the output would be different as the backend is the same.
>>
>> The triple is certainly correct (particularly for llc, clang will treat
>> armv7-windows as thumbv7-windows).  How did you generate the bit code?
My
>> testing has usually started from C or LLVM IR rather than bit code,
but, I
>> suspect that shouldn’t be a real issue.
>>
>> With the given information, the only thing that comes to mind is that
>> your environment is setup improperly, resulting in the wrong link.exe
being
>> invoked.
>>
>> > ~rajat
>> >
>> > -----Original Message-----
>> > From: Saleem Abdulrasool [mailto:abdulras at fb.com]
>> > Sent: Friday, May 16, 2014 11:23 PM
>> > To: Rajat Mahajan
>> > Cc: llvmdev at cs.uiuc.edu
>> > Subject: Re: [LLVMdev] Code generation support in llvm for windows
phone
>> >
>> >
>> > On May 16, 2014, at 6:53 AM, Rajat Mahajan <rmahajan at
adobe.com> wrote:
>> >
>> >> Hi,
>> >>
>> >> Is there support available in llc to convert llvm bytecode to
Windows
>> Mobile binary?
>> >> I have tried triples like arm-pc-win32 , thumbv7-window ...
but the
>> object file generated is not getting linked to the windows native
project.
>> >> Any pointers will be greatly appreciated?
>> >
>> > As Reid mentioned, I have been working on this recently.  Just to
make
>> sure that we are talking about the same environment, I assume that you
are
>> talking about Windows 8 (ARM NT) rather than the Windows CE based
>> environment.
>> >
>> > Can you please explain what exactly you mean by "the object
file
>> generated is not getting linked to the windows native project".
The object
>> file that we generate should be pretty compatible with MSVC.  If you
have
>> specific cases where we are generating something that is incompatible,
I
>> would be quite interested in hearing about that.
>> >
>> >> Thanks,
>> >> ~rajat
>> >> _______________________________________________
>> >> LLVM Developers mailing list
>> >> LLVMdev at cs.uiuc.edu
>>
https://urldefense.proofpoint.com/v1/url?u=http://llvm.cs.uiuc.edu/&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=CchYc4lrV44%2BZqxZADw0BQ%3D%3D%0A&m=4sS%2FRJsOxjeRZpxwDsr85CHzLMrTV5IeD%2Bf2OnxlCFY%3D%0A&s=64253b311de373a46904eada51eb8c9f732f8f65d14f0551223b2a7c769f135a
>> >>
>>
https://urldefense.proofpoint.com/v1/url?u=http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=CchYc4lrV44%2BZqxZADw0BQ%3D%3D%0A&m=4sS%2FRJsOxjeRZpxwDsr85CHzLMrTV5IeD%2Bf2OnxlCFY%3D%0A&s=5c75919fb4cc3458c6e733d0d672d937dca015122c56ab7b826bc6b5ae74a594
>> >
>> > --
>> > Saleem Abdulrasool
>> > abdulras (at) fb (dot) com
>> >
>> >
>> >
>> >
>> >
>>
>> --
>> Saleem Abdulrasool
>> abdulras (at) fb (dot) com
>>
>>
>>
>>
>>
>>
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--
Saleem Abdulrasool
compnerd (at) compnerd (dot) org
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