Code generation support in llvm for windows phone

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?

Thanks,

~rajat

No - to my knowledge no one has suggested or attempted any such project/support.

- David

I think Saleem has been working on this. It’s in a pretty early stage, so far as I know.

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.

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.
~rajat

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.

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

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);}

I build the whole thing like this -

cl m.c a.obj

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’d appreciate any pointers on this.

Regards,
Kashyap

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.

Thank you so much Saleem,
The target is Windows phone 8.1 (ARM). I’ll update the crash details tomorrow. One big problem is that I have to use a physical windows phone for execution.
I wonder if it is possible to execute such “exes” using qemu.
Regards,
Kashyap

Thank you so much Saleem,
The target is Windows phone 8.1 (ARM). I'll update the crash details
tomorrow.

Please rebuild the tree after SVN r210415 when you test it again. It seems
that link.exe needs the IMAGE_SCN_MEM_16BIT set in order to select the
function as a thumb function rather than silently assuming that all
functions are thumb (which was something that I suspected but hadn't tested
since I haven't been using that linker for my testing).

If you were seeing an "Invalid Instruction" exception, that was caused by
the application switching into ARM mode execution (rather than staying in
thumb mode as it should).

Please let met know what the result is with your test, as I do want to
ensure that this does play well with the Visual Studio toolchain.

One big problem is that I have to use a physical windows phone for

execution.

I wonder if it is possible to execute such "exes" using qemu.

Please let me know if you get that to work somehow (I don't know if there
is a way to do that currently).

Wow … I did a git pull on llvm and clang compiled my c file
clang -target thumbv7-windows -c -O0 a.c -oa.obj

dumpbin /all on a.obj now shows “thumb instructions” … I’ll try running this tomorrow and post back.

Regards,
Kashyap

yeah … the app runs perfectly. Thank you so much Saleem.
Regards,
Kashyap