[LLVMdev] Support for Windows Phone 8.1

Damanjit Singh dsingh at adobe.com
Wed Jun 18 09:09:59 PDT 2014 

Hi Saleem,

Though a simple app works great I am facing few issues trying to link a slightly complex object file, generated via LLVM, with some libs generated via Visual Studio -
1. Seems IMAGE_SCN_MEM_16BIT is only written for the the first header in the COFF file, thus functions in other headers (if you are using function sections) don’t work. I was able to workaround this by forcing this entry for each header by making some (hacky) changes in LLVM sources. I am not much familiar with the LLVM source code, thus would better let the experts to do a correct fix for this issue.
2. There is something strange happening with b.w instruction in the final linked executable. I see that in the disassembly for object code (generated via LLVM with thumbv7-windows-msvc triple), the b.w instruction correctly points to the label I want. But after linking, it now points to some random address. Seems like there are some fixup issues related to b.w instruction. Note that I am using Visual Studio’s linker to create a Window’s phone app.

I would really appreciate any help, or pointers for further investigation, for the second issue above.

Thanks,
Daman

On 09/06/14 8:45 pm, "Saleem Abdulrasool" <abdulras at fb.com<mailto:abdulras at fb.com>> wrote:


On Jun 8, 2014, at 10:46 PM, Damanjit Singh <dsingh at adobe.com<mailto:dsingh at adobe.com>> wrote:

Thanks a lot Saleem,
The issue is fixed and a simple app works fine now.

Awesome; thanks for the verification.

-Daman
On 08/06/14 12:57 pm, "Nick Lewycky" <nicholas at mxc.ca<mailto:nicholas at mxc.ca>> wrote:
Damanjit Singh wrote:
Thanks Saleem, Nick.
I will try with the latest code and share the results.
Though, just curious if I need to really use clang to generate the
object file and the current steps won't work? I ask because using .c
file was only an illustration. For my project the IR is not generated
from .c files or clang.
You don't need to use clang. When you use clang you have to tell it what
target it's targeting.
If you're starting with IR, try "llc -filetype=obj foo.bc -o foo.obj
-mtriple=..." to produce a .o file directly. I'm not experienced with it
myself but I've heard that MSVC will produce assembly that it can't
parse, so it's probably a good idea to leave assembly out of the
equation when targeting Windows.
Nick
On 08-Jun-2014, at 11:00 am, "Saleem Abdulrasool" <compnerd at compnerd.org<mailto:compnerd at compnerd.org>
<mailto:compnerd at compnerd.org>> wrote:
On Sat, Jun 7, 2014 at 4:49 PM, Nick Lewycky <nicholas at mxc.ca<mailto:nicholas at mxc.ca>
<mailto:nicholas at mxc.ca>> wrote:
    Damanjit Singh wrote:
        Hi guys,
        Would really appreciate any help here.
        Thanks,
        Daman
        From: Damanjit Singh <dsingh at adobe.com<mailto:dsingh at adobe.com>
        <mailto:dsingh at adobe.com> <mailto:dsingh at adobe.com>>>         <mailto:dsingh at adobe.com>>>
        Date: Friday, 6 June 2014 12:57 pm
        To: "llvmdev at cs.uiuc.edu<mailto:llvmdev at cs.uiuc.edu> <mailto:llvmdev at cs.uiuc.edu>
        <mailto:llvmdev at cs.uiuc.edu%20%3Cmailto:llvmdev at cs.uiuc.edu>>"
        <llvmdev at cs.uiuc.edu<mailto:llvmdev at cs.uiuc.edu> <mailto:llvmdev at cs.uiuc.edu>
        <mailto:llvmdev at cs.uiuc.edu%20%3Cmailto:llvmdev at cs.uiuc.edu>>>
        Subject: Support for Windows Phone 8.1
        Hi LLVMdev,
        Does the latest trunk code support Windows Phone 8.1 target ?
    I don't know this, but ...
        I was trying out a simple program, but Visual Studio 2013¹s
linker
        failed for me with this error - app.obj : error LNK2008: Fixup
        target is
        not aligned Œadd3'
        This is what I tried -
        * Download latest LLVM sources (as on 4th June) and build them
        on my
        MAC 10.9 machine.
        * Wrote a simple a.c, with add3 function-
        int add3(int i, int j)
        {
        int k = i+j;
        return k;
        }
        * Create LLVM IR using Xcode 5.1¹s clang ( *clang ­S -O0
        -emit­llvm a.c* )
        * Create obj file ­ using llc - *. /i686-apple-darwin11-llc
        -filetype=obj -mtriple=thumbv7-windows-msvc -O0 a.s *
    ... in general this doesn't work. The transformation from C to
    LLVM IR needs to know the target triple. Try "clang
    --target=thumbv7-windows-msvc a.c -c -o a.obj"? Since clang has a
    built-in assembler, you should get a valid COFF file out, to the
    extent that clang and llvm support this target.
    If that doesn't work, I may suggest it's unsupported.
As Nick mentioned, please generate the object file directly from
clang. You can use armv7-windows or thumbv7-windows (clang will
translate armv7-windows to thumbv7-windows implicitly). I just fixed a
bug that should allow you to link the object files with link.
    Nick
        * Now on a Windows 8.1 Desktop machine, link this object file
        into
        sample (new DirectX app, windows phone) Visual Studio 2013
        project.
        * Declare and Call add3 in the sample windows project.
        * I then get a linker error on building the solution.
        *1>app.obj : error LNK2008: Fixup target is not aligned 'add3'*
        *1>LINK : fatal error LNK1165: link failed because of fixup
        errors*
        *========== Rebuild All: 0 succeeded, 1 failed, 0 skipped
        ==========*
        Could someone please confirm about the state of support for
        Windows
        Phone 8.1 ? Or am I missing something here?
        Thanks,
        Daman
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--
Saleem Abdulrasool
compnerd (at) compnerd (dot) org
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