[cfe-dev] Building for target armv7a-win32-eabi not possible

Peter Smith via cfe-dev cfe-dev at lists.llvm.org
Tue Oct 2 03:57:29 PDT 2018


On Tue, 2 Oct 2018 at 11:39, Jayvee Neumann <jayvee.neumann at gmail.com> wrote:
>
> Hello Peter,
>
> thank you for the quick answer.
> Actually I do want ARM code and not Thumb code. The dynamic library I try to build will be used from an environment that expects to call ARM code. I have no influence on the fact that I need ARM code. I am also supposed to link statically to a specialized prebuilt library providing runtime symbols such as "__rt_sdiv" (platform "none" will need symbols such as "__divsi3" for comparison). I have no influence on this circumstance, either.
>
> This means the target armv7a-none-eabi is useless to me, as neither the object format nor the expected runtime functions match my requirements.
>
> So the original problem remains.
>

I think that you may be out of luck using clang as the Windows on ARM
support is currently only Windows ARM NT which only supports Thumb,
hence the clang/llvm implementation only supports Thumb. My source is
https://reviews.llvm.org/D43005#1000822 . I'm guessing you are
targetting some kind of older Windows CE device that supported Arm
instructions?

Apologies I can't be of more help. Maybe some people in the US
timezone will know more.

Peter

> Best regards,
> Jayvee
>
> Am Di., 2. Okt. 2018 um 12:04 Uhr schrieb Peter Smith <peter.smith at linaro.org>:
>>
>> Hello Jayvee,
>>
>> On Tue, 2 Oct 2018 at 10:30, Jayvee Neumann via cfe-dev
>> <cfe-dev at lists.llvm.org> wrote:
>> >
>> > Hello together,
>> >
>> > I have a question regarding the the target triple armv7a-win32-eabi. I want to emit ARM code (not thumb code) for windows. The object file should be in COFF.
>> > When calling clang++ with that target and the "--verbose" switch, I can see that the generated triple is "tumbv7--windows-eabi". This is explicitly not what I specified as a target.
>> > I then went ahead and changed the generated call to use "-triple armv7a--windows-eabi". This resulted in the compiler error:
>> > > error: Function 'func' uses ARM instructions, but the target does not support ARM mode execution.
>> > > fatal error: error in backend: unsupported relocation type: fixup_arm_uncondbl
>> >
>> > The question I have is, why is it prohibited to export ARM code for win32? When I replace "win32" with "none" I get no such error.
>> >
>>
>> My, somewhat limited, understanding is that Windows for Arm is
>> designed only for Thumb, for example there may be places in the tools
>> and the OS that don't handle interworking between Arm and Thumb
>> correctly. This prevents Arm instructions from being used safely on
>> the platform. When you remove the win32 with none you are removing
>> that platform specific restriction, however you are probably not
>> getting a Windows compatible COFF file out either.
>>
>> I think you'll also not want EABI in your triple as that is the ELF
>> ABI and not the Windows compatible COFF ABI that you'll need on
>> Windows. You may want to try a target like thumbv7a-windows-msvc
>>
>> Peter
>>
>> > Best regards,
>> > Jayvee
>> > _______________________________________________
>> > cfe-dev mailing list
>> > cfe-dev at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev


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