> On May 18, 2016, at 6:01 PM, Saleem Abdulrasool <compn...@compnerd.org> wrote:
>
> On Wednesday, May 18, 2016, Joe Groff <jgr...@apple.com> wrote:
>
> > On May 18, 2016, at 1:51 PM, Saleem Abdulrasool via swift-dev
> > <swift-dev@swift.org> wrote:
> >
> > Hi,
> >
> > It seems that there are assumptions about the ability to create relative
> > address across sections which doesn't seem possible on Windows ARM.
> >
> > Consider the following swift code:
> >
> > final class _ContiguousArrayStorage<Element> { }
> >
> > When compiled for Windows x86 (via swiftc -c -target i686-windows
> > -parse-as-library -parse-stdlib -module-name Swift -o Swift.obj
> > reduced.swift) it will generate the metadata pattern as:
> >
> > __TMPCs23_ContiguousArrayStorage:
> > ...
> > .long
> > __TMnCs23_ContiguousArrayStorage-(__MPCs23_ContiguousArrayStorage+128)
> > ...
> >
> > This generates a IMAGE_REL_I386_REL32 relocation which is the 32-bit
> > relative displacement of the target.
> >
> > On Windows ARM (swiftc -c -target i686-windows -parse-pas-library
> > -parse-stdlib -module-name Swift -o Swift.obj reduced.swift) it will
> > generate similar assembly:
> >
> > _TMPCs23_ContiguousArrayStorage:
> > ...
> > .long
> > _TMnCs23_ContiguousArrayStorage-(_MPCs23_ContiguousArrayStorage+128)
> > ...
> >
> > However, this generates an IMAGE_REL_ARM_ADDR32 relocation which is the
> > 32-bit VA of the target. If the symbol are in the same section, it is
> > possible to get a relative value. However, I don't really see a way to
> > generate a relative offset across sections. There is no relocation in the
> > COFF ARM specification which provides the 32-bit relative displacement of
> > the target. There are 20, 23, and 24 bit relative displacements designed
> > specifically for branch instructions, but none that would operate on
> > generic data.
> >
> > Is there a good way to address this ABI issue? Or perhaps do we need
> > something more invasive to support such targets? Now, I might be
> > completely overlooking something simple that I didn't consider, so pointing
> > that out would be greatly appreciated as well.
>
> That's unfortunate. One possibly-crazy solution would be to use a different
> object format that does support the necessary relocations, such as LLVM's
> win32-macho target. That would forgo interoperability with non-LLVM
> toolchains, of course
>
> Yeah, it would make interoperability harder. But, is there a loader for
> macho on Windows?
Sorry, if it wasn't clear, I meant that you could use mach-o (or ELF, or any
object format really) for .o and .a files. You'd still link them into PE
executables and DLLs.
-Joe
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