[swift-dev] SwiftGlibc: Use VFS overlay instead of -fmodule-map-file

[Jordan Rose]

Hi, Rintaro. That’s a clever solution; it would mean we wouldn’t be blocked by talking to the Clang folks about making module map search paths SDKROOT-relative. That said, the VFS is a fairly, well, hacky piece of Clang, and I’m not sure we’d want to add a new dependency on it. Ben, Daniel, what do you think?

Jordan

> On May 21, 2016, at 05:36, rintaro ishizaki via swift-dev <swift-dev at swift.org> wrote:
> 
> Hi all,
> 
> Recently, a couple of PR are posted regarding
> glibc.modulemap in cross-compiling environment.
> 
> https://github.com/apple/swift/pull/2473 <https://github.com/apple/swift/pull/2473>
> https://github.com/apple/swift/pull/2486 <https://github.com/apple/swift/pull/2486>
> 
> The problem is that glibc.modulemap contains hardcoded SDKROOT in it.
> To resolve that, how about using virtual file system feature in Clang?
> 
> I mean, prepare YAML like this:
> 
> {
>   "use-external-names": false,
>   "roots": [
>     {
>       "type": "file",
>       "name": "${SYSROOT}/usr/include/module.map",
>       "external-contents": "${RSRC}/${platform}/${arch}/glibc.modulemap"
>     }
>   ]
> }
> 
> Then, invoke Clang with -ivfsoverlay argument.
> 
> Of course, we have to dynamically create YAML based on -sdk and -target
> argument of the Swift compiler.
> Luckily, Clang provides convenient YAML builder for this:
> http://clang.llvm.org/doxygen/classclang_1_1vfs_1_1YAMLVFSWriter.html <http://clang.llvm.org/doxygen/classclang_1_1vfs_1_1YAMLVFSWriter.html>
> It's easy and trivial work to build that dynamically.
> 
> Using this feature, glibc.modulemap can be rather simple.
> No need to specify absolute path.
> It can be simple as /usr/include/module.map in Darwin platforms:
> 
>     module ctype {
>       header "ctype.h"
>       export *
>     }
> 
> And, it makes easy to import Clang builtin headers like "limits.h".
> 
> Here is the PoC code:
> https://github.com/apple/swift/compare/master...rintaro:clang-vfsoverlay <https://github.com/apple/swift/compare/master...rintaro:clang-vfsoverlay>
> It works, and passes all Swift test suite.
> 
> Current my concerns are:
> * The VFS overlay is the right way in the first place?
> * Since I'm a very newbie in C++ programming, I'm not sure I'm doing right thing in the code.
> 
> Any thought?
> 
> _______________________________________________
> swift-dev mailing list
> swift-dev at swift.org
> https://lists.swift.org/mailman/listinfo/swift-dev

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-dev/attachments/20160523/ae457d9e/attachment.html>